CVE-2024-35852

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

mlxsw: spectrum_acl_tcam: Fix memory leak when canceling rehash work

The rehash delayed work is rescheduled with a delay if the number of credits at end of the work is not negative as supposedly it means that the migration ended. Otherwise, it is rescheduled immediately.

After mlxsw: spectrum_acl_tcam: Fix possible use-after-free during rehash the above is no longer accurate as a non-negative number of credits is no longer indicative of the migration being done. It can also happen if the work encountered an error in which case the migration will resume the next time the work is scheduled.

The significance of the above is that it is possible for the work to be pending and associated with hints that were allocated when the migration started. This leads to the hints being leaked [1] when the work is canceled while pending as part of ACL region dismantle.

Fix by freeing the hints if hints are associated with a work that was canceled while pending.

Blame the original commit since the reliance on not having a pending work associated with hints is fragile.

[1] unreferenced object 0xffff88810e7c3000 (size 256): comm kworker/0:16, pid 176, jiffies 4295460353 hex dump (first 32 bytes): 00 30 95 11 81 88 ff ff 61 00 00 00 00 00 00 80 .0……a……. 00 00 61 00 40 00 00 00 00 00 00 00 04 00 00 00 ..a.@……….. backtrace (crc 2544ddb9): [<00000000cf8cfab3>] kmalloc_trace+0x23f/0x2a0 [<000000004d9a1ad9>] objagg_hints_get+0x42/0x390 [<000000000b143cf3>] mlxsw_sp_acl_erp_rehash_hints_get+0xca/0x400 [<0000000059bdb60a>] mlxsw_sp_acl_tcam_vregion_rehash_work+0x868/0x1160 [<00000000e81fd734>] process_one_work+0x59c/0xf20 [<00000000ceee9e81>] worker_thread+0x799/0x12c0 [<00000000bda6fe39>] kthread+0x246/0x300 [<0000000070056d23>] ret_from_fork+0x34/0x70 [<00000000dea2b93e>] ret_from_fork_asm+0x1a/0x30

Weakness

The product does not sufficiently track and release allocated memory after it has been used, making the memory unavailable for reallocation and reuse.

Affected Software

Potential Mitigations

• Choose a language or tool that provides automatic memory management, or makes manual memory management less error-prone.
• For example, glibc in Linux provides protection against free of invalid pointers.
• When using Xcode to target OS X or iOS, enable automatic reference counting (ARC) [REF-391].
• To help correctly and consistently manage memory when programming in C++, consider using a smart pointer class such as std::auto_ptr (defined by ISO/IEC ISO/IEC 14882:2003), std::shared_ptr and std::unique_ptr (specified by an upcoming revision of the C++ standard, informally referred to as C++ 1x), or equivalent solutions such as Boost.

References

• https://git.kernel.org/stable/c/51cefc9da400b953fee749c9e5d26cd4a2b5d758
• https://git.kernel.org/stable/c/5bfe7bf9656ed2633718388f12b7c38b86414a04
• https://git.kernel.org/stable/c/63d814d93c5cce4c18284adc810028f28dca493f
• https://git.kernel.org/stable/c/857ed800133ffcfcee28582090b63b0cbb8ba59d
• https://git.kernel.org/stable/c/d72dd6fcd7886d0523afbab8b4a4b22d17addd7d
• https://git.kernel.org/stable/c/de1aaefa75be9d0ec19c9a3e0e2f9696de20c6ab
• https://git.kernel.org/stable/c/fb4e2b70a7194b209fc7320bbf33b375f7114bd5
• https://git.kernel.org/stable/c/51cefc9da400b953fee749c9e5d26cd4a2b5d758
• https://git.kernel.org/stable/c/5bfe7bf9656ed2633718388f12b7c38b86414a04
• https://git.kernel.org/stable/c/63d814d93c5cce4c18284adc810028f28dca493f
• https://git.kernel.org/stable/c/857ed800133ffcfcee28582090b63b0cbb8ba59d
• https://git.kernel.org/stable/c/d72dd6fcd7886d0523afbab8b4a4b22d17addd7d
• https://git.kernel.org/stable/c/de1aaefa75be9d0ec19c9a3e0e2f9696de20c6ab
• https://git.kernel.org/stable/c/fb4e2b70a7194b209fc7320bbf33b375f7114bd5
• https://lists.debian.org/debian-lts-announce/2024/06/msg00017.html