cifs: don't dereference smb_file_target before null check

There is a null check on dst_file->private data which suggests
it can be potentially null. However, before this check, pointer
smb_file_target is derived from dst_file->private and dereferenced
in the call to tlink_tcon, hence there is a potential null pointer
deference.

Fix this by assigning smb_file_target and target_tcon after the
null pointer sanity checks.

Detected by CoverityScan, CID#1475302 ("Dereference before null check")

Fixes: 04b38d601239 ("vfs: pull btrfs clone API to vfs layer")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Steve French <stfrench@microsoft.com>

diff --git a/fs/cifs/cifsfs.c b/fs/cifs/cifsfs.c
index 1b21262..865706e 100644 (file)
--- a/fs/cifs/cifsfs.c
+++ b/fs/cifs/cifsfs.c
@@ -999,8 +999,8 @@ static loff_t cifs_remap_file_range(struct file *src_file, loff_t off,
        struct inode *src_inode = file_inode(src_file);
        struct inode *target_inode = file_inode(dst_file);
        struct cifsFileInfo *smb_file_src = src_file->private_data;
-       struct cifsFileInfo *smb_file_target = dst_file->private_data;
-       struct cifs_tcon *target_tcon = tlink_tcon(smb_file_target->tlink);
+       struct cifsFileInfo *smb_file_target;
+       struct cifs_tcon *target_tcon;
        unsigned int xid;
        int rc;
 
@@ -1017,6 +1017,9 @@ static loff_t cifs_remap_file_range(struct file *src_file, loff_t off,
                goto out;
        }
 
+       smb_file_target = dst_file->private_data;
+       target_tcon = tlink_tcon(smb_file_target->tlink);
+
        /*
         * Note: cifs case is easier than btrfs since server responsible for
         * checks for proper open modes and file type and if it wants