CVE-2026-31402

Summary

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

nfsd: fix heap overflow in NFSv4.0 LOCK replay cache

The NFSv4.0 replay cache uses a fixed 112-byte inline buffer (rp_ibuf[NFSD4_REPLAY_ISIZE]) to store encoded operation responses. This size was calculated based on OPEN responses and does not account for LOCK denied responses, which include the conflicting lock owner as a variable-length field up to 1024 bytes (NFS4_OPAQUE_LIMIT).

When a LOCK operation is denied due to a conflict with an existing lock that has a large owner, nfsd4_encode_operation() copies the full encoded response into the undersized replay buffer via read_bytes_from_xdr_buf() with no bounds check. This results in a slab-out-of-bounds write of up to 944 bytes past the end of the buffer, corrupting adjacent heap memory.

This can be triggered remotely by an unauthenticated attacker with two cooperating NFSv4.0 clients: one sets a lock with a large owner string, then the other requests a conflicting lock to provoke the denial.

We could fix this by increasing NFSD4_REPLAY_ISIZE to allow for a full opaque, but that would increase the size of every stateowner, when most lockowners are not that large.

Instead, fix this by checking the encoded response length against NFSD4_REPLAY_ISIZE before copying into the replay buffer. If the response is too large, set rp_buflen to 0 to skip caching the replay payload. The status is still cached, and the client already received the correct response on the original request.

Affected Software

VendorProductVersion RangeStatus
LinuxLinux1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < f9fcb4441f6c02bb20c2eb340101e27dfe23607caffected
LinuxLinux1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < 2665887a69437a8a4f552f69509eecfb73d4aa19affected
LinuxLinux1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < c9452c0797c95cf2378170df96cf4f4b3bca7effaffected
LinuxLinux1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < 8afb437ea1f70cacb4bbdf11771fb5c4d720b965affected
LinuxLinux1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < dad0c3c0a8e5d1d6eb0fc455694ce3e25e6c57d0affected
LinuxLinux1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < 0f0e2a54a31a7f9ad2915db99156114872317388affected
LinuxLinux1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < ae8498337dfdfda71bdd0b807c9a23a126011d76affected
LinuxLinux1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < 5133b61aaf437e5f25b1b396b14242a6bb0508e2affected
LinuxLinux2.6.12affected
LinuxLinux0 < 2.6.12unaffected
LinuxLinux5.10.253 <= 5.10.*unaffected
LinuxLinux5.15.210 <= 5.15.*unaffected
LinuxLinux6.1.167 <= 6.1.*unaffected
LinuxLinux6.6.130 <= 6.6.*unaffected
LinuxLinux6.12.78 <= 6.12.*unaffected
LinuxLinux6.18.20 <= 6.18.*unaffected
LinuxLinux6.19.10 <= 6.19.*unaffected
LinuxLinux7.0 <= *unaffected

Weaknesses

ADP Enrichment

kernel: nfsd: fix heap overflow in NFSv4.0 LOCK replay cache

Additional References

References