CVE-2024-26630

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

mm: cachestat: fix folio read-after-free in cache walk

In cachestat, we access the folio from the page caches xarray to compute its page offset, and check for its dirty and writeback flags. However, we do not hold a reference to the folio before performing these actions, which means the folio can concurrently be released and reused as another folio/page/slab.

Get around this altogether by just using xarrays existing machinery for the folio page offsets and dirty/writeback states.

This changes behavior for tmpfs files to now always report zeroes in their dirty and writeback counters. This is okay as tmpfs doesnt follow conventional writeback cache behavior: its pages get cleaned during swapout, after which theyre no longer resident etc.

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/3a75cb05d53f4a6823a32deb078de1366954a804
• https://git.kernel.org/stable/c/ba60fdf75e89ea762bb617be578dc47f27655117
• https://git.kernel.org/stable/c/fe7e008e0ce728252e4ec652cceebcc62211657c
• https://git.kernel.org/stable/c/3a75cb05d53f4a6823a32deb078de1366954a804
• https://git.kernel.org/stable/c/ba60fdf75e89ea762bb617be578dc47f27655117
• https://git.kernel.org/stable/c/fe7e008e0ce728252e4ec652cceebcc62211657c