nfsd: reject out-of-range useconds in NFSv2 SETATTR/CREATE

The NFSv2 sattr decoder converts the wire useconds to nanoseconds in
svcxdr_decode_sattr():

	iap->ia_atime.tv_nsec = tmp2 * NSEC_PER_USEC;

tmp2 is a u32 and NSEC_PER_USEC is 1000, so the product is computed in
unsigned long. On ILP32 that is 32 bits, and an out-of-range useconds
value such as 4294968 wraps to tv_nsec == 704. The corruption therefore
happens during decode, before any proc function can inspect the value,
and a later range check on tv_nsec would see an in-range result and
accept it. Rejecting in the decoder yields an RPC GARBAGE_ARGS reply.
NFSv2 defines no NFSERR_INVAL, so there is no NFS-level status to return
for a malformed time argument, and the check cannot move to the proc
function the way the v3/v4 nsec range checks do.

Guard the raw useconds before the multiplication and reject values
greater than 1000000. useconds == 1000000 is kept: it is the Sun
convention for "set to the current server time", and the in-tree Linux
NFSv2 client emits it in both the atime and the mtime field for a plain
touch / utimes(file, NULL) (see encode_sattr() and
xdr_encode_current_server_time() in fs/nfs/nfs2xdr.c). Rejecting 1000000
would turn that common operation into a hard decode failure for both
SETATTR and CREATE. 1000000 * NSEC_PER_USEC is 10^9, which does not wrap
on ILP32, so the Sun convention value passes through safely. Only
genuinely out-of-range values (> 1000000) are rejected. The atime and
mtime guards are therefore symmetric.

The decoder only applied the Sun convention in the mtime block, which
clears ATTR_ATIME_SET|ATTR_MTIME_SET when mtime useconds == 1000000. If a
client puts 1000000 in the atime field but not in the mtime field, the
atime block stored an out-of-range tv_nsec (10^9) and left ATTR_ATIME_SET
set, so the bogus value reached the filesystem. Apply the convention in
the atime block as well, clearing ATTR_ATIME_SET so the server uses its
current time and ignores the value. Only ATTR_ATIME_SET is cleared there.
The mtime block keeps its existing behavior, where 1000000 means "set
both atime and mtime to now".

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Cc: stable@vger.kernel.org
Signed-off-by: Robbie Ko <robbieko@synology.com>
[ cel: various tweaks, addenda, and clean-ups ]
Link: https://patch.msgid.link/20260616054027.2360930-1-robbieko@synology.com
Signed-off-by: Chuck Lever <cel@kernel.org>

1 files changed, 22 insertions, 10 deletions

diff --git a/fs/nfsd/nfsxdr.c b/fs/nfsd/nfsxdr.c
index ae71e0621317..86c9dd4b334b 100644
--- a/fs/nfsd/nfsxdr.c
+++ b/fs/nfsd/nfsxdr.c
@@ -10,6 +10,16 @@
 #include "auth.h"
 
 /*
+ * Sun convention: a sattr time-useconds field of one full second (an
+ * otherwise out-of-range value) means "set this time to the current
+ * server time." It's needed to make permissions checks for the "touch"
+ * program across NFSv2 mounts work correctly. See description of
+ * sattr in section 6.1 of "NFS Illustrated" by Brent Callaghan,
+ * Addison-Wesley, ISBN 0-201-32750-5
+ */
+#define NFS2_SATTR_SET_TO_SERVER_TIME	(1000000)
+
+/*
  * Mapping of S_IF* types to NFS file types
  */
 static const u32 nfs_ftypes[] = {
@@ -172,27 +182,29 @@ svcxdr_decode_sattr(struct svc_rqst *rqstp, struct xdr_stream *xdr,
 	tmp1 = be32_to_cpup(p++);
 	tmp2 = be32_to_cpup(p++);
 	if (tmp1 != (u32)-1 && tmp2 != (u32)-1) {
+		/*
+		 * Range test here to prevent the multiplication from
+		 * wrapping to a valid (but incorrect) value on 32-bit
+		 * platforms.
+		 */
+		if (tmp2 > NFS2_SATTR_SET_TO_SERVER_TIME)
+			return false;
 		iap->ia_valid |= ATTR_ATIME | ATTR_ATIME_SET;
 		iap->ia_atime.tv_sec = tmp1;
 		iap->ia_atime.tv_nsec = tmp2 * NSEC_PER_USEC;
+		if (tmp2 == NFS2_SATTR_SET_TO_SERVER_TIME)
+			iap->ia_valid &= ~ATTR_ATIME_SET;
 	}
 
 	tmp1 = be32_to_cpup(p++);
 	tmp2 = be32_to_cpup(p++);
 	if (tmp1 != (u32)-1 && tmp2 != (u32)-1) {
+		if (tmp2 > NFS2_SATTR_SET_TO_SERVER_TIME)
+			return false;
 		iap->ia_valid |= ATTR_MTIME | ATTR_MTIME_SET;
 		iap->ia_mtime.tv_sec = tmp1;
 		iap->ia_mtime.tv_nsec = tmp2 * NSEC_PER_USEC;
-		/*
-		 * Passing the invalid value useconds=1000000 for mtime
-		 * is a Sun convention for "set both mtime and atime to
-		 * current server time".  It's needed to make permissions
-		 * checks for the "touch" program across v2 mounts to
-		 * Solaris and Irix boxes work correctly. See description of
-		 * sattr in section 6.1 of "NFS Illustrated" by
-		 * Brent Callaghan, Addison-Wesley, ISBN 0-201-32750-5
-		 */
-		if (tmp2 == 1000000)
+		if (tmp2 == NFS2_SATTR_SET_TO_SERVER_TIME)
 			iap->ia_valid &= ~(ATTR_ATIME_SET|ATTR_MTIME_SET);
 	}