PT-2026-30185 · Linux · Linux
Published
2026-04-03
·
Updated
2026-04-03
·
CVE-2026-31402
None
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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.
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Related Identifiers
Affected Products
Linux