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nfsd: validate symlink target length in NFSv4 CREATE

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nfsd4_decode_create() accepts an unbounded cr_datalen from the wire for
NF4LNK symlink targets, allowing a client to force a kmalloc of up to
the maximum RPC payload size (several MiB) per COMPOUND op that persists
until compound teardown.  The VFS rejects oversized targets with
ENAMETOOLONG, but the allocation has already occurred.

Reject cr_datalen == 0 early with nfserr_inval and cr_datalen greater
than NFS4_MAXPATHLEN (PATH_MAX) with nfserr_nametoolong to bound the
allocation.

Fixes: 1da177e4c3 ("Linux-2.6.12-rc2")
Cc: stable@vger.kernel.org
Assisted-by: kres:claude-opus-4-7
Reported-by: Chris Mason <clm@meta.com>
Signed-off-by: Jeff Layton <jlayton@kernel.org>
Link: https://patch.msgid.link/20260530-nfsd-fixes-v2-9-f27e8eb4d974@kernel.org
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
This commit is contained in:
Jeff Layton 2026-05-30 09:19:25 -04:00 committed by Chuck Lever
parent 4bc1108e87
commit 041f57056e
1 changed files with 4 additions and 0 deletions
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4
fs/nfsd/nfs4xdr.c
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@ -964,6 +964,10 @@ nfsd4_decode_create(struct nfsd4_compoundargs *argp, union nfsd4_op_u *u)
case NF4LNK:
if (xdr_stream_decode_u32(argp->xdr, &create->cr_datalen) < 0)
return nfserr_bad_xdr;
if (create->cr_datalen == 0)
return nfserr_inval;
if (create->cr_datalen > NFS4_MAXPATHLEN)
return nfserr_nametoolong;
p = xdr_inline_decode(argp->xdr, create->cr_datalen);
if (!p)
return nfserr_bad_xdr;