CVE-2026-53250

Summary

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

xsk: cache csum_start/csum_offset to fix TOCTOU in xsk_skb_metadata()

The TX metadata area resides in the UMEM buffer which is memory-mapped and concurrently writable by userspace. In xsk_skb_metadata(), csum_start and csum_offset are read from shared memory for bounds validation, then read again for skb assignment. A malicious userspace application can race to overwrite these values between the two reads, bypassing the bounds check and causing out-of-bounds memory access during checksum computation in the transmit path.

Fix this by reading csum_start and csum_offset into local variables once, then using the local copies for both validation and assignment.

Note that other metadata fields (flags, launch_time) and the cached csum fields may be mutually inconsistent due to concurrent userspace writes, but this is benign: the only security-critical invariant is that each field's validated value is the same one used, which local caching guarantees.

Affected Software

Weaknesses

References

• https://git.kernel.org/stable/c/0dfe05b938435892875e07771170051346412df9
• https://git.kernel.org/stable/c/bfdfd2706d5fb2cd496a1506e680daf979309c8b
• https://git.kernel.org/stable/c/22ba97ea9cc1f63a0d0244fae38057ed452b6ac7

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