nfsd: fix refcount leak in nfsd_set_fh_dentry()
[ Upstream commit 8a7348a9ed70bda1c1f51d3f1815bcbdf9f3b38c ]
nfsd exports a "pseudo root filesystem" which is used by NFSv4 to find
the various exported filesystems using LOOKUP requests from a known root
filehandle. NFSv3 uses the MOUNT protocol to find those exported
filesystems and so is not given access to the pseudo root filesystem.
If a v3 (or v2) client uses a filehandle from that filesystem,
nfsd_set_fh_dentry() will report an error, but still stores the export
in "struct svc_fh" even though it also drops the reference (exp_put()).
This means that when fh_put() is called an extra reference will be dropped
which can lead to use-after-free and possible denial of service.
Normal NFS usage will not provide a pseudo-root filehandle to a v3
client. This bug can only be triggered by the client synthesising an
incorrect filehandle.
To fix this we move the assignments to the svc_fh later, after all
possible error cases have been detected.
BUG=b/463623427
TEST=presubmit
RELEASE_NOTE=Fixed CVE-2025-40212 in the Linux kernel.
cos-patch: security-high
Reported-and-tested-by: tianshuo han <hantianshuo233@gmail.com>
Fixes: ef7f6c4904d0 ("nfsd: move V4ROOT version check to nfsd_set_fh_dentry()")
Signed-off-by: NeilBrown <neil@brown.name>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Cc: stable@vger.kernel.org
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Change-Id: Ic6bf40780bc7dc5a79b63aaf23afbb4aa51893d1
Reviewed-on: https://cos-review.googlesource.com/c/third_party/kernel/+/119546
Main-Branch-Verified: Cusky Presubmit Bot <presubmit@cos-infra-prod.iam.gserviceaccount.com>
Tested-by: Cusky Presubmit Bot <presubmit@cos-infra-prod.iam.gserviceaccount.com>
Reviewed-by: Miri Amarilio <mirilio@google.com>
Reviewed-on: https://cos-review.googlesource.com/c/third_party/kernel/+/119621
diff --git a/fs/nfsd/nfsfh.c b/fs/nfsd/nfsfh.c
index 854dcdc..9e85fdc 100644
--- a/fs/nfsd/nfsfh.c
+++ b/fs/nfsd/nfsfh.c
@@ -268,9 +268,6 @@ static __be32 nfsd_set_fh_dentry(struct svc_rqst *rqstp, struct net *net,
dentry);
}
- fhp->fh_dentry = dentry;
- fhp->fh_export = exp;
-
switch (fhp->fh_maxsize) {
case NFS4_FHSIZE:
if (dentry->d_sb->s_export_op->flags & EXPORT_OP_NOATOMIC_ATTR)
@@ -292,6 +289,9 @@ static __be32 nfsd_set_fh_dentry(struct svc_rqst *rqstp, struct net *net,
goto out;
}
+ fhp->fh_dentry = dentry;
+ fhp->fh_export = exp;
+
return 0;
out:
exp_put(exp);
