coverity null pointer dereference

The correct idiom is to only allocate storage if the pointer is currently NULL. :). Coverity is giving you a warning because you are in fact doing a NULL check: Here, a_ptr is evaluated in a boolean context. Find centralized, trusted content and collaborate around the technologies you use most. If you don't set it again before the above if statement, that means that the NULL check is unnecessary and should be removed. "Signpost" puzzle from Tatham's collection. Coverity Scan - Static Analysis Why refined oil is cheaper than cold press oil? Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. Which language's style guidelines should be used when writing code that is supposed to be called from another language? When length is zero, it is probably unusable condition for this function. Pointer members in structs are not checked. uint64_t *var1 = malloc(sizeof(uint64_t)); /* Allocate memory for one uint64_t on the heap and set var1 to point at it */. In particular, this paragraph enables & to cancel out * (eg &*x == x) and [] (eg &x[5] == x + 5), but not ->. And Coverity will tend to interpret your code rather than reading your mind. Aaron:I suspect we are talking past each other. In your case you are not doing it,so you have a segmentation fault(or crash) . A deferred call's arguments are evaluated immediately, so the defer statement panics due to a nil response. If an invalid value has been assigned to the pointer, the behavior of the unary * operator is undefined.115). SSL software allows remote attackers to cause a denial of service (crash) via a crafted SSL/TLS handshake that triggers a null dereference. Typical "easy to spot if you know there is a problem error". Key here (explains table format and definitions), EXP34-C = Union( CWE-690, list) where list =. Agreed. When c_str is dereferenced in memcpy(), the program exhibits undefined behavior. Finally, there is the matter of the compliant solution. 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. I believe in this case, either expression would work. More specific than a Pillar Weakness, but more general than a Base Weakness. 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. Generating points along line with specifying the origin of point generation in QGIS. Dereferencing a null pointer is undefined behavior. . Did the drapes in old theatres actually say "ASBESTOS" on them? By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. 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. Dates. LANG.MEM.NPDLANG.STRUCT.NTADLANG.STRUCT.UPD, Null pointer dereferenceNull test after dereferenceUnchecked parameter dereference, Can detect violations of this rule. It also uses the unsigned type size_t to pass the length parameter, ensuring that negative values are not passed to func(). 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. 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. Find centralized, trusted content and collaborate around the technologies you use most. If all pointers that could have been modified are sanity-checked previous to use, nearly all NULL pointer dereferences can be prevented. To learn more, see our tips on writing great answers. 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. The two main view structures are Slices (flat lists) and Graphs (containing relationships between entries). Thank you for the description (comments).It Cleared my doubts. In the following code, the programmer assumes that the system always has a property named "cmd" defined. Not the answer you're looking for? I have simplified it below (with the first warning)-, The code goes on to do several operations with a_ptr. Extended Description NULL pointer dereference issues can occur through a number of flaws, including race conditions, and simple programming omissions. For users who are interested in more notional aspects of a weakness. http://blog.llvm.org/2011/05/what-every-c-programmer-should-know_14.html. Would you become interested in a related clarification approach for a discussion topic like . uint64_t *var1 = NULL; this declares a uint64_t pointer (type uint64_t*). 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. 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. For users who want to customize what details are displayed. Thanks for the reference to Julia Lawall's response to your question. 2005. If code1 and code2 may both be true, though, then you do have a substantial bug here. Why are players required to record the moves in World Championship Classical games? Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. Apple. 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. 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. Use automated static analysis tools that target this type of weakness. ), [REF-6] Katrina Tsipenyuk, Brian Chess 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. Coverity complains below message: I do not understand why coverity complains here. Coverity - forward null dereference #1747 - Github Either the check against null is unnecessary, or there may be a null pointer dereference. 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. Is there any known 80-bit collision attack? Category - a CWE entry that contains a set of other entries that share a common characteristic. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. If copying takes place between objects that overlap, the behavior is undefined. Making statements based on opinion; back them up with references or personal experience. Pittsburgh, PA 15213-2612 Ah, gotcha. So we have to check all the arguments before performing any actions. Improve INSERT-per-second performance of SQLite. Why does Acts not mention the deaths of Peter and Paul? Common logic to perform in the middle? Avast and AVG Antivirus for Windows were susceptible to a NULL pointer dereference issue via RPC-interface. String URL = intent.getStringExtra("URLToOpen"); func HandleRequest(client http.Client, request *http.Request) (*http.Response, error) {. 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. I'm sorry if I have misunderstood the intent in your question. Using platform-specific means (e.g. Because null pointer dereferencing is undefined behavior, the compiler (GCC in this case) can optimize away the if (!tun) check because it is performed after tun->sk is accessed, implying that tun is non-null. Dereferencing a null pointer is undefined behavior, typically abnormal program termination. Consider the following example of a typical client server exchange. then the UB is not in your code, you just may be searching for code with potential UB. Whoops, you're right. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. Synopsys, Inc. | Policy Statement | Contact. The platform is listed along with how frequently the given weakness appears for that instance. Not the answer you're looking for? So no checking of the length is necessary (besides preventing integer overflow, which the compliant solution does). In this scenario, by the time, I come in 'cond2', I already have 'q' set. (I think you cover that in a different rule.) 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. 0 is a valid value as far as memcpy() is concerned, and malloc() has special language concerning malloc(0). Separate it into a different function that you can call. More information is available Please edit the custom filter or select a different filter. second, a de-reference of that variable. These types of problems usually lead to insidious correctness errors since exceptions are caught at a higher level. Embedded hyperlinks in a thesis or research paper, Adding EV Charger (100A) in secondary panel (100A) fed off main (200A). 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). NULL pointer dereferences usually result in the failure of the process unless exception handling (on some platforms) is available and implemented. 2021-12-15T00:00:00 Description. Image of minimal degree representation of quasisimple group unique up to conjugacy. Coverity complains below message: CID 25469 (#1 of 1): Explicit null dereferenced (FORWARD_NULL) 9. var_deref_op: Dereferencing null pointer q. I do not understand why coverity complains here. Could a subterranean river or aquifer generate enough continuous momentum to power a waterwheel for the purpose of producing electricity? What were the most popular text editors for MS-DOS in the 1980s? Software Engineering Institute Hence the error. It also adds assertions to document that certain other pointers must not be null. Server allows remote attackers to cause a denial of service (crash) via malformed requests that trigger a null dereference. Connect and share knowledge within a single location that is structured and easy to search. Description. 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. Made code more compliant with other rules. In 5e D&D and Grim Hollow, how does the Specter transformation affect a human PC in regards to the 'undead' characteristics and spells? By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. Folder's list view has different sized fonts in different folders. First if executes for cond1 and else executes for cond2.. Only one of them could be true at a time. The different Modes of Introduction provide information about how and when this weakness may be introduced. Adding EV Charger (100A) in secondary panel (100A) fed off main (200A), Are these quarters notes or just eighth notes? Note that it doesn't know how to check for non-heap, non-stack. 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. The two languages try to maximize compatibility, . For users who are concerned with the practical application and details about the nature of a weakness and how to prevent it from happening. Canadian of Polish descent travel to Poland with Canadian passport. // Find a VM that is breaking the affinityGroup and can be theoretically migrated, findVmViolatingPositiveAg(affinityGroup, vmToHost), org.ovirt.engine.core.dao.VmDaoImpl.getVmsByIds, Positive affinity group violation detected, Negative affinity group violation detected, // Test whether any migration is possible, this uses current AffinityGroup settings. Null pointer dereferences. ', referring to the nuclear power plant in Ignalina, mean? If you want to change the value of your pointer, just do var1 = 0; The sk pointer is initialized to tun->sk before checking if tun is a null pointer. In my experience, there are reasons to check for a NULL pointer other than dereferencing it. But the problem also exists in the compliant version, so I'm not so sure that it's really compliant. This error detected by CoverityScan detected a case where the driver would never run at the maximum CPI clock speed. Do you find another previous clarification approach interesting and helpful? Would you like to help any further according to different understanding and expectations for affected implementation details. This was potentially problematic, due to the assert on an uninitialized variable. 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. Class - a weakness that is described in a very abstract fashion, typically independent of any specific language or technology. The two languages try to maximize compatibility, and occasionally succeed. If the operand has type "type", the result has type "pointer to type". Yes the ordering matters. 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. The final NCCE is actually more insidious than it seems at first. The platform does add offsetof( struct_type, member) to input and dereferences that. Is "I didn't think it was serious" usually a good defence against "duty to rescue"? }. Solutions I propose: .. "Signpost" puzzle from Tatham's collection, Image of minimal degree representation of quasisimple group unique up to conjugacy. This pointer was the resaon of a memory leak Realy nice catch by Coverity. Off by one error: It is the third example. it may still not be enough to satisfy Coverity. The NULL check is unnecessary because the pointer can't be NULL, so the NULL check should be removed. Chains can involve more than two weaknesses, and in some cases, they might have a tree-like structure. Example: tool developers, security researchers. NULL Pointer Dereference in mrb_vm_exec with super in This information is often useful in understanding where a weakness fits within the context of external information sources. It is a corner case that would flash once in the blue moon - but with serious impact on the production availability. assert(!invalid(p)); // or whatever, bool invalid(const void *p) { Because null pointer dereferencing is undefined behavior, the compiler (GCC in this case) can optimize away the if (!tun) check because it is performed after tun->sk is accessed, implying that tun is non-null. *var1 = 0; this dereferences the pointer, i.e. 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. That makes sense. unity3d - C# Coverity giving "Dereference before null check (REVERSE If you want to change the value of your pointer, just do. How NULL access (FORWARD_NULL) is reported in Coverity - Synopsys Chain - a Compound Element that is a sequence of two or more separate weaknesses that can be closely linked together within software. In Coverity, FORWARD_NULL reports defects when there are enough evidences to be sure the null access will (can) happen. rev2023.5.1.43405. This fault is buried deep within some complex logic that makes it really hard to track. pointers - Getting warning - Dereferencing before possibly being null Not the answer you're looking for? Would My Planets Blue Sun Kill Earth-Life? Asking for help, clarification, or responding to other answers. Does &((struct name *)NULL -> b) cause undefined behaviour in C11? In this scenario, by the time, I come in 'cond2', I already have 'q' set. NULL pointer dereference issues can occur through a number of flaws, including race conditions, and simple programming omissions. Customer's opinion is that it is always a good practice to check a pointer for a NULL Value before freeing it. that we haven't considered here: I'd guess null pointers are not valid, even though they point to 0 bytes. This example takes an IP address from a user, verifies that it is well formed and then looks up the hostname and copies it into a buffer. 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. 2019-07-15. * @param vmToHost vm to host assignments We've been getting report on the random crashes, and here it is, the swapped check for index and actual indexed array value. 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. View Defect : ScummVM: OVERRUN: C/C++: Memory - illegal accesses: Realy nice catch by Coverity. 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. It does not give the pointer a new value. I got the impression that 31 source files of Linux modules will need further adjustments. This one is pretty awesome. <, [REF-1031] "Null pointer / Null dereferencing". Alternate Terms Relationships By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. Phew, we're agreed here. Configure coverity to check that a declared variable is initialized before usage as a pointer. Thanks! Isn't easier just to check valid range of length? NULL Pointer Dereference in mrb_vm_exec with super in GitHub. c - Coverity issue : Explicit Null dereferenced - Stack Overflow Content Discovery initiative April 13 update: Related questions using a Review our technical responses for the 2023 Developer Survey. Interpreting non-statistically significant results: Do we have "no evidence" or "insufficient evidence" to reject the null? The software's operation may slow down, but it should not become unstable, crash, or generate incorrect results.
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