[PATCH 3/3] lockd: Avoid hashing uninitialized bytes in nlm4svc_lookup_file()

[Chuck Lever <cel@kernel.org>]

From: Chuck Lever <chuck.lever@oracle.com>

file_hash() digests the first LOCKD_FH_HASH_SIZE bytes of
nfs_fh.data when bucketing nlm_files[], independent of fh.size.
Commit 3de744ee4e45 ("lockd: Use xdrgen XDR functions for the
NLMv4 TEST procedure") set .pc_argzero to zero for the converted
procedures and moved file-handle population into
nlm4svc_lookup_file(), which copies only xdr_lock->fh.len bytes
into lock->fh.data.

When an NLMv4 client presents a file handle shorter than
LOCKD_FH_HASH_SIZE, bytes fh.len..31 retain whatever the argument
buffer held from an earlier request.  The same wire handle then
hashes to different buckets across calls; nlm_lookup_file() misses
the existing nlm_file entry, and lock-state lookups fail.

Zero only the tail bytes that file_hash() would otherwise consume.
Handles of LOCKD_FH_HASH_SIZE or larger already populate every byte
that file_hash() reads.

Reported-by: Jeff Layton <jlayton@kernel.org>
Closes: https://lore.kernel.org/r/5229a9746d723a3f830120c0b966510f75badfc2.camel@kernel.org
Fixes: 3de744ee4e45 ("lockd: Use xdrgen XDR functions for the NLMv4 TEST procedure")
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
---
 fs/lockd/lockd.h    | 8 ++++++++
 fs/lockd/svc4proc.c | 3 +++
 fs/lockd/svcsubs.c  | 3 +--
 3 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/fs/lockd/lockd.h b/fs/lockd/lockd.h
index 0be0dac59ea2..e418a50c4180 100644
--- a/fs/lockd/lockd.h
+++ b/fs/lockd/lockd.h
@@ -52,6 +52,14 @@
  */
 #define LOCKD_DFLT_TIMEO	10
 
+/*
+ * Number of leading bytes of nfs_fh.data that file_hash()
+ * digests when bucketing nlm_files[]. Sized for historical
+ * NFSv2 handles; nfs_fh.data must be initialized at least
+ * this far before lookup, regardless of fh.size.
+ */
+#define LOCKD_FH_HASH_SIZE	32
+
 /* error codes new to NLMv4 */
 #define	nlm4_deadlock		cpu_to_be32(NLM_DEADLCK)
 #define	nlm4_rofs		cpu_to_be32(NLM_ROFS)
diff --git a/fs/lockd/svc4proc.c b/fs/lockd/svc4proc.c
index 997f4f437997..78e675470c4b 100644
--- a/fs/lockd/svc4proc.c
+++ b/fs/lockd/svc4proc.c
@@ -156,6 +156,9 @@ nlm4svc_lookup_file(struct svc_rqst *rqstp, struct nlm_host *host,
 		return nlm_lck_denied_nolocks;
 	lock->fh.size = xdr_lock->fh.len;
 	memcpy(lock->fh.data, xdr_lock->fh.data, xdr_lock->fh.len);
+	if (xdr_lock->fh.len < LOCKD_FH_HASH_SIZE)
+		memset(lock->fh.data + xdr_lock->fh.len, 0,
+		       LOCKD_FH_HASH_SIZE - xdr_lock->fh.len);
 
 	lock->oh.len = xdr_lock->oh.len;
 	lock->oh.data = xdr_lock->oh.data;
diff --git a/fs/lockd/svcsubs.c b/fs/lockd/svcsubs.c
index 58b87ec52930..a0d1a6fbf61e 100644
--- a/fs/lockd/svcsubs.c
+++ b/fs/lockd/svcsubs.c
@@ -17,7 +17,6 @@
 #include <linux/sunrpc/addr.h>
 #include <linux/module.h>
 #include <linux/mount.h>
-#include <uapi/linux/nfs2.h>
 
 #include "lockd.h"
 #include "share.h"
@@ -67,7 +66,7 @@ static inline unsigned int file_hash(struct nfs_fh *f)
 {
 	unsigned int tmp=0;
 	int i;
-	for (i=0; i<NFS2_FHSIZE;i++)
+	for (i = 0; i < LOCKD_FH_HASH_SIZE; i++)
 		tmp += f->data[i];
 	return tmp & (FILE_NRHASH - 1);
 }
-- 
2.54.0