CVE-2024-49854

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

block, bfq: fix uaf for accessing waker_bfqq after splitting

After commit 42c306ed7233 (block, bfq: dont break merge chain in bfq_split_bfqq()), if the current procress is the last holder of bfqq, the bfqq can be freed after bfq_split_bfqq(). Hence recored the bfqq and then access bfqq->waker_bfqq may trigger UAF. Whats more, the waker_bfqq may in the merge chain of bfqq, hence just recored waker_bfqq is still not safe.

Fix the problem by adding a helper bfq_waker_bfqq() to check if bfqq->waker_bfqq is in the merge chain, and current procress is the only holder.

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/0780451f03bf518bc032a7c584de8f92e2d39d7f
• https://git.kernel.org/stable/c/0b8bda0ff17156cd3f60944527c9d8c9f99f1583
• https://git.kernel.org/stable/c/1ba0403ac6447f2d63914fb760c44a3b19c44eaf
• https://git.kernel.org/stable/c/63a07379fdb6c72450cb05294461c6016b8b7726
• https://git.kernel.org/stable/c/cae58d19121a70329cf971359e2518c93fec04fe
• https://git.kernel.org/stable/c/de0456460f2abf921e356ed2bd8da87a376680bd