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. * Select VMs from the broken affinity group that are running on the same host. In particular, this paragraph enables & to cancel out * (eg &*x == x) and [] (eg &x[5] == x + 5), but not ->. Variable "var" was uninitialized, then function that was supposed to fill it in was called. Do you find another previous clarification approach interesting and helpful? But passing 0 to memcpy() is not one of them. Assign an array of Swift strings to a C structure variable taking a char ** value. That noncompliant code example (it's currently the 3rd) came from the Linux kernel, whose source is publicly available. More specific than a Pillar Weakness, but more general than a Base Weakness. Class - a weakness that is described in a very abstract fashion, typically independent of any specific language or technology. There are other problems with this code, as is noted in the rule. Made code more compliant with other rules. 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. This defect on our template caused null pointer deferencing in over hundred use cases. The return value from strchr() is often NULL, but the dev might know that a specific strchr() function call will not return NULL. Making statements based on opinion; back them up with references or personal experience. 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. That's true. I suppose we can check that that is not null, but we cannot check that it is valid (in any portable way). It does not give the pointer a new value. This check identifies such situation by checking all possible paths where such NULL dereferences can occur. 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! 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. Why the obscure but specific description of Jane Doe II in the original complaint for Westenbroek v. Kappa Kappa Gamma Fraternity? At this point we define size as strlen(input_str) + 1. I have the following section of code, which gives explicit null dereferenced. This fault is buried deep within some complex logic that makes it really hard to track. . But no where in that particular idiom would a NULL pointer necessarily be deferenced. This solution also ensures that theuser_data pointer is not null. These types of problems usually lead to insidious correctness errors since exceptions are caught at a higher level. Generating points along line with specifying the origin of point generation in QGIS. Is there any known 80-bit collision attack? To subscribe to this RSS feed, copy and paste this URL into your RSS reader. 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. For users who wish to see all available information for the CWE/CAPEC entry. Did the drapes in old theatres actually say "ASBESTOS" on them? Why don't we use the 7805 for car phone chargers? I would also guess that pointers that point to the one-past-the-end of an array are also invalid. Possible Null Pointer exception was found in a feature in which I'm the feature owner. Thanks for the reference to Julia Lawall's response to your question. Small typo nit: "such as if i t pointed to freed memory" meant to say "if it" instead (removing whitespace). It is pretty easy to miss such things when adding a new feature. mruby is vulnerable to NULL Pointer. Yes the ordering matters. I note with interest, that ISO C does permit &*x when x is null. The code is dead and will be never processed because 'decoded' outside the scope and redefined in local. 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. It modifies the pointed-to data. The two languages try to maximize compatibility, and occasionally succeed. If you want to change the value of your pointer, just do. DATABASE RESOURCES PRICING ABOUT US. 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]. The platform does add offsetof( struct_type, member) to input and dereferences that. :). So the SIZE_MAX check was unnecessary. C/C++ Dereference error: Dereference before null check, Solving C warning - dereferencing a null pointer. Consider the following example of a typical client server exchange. Finally, Clang and Coccinelle are part of the LLVM project, which will define some of the undefined behaviors in C++. That makes sense. These relationships are defined as ChildOf, ParentOf, MemberOf and give insight to similar items that may exist at higher and lower levels of abstraction. What are the arguments for/against anonymous authorship of the Gospels, Two MacBook Pro with same model number (A1286) but different year, Simple deform modifier is deforming my object. 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. It can never evaluate to true (unless Equals has been overridden to do something screwy). What is it that I did not understand? Use of the Common Weakness Enumeration (CWE) and the associated references from this website are subject to the Terms of Use. But the problem also exists in the compliant version, so I'm not so sure that it's really compliant. Coverity is correctly telling you that, albeit in a somewhat indirect way. And in this case, there is no pointed-to data. Solutions I propose: .. Alternate Terms Relationships 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. 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. that is linked to a certain type of product, typically involving a specific language or technology. I'm learning and will appreciate any help, Embedded hyperlinks in a thesis or research paper. Why are players required to record the moves in World Championship Classical games? This warning thrown by Coverity if you dereference a pointer and then later on do a NULL check on it. Note that 7.1.4 explicitly states that a null pointer is not a valid pointer argument. (I think you cover that in a different rule.) It modifies the pointed-to data. This one alone We had some spurious hangs and never knew why. Dereferencing a null pointer is undefined behavior, typically abnormal program termination. Note that this code is also vulnerable to a buffer overflow (CWE-119). How to force Unity Editor/TestRunner to run at full speed when in background? This listing shows possible areas for which the given weakness could appear. <. Event var_deref_model: | Passing null pointer "master_uri_env" to "operator =", which dereferences it. Configure coverity to check that a declared variable is initialized before usage as a pointer. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. New feature implementation got stuck for days because old code had obscure implementation which caused debuging nightmare. 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. Can this be fixed if I reassign the *var1 to NULL again ?? For users who are mapping an issue to CWE/CAPEC IDs, i.e., finding the most appropriate CWE for a specific issue (e.g., a CVE record). LANG.MEM.NPDLANG.STRUCT.NTADLANG.STRUCT.UPD, Null pointer dereferenceNull test after dereferenceUnchecked parameter dereference, Can detect violations of this rule. Then we hit memcpy with length 0. Folder's list view has different sized fonts in different folders. rev2023.5.1.43405. The HandleRequest function is intended to perform a request and use a defer to close the connection whenever the function returns. Markus:Unfortunately, your link also points to code that violates this rule, and is thus undefined behavior. 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). Even documented "we don't need to care, I think" issue can become an issue when one does not check the background implementation. accesses memory stored at its address. Many platforms can support testing for those also. Are these quarters notes or just eighth notes? It is useful to have a function with portable interface but platform-dependent implementation: extern bool invalid(const void *); Off by one error: It is the third example. Asking for help, clarification, or responding to other answers. There are only two condidtions in my code, cond1 and cond2. Developer Description. Dates. In some situations, however, dereferencing a null pointer can lead to the execution of arbitrary code [Jack 2007,van Sprundel 2006]. 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. of making the mruby interpreter crash, thus affecting the. It is kind of funny, though. What REALLY happens when you don't free after malloc before program termination? Good question! Typical "easy to spot if you know there is a problem error". Pittsburgh, PA 15213-2612 We should Zoom if you wish to talk more. 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. If the operand has type "type", the result has type "pointer to type". <<< 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. If a user supplies a malformed request or violates the client policy, the Do method can return a nil response and a non-nil err. Avast and AVG Antivirus for Windows were susceptible to a NULL pointer dereference issue via RPC-interface. At best ISO C is under-specified in this regard, and perhaps should explicitly say so. I have simplified it below (with the first warning)-, The code goes on to do several operations with a_ptr. 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? For users who want to customize what details are displayed. If you don't set it again before the above if statement, that means that the NULL check is unnecessary and should be removed. If your code examples are simply searching for instances of C code of this nature. 2019-07-15. * @param affinityGroup broken affinity rule Hence the error. Unfortunately the problem is much more complex, and generally unsolvable within standard C. Consider the following example: There's no way f can check whether x points into valid memory or not. first, a null assignment, or a comparison with null will give Coverity an evidence to believe the variable could be null. 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. When the URL is not present, the call to getStringExtra() will return null, thus causing a null pointer exception when length() is called. Ah, gotcha. Otherwise, the result is a pointer to the object or function designated by its operand. In your case you are not doing it,so you have a segmentation fault(or crash) . I find it interesting in this case how you think in another direction. 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. VM {} is NOT a viable candidate for solving affinity group violation situation. 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. It would have been terrible to A simple decrement that wraps around causing an array overflow on lsm->lsm_oinfo[i[. . It calls x.Equals() a "dereference", unfortunately using C/C++ terminology (for historical reasons). This does not have any impact, because it is just an assert. NIST. valgrind wasnt that usefull because of its slowness. ssh component for Go allows clients to cause a denial of service (nil pointer dereference) against SSH servers. If the operand is the result of a unary * operator, neither that operator nor the & operator is evaluated and the result is as if both were omitted, except that the constraints on the operators still apply and the result is not an lvalue. I'm learning and will appreciate any help. Which language's style guidelines should be used when writing code that is supposed to be called from another language? 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. Dereferencing a null pointer is undefined behavior. Which ensures that the chunkdata pointer is valid, but makes no such check to the user_data pointer. Synopsys, Inc. | Policy Statement | Contact. NULL pointer dereference issues can occur through a number of flaws, including race conditions, and simple programming omissions. Making statements based on opinion; back them up with references or personal experience. This fault is buried deep within some complex logic that makes it really hard to track. 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. Why refined oil is cheaper than cold press oil? Base - a weakness Could a subterranean river or aquifer generate enough continuous momentum to power a waterwheel for the purpose of producing electricity? And the compliant solution guarantees that the pointer will be valid if the code calls memcpy(). Search for vulnerabilities resulting from the violation of this rule on the CERT website. Shouldn't the function check all pointers before dereferencing them or passing them to another function? Connect and share knowledge within a single location that is structured and easy to search. Yeah, I suspect once it's possible to allocate 2+gigs contiguously in amainstream install of a modern OS, we'll see a frenzy of new vulnerabilities come out. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. It was causing glusterd daemon crash for glusterfs. I'll add that right now, but I feel it's pointless, since it will only clutter up the question. It worked normally, but sometimes devices had cryptic types. ), 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. Solution 1, it looks like, today's solution tomorrow's problem. Software Engineering Institute I'll just provide a few references to back up my beliefs. 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. Not the answer you're looking for? 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. 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. Class level weaknesses typically describe issues in terms of 1 or 2 of the following dimensions: behavior, property, and resource. And in this case, there is no pointed-to data. Do not use a null in a case where an object is required, https://gcc.gnu.org/gcc-4.9/porting_to.html, ARR30-C. Do not form or use out-of-bounds pointers or array subscripts, Reconsidering pointer dereferences before null pointer checks (with SmPL), understand the source code search pattern, One of the Coccinelle software maintainers expressed opposite development views today, https://stackoverflow.com/questions/25725286/does-taking-address-of-member-variable-through-a-null-pointer-yield-undefined-be, Prior to 2018-01-12: CERT: Unspecified Relationship, Pointer Casting and Pointer Type Changes [HFC], Dereferencing an out-of-domain pointer [nullref], Section 5.2.18, "Null-Pointer Dereference", Dereferencing null pointers that were not returned by a function. A non-null but invalid pointer passed to memcpy() can indeed cause undefined behavior, but that is not the issue in the noncompliant codethe pointer will either be valid or null. Chain - a Compound Element that is a sequence of two or more separate weaknesses that can be closely linked together within software. Connect and share knowledge within a single location that is structured and easy to search. 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! 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. To learn more, see our tips on writing great answers. It should be an ingrained practice. When this happens, CWE refers to X as "primary" to Y, and Y is "resultant" from X. mruby is vulnerable to NULL Pointer Dereference Affected Software.