coverity null pointer dereference

accesses memory stored at its address. If it wasn't for coverity Resource leaks: I hate them, especially in libc, which is code you expect to be hot. Our code base contains a lot of copy paste mistakes, we are glad that there is a tool like coverity that can help to detect them. This fault is buried deep within some complex logic that makes it really hard to track. This one alone We had some spurious hangs and never knew why. How a top-ranked engineering school reimagined CS curriculum (Ep. This solution also ensures that theuser_data pointer is not null. (where the weakness is a quality issue that might indirectly make it easier to introduce security-relevant weaknesses or make them more difficult to detect). Right? By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. Even documented "we don't need to care, I think" issue can become an issue when one does not check the background implementation. Buffer overflow difficult to find by reading the code that would result a crash if path is too long. It was causing glusterd daemon crash for glusterfs. The indicated severity is for this more severe case; on platforms where it is not possible to exploit a null pointer dereference to execute arbitrary code, the actual severity is low. Checker. Dereferencing a null pointer is undefined behavior, typically abnormal program termination. Why did DOS-based Windows require HIMEM.SYS to boot? No affinity group collision detected for cluster {}. A Pillar is different from a Category as a Pillar is still technically a type of weakness that describes a mistake, while a Category represents a common characteristic used to group related things. REVERSE_INULL False Positive "Dereference before NULL check" See C17 7.1.4p1, which says, in part: Each of the following statements applies unless explicitly stated otherwise in the detailed descriptions that follow: If an argument to a function has an invalid value (such as a value outside the domain of the function, or a pointer outside the address space of the program, or a null pointer, or a pointerto non-modifiable storage when the corresponding parameter is not const-qualified) or a type (after default argument promotion) not expected by a function with a variable number of arguments, the behavior is undefined. This weakness can be detected using dynamic tools and techniques that interact with the software using large test suites with many diverse inputs, such as fuzz testing (fuzzing), robustness testing, and fault injection. rev2023.5.1.43405. Typically, this is done by building a model of data flow and control flow, then searching for potentially-vulnerable patterns that connect "sources" (origins of input) with "sinks" (destinations where the data interacts with external components, a lower layer such as the OS, etc. Phew, we're agreed here. These types of problems usually lead to insidious correctness errors since exceptions are caught at a higher level. And the compliant solution guarantees that the pointer will be valid if the code calls memcpy(). One of the Coccinelle software maintainers expressed opposite development views today. Although i'm only We haven't noticed an impact of the bug but the out of bounds access has been present since at least 2009 without anybody spotting it. If code1 and code2 may both be true, though, then you do have a substantial bug here. For users who are concerned with the practical application and details about the nature of a weakness and how to prevent it from happening. <<< CID 102061: Null pointer dereferences REVERSE_INULL <<< Null-checking " doc_bv " suggests that it may be null, but it has already been dereferenced on all paths leading to the check. Why does the narrative change back and forth between "Isabella" and "Mrs. John Knightley" to refer to Emma's sister? Good question! I suggest that this topic needs to include calloc() and realloc() Refer to Linux man pages online for more enlightenment about malloc(), and friends. So the SIZE_MAX check was unnecessary. Common logic to perform in the middle? Synopsys, Inc. | Policy Statement | Contact, // Create a set of all VMs in affinity groups, // There is no need to migrate when no collision was detected. Either the check against null is unnecessary, or there may be a null pointer dereference. Note that 7.1.4 explicitly states that a null pointer is not a valid pointer argument. with solve of this bug problems have gone. I have simplified it below (with the first warning)-, The code goes on to do several operations with a_ptr. c++ - Coverity -- Explicit null dereference - Stack Overflow This defect on our template caused null pointer deferencing in over hundred use cases. Network monitor allows remote attackers to cause a denial of service (crash) via a malformed Q.931, which triggers a null dereference. 0->member is undefined behavior. COVERITY checker description | The STAR experiment Right? The code is dead and will be never processed because 'decoded' outside the scope and redefined in local. assert(!invalid(p)); // or whatever, bool invalid(const void *p) { String URL = intent.getStringExtra("URLToOpen"); func HandleRequest(client http.Client, request *http.Request) (*http.Response, error) {. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. This compliant solution ensures that the pointer returned by png_malloc() is not null. It could cause e-mails stored with incorrect names. You have defined pointers var1 and var2 of type uint64_t and char respectively which are pointing to NULL . Aaron:I suspect we are talking past each other. Identify error conditions that are not likely to occur during normal usage and trigger them. If you don't set it again before the above if statement, that means that the NULL check is unnecessary and should be removed. FORWARD_NULL: A program will normally crash when a NULL pointer is dereferenced. The expression x.Equals(null) will throw NullReferenceException if x is null. This code also violates ERR33-C. Detect and handle standard library errors. The libpng library implements its own wrapper to malloc() that returns a null pointer on error or on being passed a 0-byte-length argument. Coverity Prevent cannot discover all violations of this rule, so further verification is necessary, Detects when NULL is dereferenced (Array of pointers is not checked. NIST. This warning thrown by Coverity if you dereference a pointer and then later on do a NULL check on it. The user_data pointer could be invalid in other ways, such as pointing to freed memory. ), Does not guess that return values from malloc(), strchr(), etc., can be NULL (The return value from malloc() is NULL only if there is OOMo and the dev might not care to handle that. The software's operation may slow down, but it should not become unstable, crash, or generate incorrect results. }. This is not a perfect solution, since 100% accuracy and coverage are not feasible. In this noncompliant code example, input_str is copied into dynamically allocated memory referenced by c_str. http://blog.llvm.org/2011/05/what-every-c-programmer-should-know_14.html. The 2nd NCCE/CS pair seems redundant with the first NCCE/CS pair. But passing 0 to memcpy() is not one of them. See the "Null pointer checks may be optimized away more aggressively" section inhttps://gcc.gnu.org/gcc-4.9/porting_to.htmlas an example with one common implementation. 2012-09-11. Thanks for contributing an answer to Stack Overflow! So no checking of the length is necessary (besides preventing integer overflow, which the compliant solution does). When length is zero, it is probably unusable condition for this function. A deferred call's arguments are evaluated immediately, so the defer statement panics due to a nil response. What is the symbol (which looks similar to an equals sign) called? */. Wikipedia. C/C++ Dereference error: Dereference before null check, Solving C warning - dereferencing a null pointer. For example, there may be high likelihood that a weakness will be exploited to achieve a certain impact, but a low likelihood that it will be exploited to achieve a different impact. 2005-11-07. However, the warning has value because it is pointing [sic] out that the safety of q is not trivially obvious from your function's logic. This code also violates ERR33-C. Detect and handle standard library errors. int changed to size_t and if size_t parameter's is zero, allocate one word. 412-268-5800, If an argument to a function has an invalid value (such as a value outside the domain of the function, or a pointer outside the address space of the program, or a null pointer, or a pointer. Specifically, it understands that Equals is meant to test equality, and that you're comparing x to null as if they might be the same (the "check"), but you can't get into Equals (the "path") at all because of the NullReferenceException. Description. Is "I didn't think it was serious" usually a good defence against "duty to rescue"? This fixed weird behaviour that was really hard to find. uint64_t *var1 = malloc(sizeof(uint64_t)); /* Allocate memory for one uint64_t on the heap and set var1 to point at it */. Horizontal and vertical centering in xltabular. This means one of two things: In this particular case, you're explicitly setting a_ptr to the address of a variable, so it can't possibly be NULL at that point. It would be tricky, and they would want WG14 (C working group) to at least bless this change, and more likely, make the analogous change to the C standard. However there is no portable way to verify that the pointer is valid, other than checking for null. Class - a weakness that is described in a very abstract fashion, typically independent of any specific language or technology. Without coverity i probably would not have found this copy&paste error. Not the answer you're looking for? The article easily misleads the reader into believeing that ensuring pointer validity boils down to checking for pointer being not equal to NULL. For users who wish to see all available information for the CWE/CAPEC entry. First if executes for cond1 and else executes for cond2.. Only one of them could be true at a time. Many modern techniques use data flow analysis to minimize the number of false positives. How come an array's address is equal to its value in C? Your assertion is not backed by the wording in the standard, nor by common implementer understanding. but we still consider it a violation of this rule for practicality, although to be anal, it is instead a violation of ARR30-C. NIST Workshop on Software Security Assurance Tools Techniques and Metrics. There are other problems with this code, as is noted in the rule. In this scenario, by the time, I come in 'cond2', I already have 'q' set. mruby is vulnerable to NULL Pointer. The platform does add offsetof( struct_type, member) to input and dereferences that. What's the cheapest way to buy out a sibling's share of our parents house if I have no cash and want to pay less than the appraised value? NULL can't point to data. rev2023.5.1.43405. Why does the second compliant example permit using possibly-null pointers? Allocated memory leaked in several cases. Since SIZE_MAX represents the largest possible object, the largest possible string would then be SIZE_MAX-1 characters long (excluding '\0'). In addition, relationships such as PeerOf and CanAlsoBe are defined to show similar weaknesses that the user may want to explore. The added benefit of this is that you probably no longer require both p and q and so the entire function becomes far more lean. Solution 1, it looks like, today's solution tomorrow's problem. In the complaint version, I like to make source code checking a little quicker by putting parenthesizes around arguments to |= or &= as. On such a call, a function that locates a character finds no occurrence, a function that compares two character sequences returns zero, and a function that copies characters copies zero characters. It also reinforces the notion to the reader that any time you see arithmetic in an allocation expression, you need to think about corner-cases. Configure coverity to check that a declared variable is initialized before usage as a pointer. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. So let me be more precise in my wording: I assert that a platform whose memcpy() did anything besides copy zero bytes when given n=0 and valid src and dest pointers was not C-standards-compliant. The Phase identifies a point in the life cycle at which introduction may occur, while the Note provides a typical scenario related to introduction during the given phase. Markus:AFAICT the respponses to this StackOverflow question agree with my previous assertions. unity3d - C# Coverity giving "Dereference before null check (REVERSE How do the interferometers on the drag-free satellite LISA receive power without altering their geodesic trajectory? Embedded hyperlinks in a thesis or research paper. Class level weaknesses typically describe issues in terms of 1 or 2 of the following dimensions: behavior, property, and resource. Chain - a Compound Element that is a sequence of two or more separate weaknesses that can be closely linked together within software. Not the answer you're looking for? Coverity issue : Explicit Null dereferenced, How a top-ranked engineering school reimagined CS curriculum (Ep. This bug ONLY surfaces when debugging or running the program with her verbosity. Monitor the software for any unexpected behavior. Why does Acts not mention the deaths of Peter and Paul? To subscribe to this RSS feed, copy and paste this URL into your RSS reader. Content Discovery initiative April 13 update: Related questions using a Review our technical responses for the 2023 Developer Survey, Using LINQ to remove elements from a List. Example: educators, technical writers, and project/program managers. Unless explicitly stated otherwise in the description of a particular function in this subclause, pointer arguments on such a call shall still have valid values, as described in 7.1.4. A NULL pointer dereference occurs when the application dereferences a pointer that it expects to be valid, but is NULL, typically causing a crash or exit. That exception could have rendered the entire feature non operational (And many log messages that the user wouldn't understand). A pointer should be made to point to some valid memory location before writing something to it. I believe in this case, either expression would work. Not the answer you're looking for? CVE-2023-1587 : Avast and AVG Antivirus for Windows were susceptible to uint64_t *var1 = NULL; this declares a uint64_t pointer (type uint64_t*). This pointer was the resaon of a memory leak Realy nice catch by Coverity. that we haven't considered here: I'd guess null pointers are not valid, even though they point to 0 bytes. Did the drapes in old theatres actually say "ASBESTOS" on them? FWIW the pointer arithmetic is also invalid because p1 does not point to valid memory, so you scan't just say something like, That code does not violate th is rule, but it violates ARR30-C. Do not form or use out-of-bounds pointers or array subscripts. This compliant solution ensures that both input_str andthe pointer returned by malloc() are not null: This noncompliant code example is from a version of drivers/net/tun.c and affects Linux kernel 2.6.30 [Goodin 2009]: The sk pointer is initialized to tun->sk before checking if tun is a null pointer. Copy & paste errors might not often cause system crashes, but developer headaches. The issue was fixed with Avast and AVG Antivirus version 22.11 Publish Date : 2023-04-19 Last Update Date : 2023-04-19 Collapse All Expand All Select Select&Copy Scroll To Vendor . Security Intelligence; Non-intrusive assessment; Developers SDK; Database . I'll just provide a few references to back up my beliefs. Standing by. Asking for help, clarification, or responding to other answers. In this case, the difference is the assumption thatmalloc() always returns non-nullfor the second NCCE, whereas the first NCCE has themalloc() abstracted away. What REALLY happens when you don't free after malloc before program termination? It evaluates to true if a_ptr is not NULL. * @param affinityGroup broken affinity rule CWE is sponsored by the U.S. Department of Homeland Security (DHS) Cybersecurity and Infrastructure Security Agency (CISA) and managed by the Homeland Security Systems Engineering and Development Institute (HSSEDI) which is operated by The MITRE Corporation (MITRE). Otherwise, the result is a pointer to the object or function designated by its operand. In this scenario, by the time, I come in 'cond2', I already have 'q' set. Asking for help, clarification, or responding to other answers. My guess is it is telling you "you are doing the NULL check now, but you have already dereferenced it before. in this line you are trying to assign a value 0 to a location pointed by var1 which is NUll location ie invalid address and de-referencing a invalid /Null address will result in crash. Find centralized, trusted content and collaborate around the technologies you use most. May it be expected that the address of operator will eventually be evaluated only after a pointer dereference for a desirable access to a data structure member? I'd guess WG14 has considered these questions, but I haven't until now :). It looks like a logic bug, which can cause a memory leaking. Thanks for contributing an answer to Stack Overflow! Could I capture, and I would be able to glean much security information from the dump? Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. Not the answer you're looking for? It is pretty easy to miss such things when adding a new feature. That's true. I would also guess that pointers that point to the one-past-the-end of an array are also invalid. {"serverDuration": 277, "requestCorrelationId": "e2a1d936a1543fbd"}, EXP34-C. Do not dereference null pointers, Clever Attack Exploits Fully-Patched Linux Kernel, ERR33-C. Detect and handle standard library errors, one compliant and one non-compliant example, CERT Oracle Secure Coding Standard for Java, EXP01-J. It is kind of funny, though. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. Improve INSERT-per-second performance of SQLite. I think that checking for user_data being NULL would be an improvement to the CS so long as there is an explicit mention that user_data being NULL is invalid even if length == 0. It even looked as a false positive at first. Found logically dead code that would never have been accessed. When c_str is dereferenced in memcpy(), the program exhibits undefined behavior. Unfortunately, your link also points to code that violates this rule, and is thus undefined behavior. ', referring to the nuclear power plant in Ignalina, mean? Coverity scan helps our developers finding issues like these. 33615. The choice could be made to use a language that is not susceptible to these issues. Coverity is correctly telling you that, albeit in a somewhat indirect way. To fix the bug in the code and also make Coverity happy, as suggested by derHugo in a comment, change the RemoveAll line to something like this: Thanks for contributing an answer to Stack Overflow! You need to show more code along with what static analysis tool you are using for us to be able to give an answer to you. This noncompliant code example is derived from a real-world example taken from a vulnerable version of the libpng library as deployed on a popular ARM-based cell phone [Jack 2007]. And in this step. Yes the ordering matters. The different Modes of Introduction provide information about how and when this weakness may be introduced. Consider the following example of a typical client server exchange. The chunkdata pointer is later used as a destination argument in a call to memcpy(), resulting in user-defined data overwriting memory starting at address 0. Clearly the standard enumerates 1 case of undefined behavior, but makes no special mention of n=0. Hence the error. Null pointer dereferences: This code will definitely crash due to a null pointer dereference in certain cases.. View Defect : wazuh/ossec-wazuh: USE_AFTER_FREE: C/C++: Memory - illegal accesses: This pointer was the resaon of a memory leak. The above check can't hurt, as I guess you could have a system with a 32-bit size_t that had a ton of memory and had some crazy banking/selector scheme with pointers. The return value from strchr() is often NULL, but the dev might know that a specific strchr() function call will not return NULL. Solutions I propose: .. It modifies the pointed-to data. first, a null assignment, or a comparison with null will give Coverity an evidence to believe the variable could be null. If your code examples are simply searching for instances of C code of this nature, then the UB is not in your code, you just may be searching for code with potential UB. When this happens, CWE refers to X as "primary" to Y, and Y is "resultant" from X. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide, Not sure if this is directly related to the error/warning you get but in general I think you should rather use, C# Coverity giving "Dereference before null check (REVERSE_INULL)" on a RemoveAll call to remove null entries from a list, How a top-ranked engineering school reimagined CS curriculum (Ep. CWE - CWE-476: NULL Pointer Dereference (4.11) - Mitre Corporation 2005. More information is available Please edit the custom filter or select a different filter. Interpreting non-statistically significant results: Do we have "no evidence" or "insufficient evidence" to reject the null? Variant level weaknesses typically describe issues in terms of 3 to 5 of the following dimensions: behavior, property, technology, language, and resource. There are only two condidtions in my code, cond1 and cond2. Since the code does not check the return value from gethostbyaddr (CWE-252), a NULL pointer dereference (CWE-476) would then occur in the call to strcpy(). See "Clever Attack Exploits Fully-Patched Linux Kernel" [Goodin 2009] for an example of a code execution exploit that resulted from a null pointer dereference. What is this brick with a round back and a stud on the side used for? Copy the n-largest files from a certain directory to the current one. It would cause game actors to teleport to the wrong coordinates. very useful to find this very horrible bug in this case, we're using a pointer to memory which is not guaranteed to be zero, and potentially corrupting the malloc arena in the process. I have the following section of code, which gives explicit null dereferenced. If you trigger an unhandled exception or similar error that was discovered and handled by the application's environment, it may still indicate unexpected conditions that were not handled by the application itself. This one is pretty awesome. Which ensures that the chunkdata pointer is valid, but makes no such check to the user_data pointer. CWE, CWSS, CWRAF, and the CWE logo are trademarks of The MITRE Corporation. Agreed. Furthermore, the C++20 draft (N4860) s7.6.2.1p1 says: The unary * operator performs indirection: the expression to which it is applied shall be a pointer to an object type, or a pointer to a function type and the result is an lvalue referring to the object or function to which the expression points. If you are working with a multithreaded or otherwise asynchronous environment, ensure that proper locking APIs are used to lock before the if statement; and unlock when it has finished. which bolsters my assertion that x->member dereferences x (or at least an offset of x). View Defect : ScummVM: OVERRUN: C/C++: Memory - illegal accesses: Realy nice catch by Coverity. Fixed by setting name to Oh joy. Dereferencing a pointer that might be null " findVmViolatingPositiveAg(affinityGroup, vmToHost) " when calling " getVmsByIds . 0 is a valid value as far as memcpy() is concerned, and malloc() has special language concerning malloc(0). I would never have thought of looking at this piece of code if coverity hadn't found it. Each call of the impacted function may consumes many bytes (it's a file path). Connect and share knowledge within a single location that is structured and easy to search. Would you become interested in a related clarification approach for a discussion topic like . .. Would it be ok if I write !cond1 just like this: Logically, based on what you've said, and assuming that code1 and code2 are mutually exclusive, this is a false positive. In the following code, the programmer assumes that the system always has a property named "cmd" defined. It does not give the pointer a new value. accesses memory stored at its address. In the first compliant example it's useless to do allocation if the essential pointer user_data is NULL. That makes sense. The value 0 for the number of bytes to copy is not what causes the UB, it's the null pointer value which triggers it. You probably don't understand that the * in a pointer declaration and the * in a pointer arithmetics expression mean completely opposite things. SIZE_MAX is the largest possible value that a size_t could take, so it is not possible to have anything larger than SIZE_MAX. void host_lookup(char *user_supplied_addr){, if("com.example.URLHandler.openURL".equals(intent.getAction())) {. Adding EV Charger (100A) in secondary panel (100A) fed off main (200A), Are these quarters notes or just eighth notes? Why the obscure but specific description of Jane Doe II in the original complaint for Westenbroek v. Kappa Kappa Gamma Fraternity? The two languages try to maximize compatibility, and occasionally succeed. When the URL is not present, the call to getStringExtra() will return null, thus causing a null pointer exception when length() is called. To learn more, see our tips on writing great answers. Content Discovery initiative April 13 update: Related questions using a Review our technical responses for the 2023 Developer Survey. Is it safe to publish research papers in cooperation with Russian academics? To subscribe to this RSS feed, copy and paste this URL into your RSS reader. Coverity complains below message: I do not understand why coverity complains here. Relatively low, but also relatively hilarious - someone decided to "shut up" a GCC warning in 2006 by putting parentheses around an assignment used as a truth value, but misplaced Impact is low, just wanted to commend you! The HandleRequest function is intended to perform a request and use a defer to close the connection whenever the function returns. is undefined behavior (UB) if input does not actually point to a valid struct. It should be an ingrained practice. *var1 = 0; this dereferences the pointer, i.e. parsing /proc/self/maps under linux) one might find out whether the pointer points into mapped memory, but this is still not a guarantee of validity because it is very coarse-grained see again the above example. In particular, this paragraph enables & to cancel out * (eg &*x == x) and [] (eg &x[5] == x + 5), but not ->. Isn't easier just to check valid range of length? The standard will simply copy 0 byteswhich is essentially a no-op. Making statements based on opinion; back them up with references or personal experience. Would My Planets Blue Sun Kill Earth-Life? Using platform-specific means (e.g. NULL Pointer Dereference in mrb_vm_exec with super in These may be for specific named Languages, Operating Systems, Architectures, Paradigms, Technologies, or a class of such platforms. Dereferencing a null pointer is undefined behavior. What is it that I did not understand? I would therefore assert that a platform whose memcpy() did anything besides a no-op when given n=0 and valid source/destination pointers was not C-standards-compliant. Network monitor allows remote attackers to cause a denial of service (crash) or execute arbitrary code via malformed packets that cause a NULL pointer dereference. The n=0 is a mildly interesting edge case: Clearly a pointer that points to at least one valid byte could be used as the src or dest pointer to a call to memcpy(, 0). The description The sk pointer is initialized to tun->sk before checking if tun is a null pointer. is provided for a non-compliant code example.Thus it seems that the arrow operator (member access through pointer) is usually treated also as a dereference operation.

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