ksmbd: skip lock-range check on equal size to avoid size==0 underflow

When size equals the current i_size (including 0), the code used to call
check_lock_range(filp, i_size, size - 1, WRITE), which computes `size - 1`
and can underflow for size==0. Skip the equal case.

Cc: stable@vger.kernel.org
Reported-by: Qianchang Zhao <pioooooooooip@gmail.com>
Reported-by: Zhitong Liu <liuzhitong1993@gmail.com>
Signed-off-by: Qianchang Zhao <pioooooooooip@gmail.com>
Acked-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>

diff --git a/fs/smb/server/vfs.c b/fs/smb/server/vfs.c
index 891ed2dc2b7351a5cb14a2241d71095ffdd03f08..90e693e4e41497813133a0c013759696e1b85232 100644 (file)
--- a/fs/smb/server/vfs.c
+++ b/fs/smb/server/vfs.c
@@ -324,6 +324,9 @@ static int check_lock_range(struct file *filp, loff_t start, loff_t end,
        struct file_lock_context *ctx = locks_inode_context(file_inode(filp));
        int error = 0;
 
+       if (start == end)
+               return 0;
+
        if (!ctx || list_empty_careful(&ctx->flc_posix))
                return 0;
 
@@ -828,7 +831,7 @@ int ksmbd_vfs_truncate(struct ksmbd_work *work,
                if (size < inode->i_size) {
                        err = check_lock_range(filp, size,
                                               inode->i_size - 1, WRITE);
-               } else {
+               } else if (size > inode->i_size) {
                        err = check_lock_range(filp, inode->i_size,
                                               size - 1, WRITE);
                }