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

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Summary

CVECVE-2026-53250
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-06-25 09:16:42 UTC
Updated2026-06-25 09:16:42 UTC
DescriptionIn 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.

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected 48eb03dd26304c24f03bdbb9382e89c8564e71df 0dfe05b938435892875e07771170051346412df9 git Not specified
CNA Linux Linux affected 48eb03dd26304c24f03bdbb9382e89c8564e71df bfdfd2706d5fb2cd496a1506e680daf979309c8b git Not specified
CNA Linux Linux affected 48eb03dd26304c24f03bdbb9382e89c8564e71df 22ba97ea9cc1f63a0d0244fae38057ed452b6ac7 git Not specified
CNA Linux Linux affected 6.8 Not specified
CNA Linux Linux unaffected 6.8 semver Not specified
CNA Linux Linux unaffected 6.18.36 6.18.* semver Not specified
CNA Linux Linux unaffected 7.0.13 7.0.* semver Not specified
CNA Linux Linux unaffected 7.1 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/0dfe05b938435892875e07771170051346412df9 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/22ba97ea9cc1f63a0d0244fae38057ed452b6ac7 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/bfdfd2706d5fb2cd496a1506e680daf979309c8b 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
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