[PATCH 6.1 281/312] ksmbd: fix memory leaks and NULL deref in smb2_lock()

Greg Kroah-Hartman
2026-04-08T18:18:58Z

From: Werner Kasselman <werner@verivus.com>

[ Upstream commit 309b44ed684496ed3f9c5715d10b899338623512 ]

smb2_lock() has three error handling issues after list_del() detaches
smb_lock from lock_list at no_check_cl:

1) If vfs_lock_file() returns an unexpected error in the non-UNLOCK
path, goto out leaks smb_lock and its flock because the out:
handler only iterates lock_list and rollback_list, neither of
which contains the detached smb_lock.

2) If vfs_lock_file() returns -ENOENT in the UNLOCK path, goto out
leaks smb_lock and flock for the same reason. The error code
returned to the dispatcher is also stale.

3) In the rollback path, smb_flock_init() can return NULL on
allocation failure. The result is dereferenced unconditionally,
causing a kernel NULL pointer dereference. Add a NULL check to
prevent the crash and clean up the bookkeeping; the VFS lock
itself cannot be rolled back without the allocation and will be
released at file or connection teardown.

Fix cases 1 and 2 by hoisting the locks_free_lock()/kfree() to before
the if(!rc) check in the UNLOCK branch so all exit paths share one
free site, and by freeing smb_lock and flock before goto out in the
non-UNLOCK branch. Propagate the correct error code in both cases.
Fix case 3 by wrapping the VFS unlock in an if(rlock) guard and adding
a NULL check for locks_free_lock(rlock) in the shared cleanup.

Found via call-graph analysis using sqry.

Fixes: e2f34481b24d ("cifsd: add server-side procedures for SMB3")
Cc: stable@vger.kernel.org
Suggested-by: ChenXiaoSong <chenxiaosong@kylinos.cn>
Signed-off-by: Werner Kasselman <werner@verivus.com>
Reviewed-by: ChenXiaoSong <chenxiaosong@kylinos.cn>
Acked-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>
[ adapted rlock->c.flc_type to rlock->fl_type ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
fs/smb/server/smb2pdu.c | 29 +++++++++++++++++++----------
1 file changed, 19 insertions(+), 10 deletions(-)

--- a/fs/smb/server/smb2pdu.c
+++ b/fs/smb/server/smb2pdu.c
@@ -7145,14 +7145,15 @@ retry:
rc = vfs_lock_file(filp, smb_lock->cmd, flock, NULL);
skip:
if (smb_lock->flags & SMB2_LOCKFLAG_UNLOCK) {
+ locks_free_lock(flock);
+ kfree(smb_lock);
if (!rc) {
ksmbd_debug(SMB, "File unlocked\n");
} else if (rc == -ENOENT) {
rsp->hdr.Status = STATUS_NOT_LOCKED;
+ err = rc;
goto out;
}
- locks_free_lock(flock);
- kfree(smb_lock);
} else {
if (rc == FILE_LOCK_DEFERRED) {
void **argv;
@@ -7221,6 +7222,9 @@ skip:
spin_unlock(&work->conn->llist_lock);
ksmbd_debug(SMB, "successful in taking lock\n");
} else {
+ locks_free_lock(flock);
+ kfree(smb_lock);
+ err = rc;
goto out;
}
}
@@ -7251,13 +7255,17 @@ out:
struct file_lock *rlock = NULL;

rlock = smb_flock_init(filp);
- rlock->fl_type = F_UNLCK;
- rlock->fl_start = smb_lock->start;
- rlock->fl_end = smb_lock->end;
-
- rc = vfs_lock_file(filp, F_SETLK, rlock, NULL);
- if (rc)
- pr_err("rollback unlock fail : %d\n", rc);
+ if (rlock) {
+ rlock->fl_type = F_UNLCK;
+ rlock->fl_start = smb_lock->start;
+ rlock->fl_end = smb_lock->end;
+
+ rc = vfs_lock_file(filp, F_SETLK, rlock, NULL);
+ if (rc)
+ pr_err("rollback unlock fail : %d\n", rc);
+ } else {
+ pr_err("rollback unlock alloc failed\n");
+ }

list_del(&smb_lock->llist);
spin_lock(&work->conn->llist_lock);
@@ -7267,7 +7275,8 @@ out:
spin_unlock(&work->conn->llist_lock);

locks_free_lock(smb_lock->fl);
- locks_free_lock(rlock);
+ if (rlock)
+ locks_free_lock(rlock);
kfree(smb_lock);
}
out2: