[PATCH v2] lockd: detect and reject lock arguments that overflow

[Jeff Layton <jlayton@kernel.org>]

lockd doesn't currently vet the start and length in nlm4 requests like
it should, and can end up generating lock requests with arguments that
overflow when passed to the filesystem.

The NLM4 protocol uses unsigned 64-bit arguments for both start and
length, whereas struct file_lock tracks the start and end as loff_t
values. By the time we get around to calling nlm4svc_retrieve_args,
we've lost the information that would allow us to determine if there was
an overflow.

Start tracking the actual start and len for NLM4 requests in the
nlm_lock. In nlm4svc_retrieve_args, vet these values to ensure they
won't cause an overflow, and return NLM4_FBIG if they do.

Link: https://bugzilla.linux-nfs.org/show_bug.cgi?id=392
Reported-by: Jan Kasiak <j.kasiak@gmail.com>
Signed-off-by: Jeff Layton <jlayton@kernel.org>
---
 fs/lockd/svc4proc.c       |  8 ++++++++
 fs/lockd/xdr4.c           | 19 ++-----------------
 include/linux/lockd/xdr.h |  2 ++
 3 files changed, 12 insertions(+), 17 deletions(-)

v2: record args as u64s in nlm_lock and check them in
    nlm4svc_retrieve_args

diff --git a/fs/lockd/svc4proc.c b/fs/lockd/svc4proc.c
index 176b468a61c7..e5adb524a445 100644
--- a/fs/lockd/svc4proc.c
+++ b/fs/lockd/svc4proc.c
@@ -32,6 +32,10 @@ nlm4svc_retrieve_args(struct svc_rqst *rqstp, struct nlm_args *argp,
 	if (!nlmsvc_ops)
 		return nlm_lck_denied_nolocks;
 
+	if (lock->lock_start > OFFSET_MAX ||
+	    (lock->lock_len && ((lock->lock_len - 1) > (OFFSET_MAX - lock->lock_start))))
+		return nlm4_fbig;
+
 	/* Obtain host handle */
 	if (!(host = nlmsvc_lookup_host(rqstp, lock->caller, lock->len))
 	 || (argp->monitor && nsm_monitor(host) < 0))
@@ -50,6 +54,10 @@ nlm4svc_retrieve_args(struct svc_rqst *rqstp, struct nlm_args *argp,
 		/* Set up the missing parts of the file_lock structure */
 		lock->fl.fl_file  = file->f_file[mode];
 		lock->fl.fl_pid = current->tgid;
+		lock->fl.fl_start = (loff_t)lock->lock_start;
+		lock->fl.fl_end = lock->lock_len ?
+				   (loff_t)(lock->lock_start + lock->lock_len - 1) :
+				   OFFSET_MAX;
 		lock->fl.fl_lmops = &nlmsvc_lock_operations;
 		nlmsvc_locks_init_private(&lock->fl, host, (pid_t)lock->svid);
 		if (!lock->fl.fl_owner) {
diff --git a/fs/lockd/xdr4.c b/fs/lockd/xdr4.c
index 856267c0864b..712fdfeb8ef0 100644
--- a/fs/lockd/xdr4.c
+++ b/fs/lockd/xdr4.c
@@ -20,13 +20,6 @@
 
 #include "svcxdr.h"
 
-static inline loff_t
-s64_to_loff_t(__s64 offset)
-{
-	return (loff_t)offset;
-}
-
-
 static inline s64
 loff_t_to_s64(loff_t offset)
 {
@@ -70,8 +63,6 @@ static bool
 svcxdr_decode_lock(struct xdr_stream *xdr, struct nlm_lock *lock)
 {
 	struct file_lock *fl = &lock->fl;
-	u64 len, start;
-	s64 end;
 
 	if (!svcxdr_decode_string(xdr, &lock->caller, &lock->len))
 		return false;
@@ -81,20 +72,14 @@ svcxdr_decode_lock(struct xdr_stream *xdr, struct nlm_lock *lock)
 		return false;
 	if (xdr_stream_decode_u32(xdr, &lock->svid) < 0)
 		return false;
-	if (xdr_stream_decode_u64(xdr, &start) < 0)
+	if (xdr_stream_decode_u64(xdr, &lock->lock_start) < 0)
 		return false;
-	if (xdr_stream_decode_u64(xdr, &len) < 0)
+	if (xdr_stream_decode_u64(xdr, &lock->lock_len) < 0)
 		return false;
 
 	locks_init_lock(fl);
 	fl->fl_flags = FL_POSIX;
 	fl->fl_type  = F_RDLCK;
-	end = start + len - 1;
-	fl->fl_start = s64_to_loff_t(start);
-	if (len == 0 || end < 0)
-		fl->fl_end = OFFSET_MAX;
-	else
-		fl->fl_end = s64_to_loff_t(end);
 
 	return true;
 }
diff --git a/include/linux/lockd/xdr.h b/include/linux/lockd/xdr.h
index 398f70093cd3..67e4a2c5500b 100644
--- a/include/linux/lockd/xdr.h
+++ b/include/linux/lockd/xdr.h
@@ -41,6 +41,8 @@ struct nlm_lock {
 	struct nfs_fh		fh;
 	struct xdr_netobj	oh;
 	u32			svid;
+	u64			lock_start;
+	u64			lock_len;
 	struct file_lock	fl;
 };
 
-- 
2.37.1