CVE-2024-50186

In the Linux kernel, the following vulnerability has been resolved:

net: explicitly clear the sk pointer, when pf->create fails

We have recently noticed the exact same KASAN splat as in commit 6cd4a78d962b (net: do not leave a dangling sk pointer, when socket creation fails). The problem is that commit did not fully address the problem, as some pf->create implementations do not use sk_common_release in their error paths.

For example, we can use the same reproducer as in the above commit, but changing ping to arping. arping uses AF_PACKET socket and if packet_create fails, it will just sk_free the allocated sk object.

While we could chase all the pf->create implementations and make sure they NULL the freed sk object on error from the socket, we cant guarantee future protocols will not make the same mistake.

So it is easier to just explicitly NULL the sk pointer upon return from pf->create in __sock_create. We do know that pf->create always releases the allocated sk object on error, so if the pointer is not NULL, it is definitely dangling.

Weakness

Referencing memory after it has been freed can cause a program to crash, use unexpected values, or execute code.

Affected Software

Extended Description

The use of previously-freed memory can have any number of adverse consequences, ranging from the corruption of valid data to the execution of arbitrary code, depending on the instantiation and timing of the flaw. The simplest way data corruption may occur involves the system’s reuse of the freed memory. Use-after-free errors have two common and sometimes overlapping causes:

In this scenario, the memory in question is allocated to another pointer validly at some point after it has been freed. The original pointer to the freed memory is used again and points to somewhere within the new allocation. As the data is changed, it corrupts the validly used memory; this induces undefined behavior in the process. If the newly allocated data happens to hold a class, in C++ for example, various function pointers may be scattered within the heap data. If one of these function pointers is overwritten with an address to valid shellcode, execution of arbitrary code can be achieved.

Potential Mitigations

References

• https://git.kernel.org/stable/c/563e6892e21d6ecabdf62103fc4e7b326d212334
• https://git.kernel.org/stable/c/631083143315d1b192bd7d915b967b37819e88ea
• https://git.kernel.org/stable/c/8e1b72fd74bf9da3b099d09857f4e7f114f38e12
• https://git.kernel.org/stable/c/b7d22a79ff4e962b8af5ffe623abd1d6c179eb9f
• https://git.kernel.org/stable/c/daf462ff3cde6ecf22b98d9ae770232c10d28de2