Copyright 20062023, The MITRE Corporation. When c_str is dereferenced in memcpy(), the program exhibits undefined behavior. Game allows remote attackers to cause a denial of service (server crash) via a missing argument, which triggers a null pointer dereference. And in this case, there is no pointed-to data. Isn't easier just to check valid range of length? As a result, this noncompliant code example is vulnerable to a null pointer dereference exploit, because null pointer dereferencing can be permitted on several platforms, for example, by using mmap(2) with the MAP_FIXED flag on Linux and Mac OS X, or by using the shmat() POSIX function with the SHM_RND flag [Liu 2009]. rev2023.5.1.43405. This compliant solution ensures that the pointer returned by png_malloc() is not null. Additionally, if input_str is a null pointer, the call to strlen() dereferences a null pointer, also resulting in undefined behavior. Could a subterranean river or aquifer generate enough continuous momentum to power a waterwheel for the purpose of producing electricity? 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 libpng library implements its own wrapper to malloc() that returns a null pointer on error or on being passed a 0-byte-length argument. If you don't set it again before the above if statement, that means that the NULL check is unnecessary and should be removed. No affinity group collision detected for cluster {}. I reordered that code example to do all the checks before allocations. . This MemberOf Relationships table shows additional CWE Categories and Views that reference this weakness as a member. Can I use the spell Immovable Object to create a castle which floats above the clouds? 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. Clearly the standard enumerates 1 case of undefined behavior, but makes no special mention of n=0. Thanks for the reference to Julia Lawall's response to your question. 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. The standard will simply copy 0 byteswhich is essentially a no-op. Note that this code is also vulnerable to a buffer overflow (CWE-119). 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. Solutions I propose: .. void host_lookup(char *user_supplied_addr){, if("com.example.URLHandler.openURL".equals(intent.getAction())) {. uint64_t *var1 = NULL; this declares a uint64_t pointer (type uint64_t*). This is in the key management code which converts passwords. I find it interesting in this case how you think in another direction. But no where in that particular idiom would a NULL pointer necessarily be deferenced. Example: educators, technical writers, and project/program managers. This HandleRequest Function evaluates the close before checking the error. This was potentially problematic, due to the assert on an uninitialized variable. This code also violates ERR33-C. Detect and handle standard library errors. Overall, I disagree with her answer, and agree with the StackOverflow response (https://stackoverflow.com/questions/25725286/does-taking-address-of-member-variable-through-a-null-pointer-yield-undefined-be). 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). Buffer overflow and possibly corrupting the module database. Note that it doesn't know how to check for non-heap, non-stack. .. 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. How do the interferometers on the drag-free satellite LISA receive power without altering their geodesic trajectory? Buffer overflow difficult to find by reading the code that would result a crash if path is too long. 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. Is this a false positive from Coverity or should I do something to fix this? Did the drapes in old theatres actually say "ASBESTOS" on them? The libpng library allows applications to read, create, and manipulate PNG (Portable Network Graphics) raster image files. Is it safe to publish research papers in cooperation with Russian academics? And the compliant solution guarantees that the pointer will be valid if the code calls memcpy(). An extremely nice thing which was discovered only by Coverity. cov-analyze scan is returning Reverse NULL and Customer believes Coverity is reporting false positive "Dereference before NULL check". <, [REF-18] Secure Software, Inc.. "The CLASP Application Security Process". It seems that my understanding needs also to grow for such information. SSL software allows remote attackers to cause a denial of service (crash) via a crafted SSL/TLS handshake that triggers a null dereference. In particular, this paragraph enables & to cancel out * (eg &*x == x) and [] (eg &x[5] == x + 5), but not ->. Right? Before assigning a value you need to allocate a memory and make the pointers to point to that memory location and then assign a value. 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. This bug was quite hard to spot! NULL can't point to data. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. "Signpost" puzzle from Tatham's collection. If input is null, that is technically not a null dereference. This code also violates ERR33-C. Detect and handle standard library errors. View - a subset of CWE entries that provides a way of examining CWE content. In addition, relationships such as PeerOf and CanAlsoBe are defined to show similar weaknesses that the user may want to explore. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. More specific than a Base weakness. Why the obscure but specific description of Jane Doe II in the original complaint for Westenbroek v. Kappa Kappa Gamma Fraternity? Alternate Terms Relationships Asking for help, clarification, or responding to other answers. Thanks! Aaron:I suspect we are talking past each other. Simple deform modifier is deforming my object, xcolor: How to get the complementary color. /** and Gary McGraw. Would such an aspect be influenced in any ways if the address of operator would be applied around similar expressions? This is not a perfect solution, since 100% accuracy and coverage are not feasible. OS allows remote attackers to cause a denial of service (crash from null dereference) or execute arbitrary code via a crafted request during authentication protocol selection. Thus I became a bit more curious about involved technical details. This is a matter of style, and also following code walkthrough. In your code example, the p1my_item will be evaluated before t he & operator, and so this rule is violated, although you are really trying to do pointer arithmetic rather than see what the pointer points to. 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(). <<< 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. accesses memory stored at its address. Coverity issue : Explicit Null dereferenced, How a top-ranked engineering school reimagined CS curriculum (Ep. 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. Note that 7.1.4 explicitly states that a null pointer is not a valid pointer argument. Among the invalid values for dereferencing a pointer by the unary * operator are a null pointer, an address inappropriately aligned for the type of object pointed to, and the address of an object after the end of its lifetime. 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. Not the answer you're looking for? And this error has been in the codebase for the last 9 Coverty scan correctly understood the logic of this code, and reported that the loop condition is wrong. * @param vmToHost vm to host assignments To learn more, see our tips on writing great answers. Avast and AVG Antivirus for Windows were susceptible to a NULL pointer dereference issue via RPC-interface. Dates. But passing 0 to memcpy() is not one of them. Making statements based on opinion; back them up with references or personal experience. Best to cite C11 s7.24.2.1 here: The memcpy function copies n characters from the object pointed to by s2 into the object pointed to by s1. "Seven Pernicious Kingdoms: A Taxonomy of Software Security Errors". Making statements based on opinion; back them up with references or personal experience. 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. Improve INSERT-per-second performance of SQLite. 2005-11-07. This means one of two things: 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. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. The code is dead and will be never processed because 'decoded' outside the scope and redefined in local. It also permits &x[y] to translate to x + y, but that is still UB if x is null because of ARR38-C. ISO C just has no similar wording for x->member. you are trying to make your var1 to point to the same location as that of var2 and casting it to uint64_t.So from the above two sections var1 and var2 are pointing to NULL pointer ie nothing in simple terms. Example: tool developers, security researchers. While not explicitly mentioning UB, I would infer that *NULL is UB since NULL is not a pointer to an object or function type. Server allows remote attackers to cause a denial of service (crash) via malformed requests that trigger a null dereference. Event var_deref_model: | Passing null pointer "master_uri_env" to "operator =", which dereferences it. 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? Coverity is giving you a warning because you are in fact doing a NULL check: Here, a_ptr is evaluated in a boolean context. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. The final NCCE is actually more insidious than it seems at first. ssh component for Go allows clients to cause a denial of service (nil pointer dereference) against SSH servers. This bug ONLY surfaces when debugging or running the program with her verbosity. ', referring to the nuclear power plant in Ignalina, mean? Thanks, David! 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. *var1 = 0; this dereferences the pointer, i.e. If the operand has type "type", the result has type "pointer to type". It is kind of funny, though. Since SIZE_MAX represents the largest possible object, the largest possible string would then be SIZE_MAX-1 characters long (excluding '\0'). It does not give the pointer a new value. See C23 (n3096) s6.5.3.2p3: The unary & operator yields the address of its operand. Typical "easy to spot if you know there is a problem error". Why is this error being shown and is there a way to correct it? ), 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. How to force Unity Editor/TestRunner to run at full speed when in background? Example: tool developers, security researchers, pen-testers, incident response analysts. Optimizers are optimizing based on this latitude and have been for years. Expressions (EXP), SEI CERT C Coding Standard - Guidelines 03. In particular, ROSE ensures that any pointer returned by malloc(), calloc(), or realloc() is first checked for NULL before being used (otherwise, it is free()-ed). I've changed it to say null pointer instead of invalid pointer. I'd guess WG14 has considered these questions, but I haven't until now :). 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 . of making the mruby interpreter crash, thus affecting the. is undefined behavior (UB) if input does not actually point to a valid struct. Synopsys, Inc. | Policy Statement | Contact. There are only two condidtions in my code, cond1 and cond2. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide, Asside - I would suggest initialising your pointers to, It's impossible to tell from that code whether. The Scope identifies the application security area that is violated, while the Impact describes the negative technical impact that arises if an adversary succeeds in exploiting this weakness. More specific than a Pillar Weakness, but more general than a Base Weakness. return p == NULL || (char *)p < &_etext; One situation this can happen is when the pointer has been checked against NULL and is dereferenced later.

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