By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. I say "theoretical" because I have not successfully produced strings of this length in testing. valgrind wasnt that usefull because of its slowness. Horizontal and vertical centering in xltabular. 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. http://blog.llvm.org/2011/05/what-every-c-programmer-should-know_14.html. Base - a weakness cov-analyze scan is returning Reverse NULL and Customer believes Coverity is reporting false positive "Dereference before NULL check". * @param affinityGroup broken affinity rule Could a subterranean river or aquifer generate enough continuous momentum to power a waterwheel for the purpose of producing electricity? NULL pointer dereferences usually result in the failure of the process unless exception handling (on some platforms) is available and implemented. Embedded hyperlinks in a thesis or research paper, Adding EV Charger (100A) in secondary panel (100A) fed off main (200A). 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. but we still consider it a violation of this rule for practicality, although to be anal, it is instead a violation of ARR30-C. A deferred call's arguments are evaluated immediately, so the defer statement panics due to a nil response. Variant level weaknesses typically describe issues in terms of 3 to 5 of the following dimensions: behavior, property, technology, language, and resource. This warning thrown by Coverity if you dereference a pointer and then later on do a NULL check on it. The sk pointer is initialized to tun->sk before checking if tun is a null pointer. first, a null assignment, or a comparison with null will give Coverity an evidence to believe the variable could be null. race condition causes a table to be corrupted if a timer activates while it is being modified, leading to resultant NULL dereference; also involves locking. In the case of the ARM and XScale architectures, the 0x0 address is mapped in memory and serves as the exception vector table; consequently, dereferencing 0x0 did not cause an abnormal program termination. Whoops, you're right. The pointer could in fact be NULL and any dereference prior to that NULL check could result in a NULL pointer dereference, so you need to either do the NULL check sooner or don't deereference at that point. Coverity is correctly telling you that, albeit in a somewhat indirect way. Could a subterranean river or aquifer generate enough continuous momentum to power a waterwheel for the purpose of producing electricity? I'd guess WG14 has considered these questions, but I haven't until now :). Find centralized, trusted content and collaborate around the technologies you use most. Is there any known 80-bit collision attack? rev2023.5.1.43405. Alternate Terms Relationships Avast and AVG Antivirus for Windows were susceptible to a NULL pointer dereference issue via RPC-interface. Why does this example of what compilers aren't allowed to do cause null pointer dereferencing using cmov? So we have to check all the arguments before performing any actions. 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. Copyright 20062023, The MITRE Corporation. Do you find another previous clarification approach interesting and helpful? The 4gig boundary will probably be important too with unsigned int in LP64, but since size_t will be 64-bit, there will have to be some truncation that compilers will be able to warn on. A Community-Developed List of Software & Hardware Weakness Types, Technical Impact: DoS: Crash, Exit, or Restart, Technical Impact: Execute Unauthorized Code or Commands; Read Memory; Modify Memory. The standard will simply copy 0 byteswhich is essentially a no-op. Customer's opinion is that it is always a good practice to check a pointer for a NULL Value before freeing it. The correct idiom is to only allocate storage if the pointer is currently NULL. EXP34-C is a common consequence of ignoring function return values, but it is a distinct error, and can occur in other scenarios too. Markus:AFAICT the respponses to this StackOverflow question agree with my previous assertions. 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. It is always true that if E is a function designator or an lvalue that is a valid operand of the unary & operator, *&E is a function designator or an lvalue equal to E. If *P is an lvalue and T is the name of an object pointer type, *(T)P is an lvalue that has a type compatible with that to which T points. Checker. 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 . Is this a false positive from Coverity or should I do something to fix this? Allowing it to be removed. ), [REF-6] Katrina Tsipenyuk, Brian Chess Identify error conditions that are not likely to occur during normal usage and trigger them. My guess is it is telling you "you are doing the NULL check now, but you have already dereferenced it before. 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. If an attacker provides an address that appears to be well-formed, but the address does not resolve to a hostname, then the call to gethostbyaddr() will return NULL. Thanks for contributing an answer to Stack Overflow! C/C++ Dereference error: Dereference before null check, Solving C warning - dereferencing a null pointer. 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). This compliant solution ensures that the pointer returned by png_malloc() is not null. I would, at the very least, put an assert(q) inside if (code2), but: Ideally you'd stick with that one if/else and put all your logic in there. Configure coverity to check that a declared variable is initialized before usage as a pointer. If input is null, that is technically not a null dereference, but we still consider it a violation of this rule for practicality, although to be anal, it is instead a violation of ARR30-C. While not explicitly mentioning UB, I would infer that *NULL is UB since NULL is not a pointer to an object or function type. In Xcode 9 and later, you can use this check to detect the creation of null references and null pointer dereferences. This check identifies such situation by checking all possible paths where such NULL dereferences can occur. Find centralized, trusted content and collaborate around the technologies you use most. Right? There are only two condidtions in my code, cond1 and cond2. that is linked to a certain type of product, typically involving a specific language or technology. I believe that dereferencing NULL should not crash the system, should not allow a write to a NULL pointer area, but should always set errno, If I am a hacker, could I trap a null failure that would force a memory dump. Possible Null Pointer exception was found in a feature in which I'm the feature owner. Iflengthhas the value1, the addition yields 0, and png_malloc() subsequently returns a null pointer, which is assigned to chunkdata. Even when exception handling is being used, it can still be very difficult to return the software to a safe state of operation. If you don't set it again before the above if statement, that means that the NULL check is unnecessary and should be removed. It should be an ingrained practice. If the compiler finds a pointer dereference, it treats that pointer as nonnull. The two main view structures are Slices (flat lists) and Graphs (containing relationships between entries). This code will definitely crash due to a null pointer dereference in certain cases. uint64_t *var1 = malloc(sizeof(uint64_t)); /* Allocate memory for one uint64_t on the heap and set var1 to point at it */. This HandleRequest Function evaluates the close before checking the error. Simple deform modifier is deforming my object, xcolor: How to get the complementary color. Solution 1, it looks like, today's solution tomorrow's problem. Thanks for this checker. That exception could have rendered the entire feature non operational (And many log messages that Unused value and previous write overwriting found in the defect meant error in algorithm. Coverity found a case where a copy/paste action went wrong. One of the Coccinelle software maintainers expressed opposite development views today. The issue is: memcpy() and friends do not explicitly state that a null pointer is a valid pointer value, even if the number of bytes to copy is 0. The code is dead and will be never processed because 'decoded' outside the scope and redefined in local. What are the advantages of running a power tool on 240 V vs 120 V? Variable "var" was uninitialized, then function that was supposed to fill it in was called. In that case, if you want to change the value of the pointed-to data, well, have the pointer point to some writeable memory first! What is the symbol (which looks similar to an equals sign) called? Thanks for contributing an answer to Stack Overflow! Your assertion is not backed by the wording in the standard, nor by common implementer understanding. The test was added to catch the possibly theoretical situation where the length of input_str was somehow the maximum size for size_t, and adding one to this size in the malloc expression (to allocated space for the trailing null byte) results in an integer overflow. extern char _etext; 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. assert(!invalid(p)); // or whatever, bool invalid(const void *p) { Software Engineering Institute This code also violates ERR33-C. Detect and handle standard library errors. Additionally, if input_str is a null pointer, the call to strlen() dereferences a null pointer, also resulting in undefined behavior. However, I must add a few qualifications: First of all, there is the question of whether this is for C or for C++. @HemantBhargava - you may know that, but the code you have shown us does not ensure that.
