From 041f57056e5fb9c80adc088269322d2c61074406 Mon Sep 17 00:00:00 2001 From: Jeff Layton Date: Sat, 30 May 2026 09:19:25 -0400 Subject: [PATCH] nfsd: validate symlink target length in NFSv4 CREATE 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: 1da177e4c3f4 ("Linux-2.6.12-rc2") Cc: stable@vger.kernel.org Assisted-by: kres:claude-opus-4-7 Reported-by: Chris Mason Signed-off-by: Jeff Layton Link: https://patch.msgid.link/20260530-nfsd-fixes-v2-9-f27e8eb4d974@kernel.org Signed-off-by: Chuck Lever --- fs/nfsd/nfs4xdr.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/fs/nfsd/nfs4xdr.c b/fs/nfsd/nfs4xdr.c index 09068ca61b00..c37c9722b8c6 100644 --- a/fs/nfsd/nfs4xdr.c +++ b/fs/nfsd/nfs4xdr.c @@ -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;