[PATCH] fs: reiserfs: fix NULL pointer dereference in

[tcs.kernel@gmail.com]

From: Haimin Zhang <tcs_kernel@tencent.com> 

If root_inode->i_op is reiserfs_special_inode_operations
reiserfs_special_inode_operations doesn't implement the lookup callback
function,resulting an NULL pointer when the reiserfs_lookup_privroot() 
function was called.

Call Trace:
 __lookup_slow+0x267/0x490 build/../fs/namei.c:1646
 lookup_one_len+0x163/0x190 build/../fs/namei.c:2663
 reiserfs_lookup_privroot+0x92/0x290 build/../fs/reiserfs/xattr.c:980
 reiserfs_fill_super+0x1f2a/0x2d80 build/../fs/reiserfs/super.c:2176
 mount_bdev+0x33d/0x410 build/../fs/super.c:1368
 legacy_get_tree+0x103/0x210 build/../fs/fs_context.c:610
 vfs_get_tree+0x86/0x2f0 build/../fs/super.c:1498
 do_new_mount build/../fs/namespace.c:2905 [inline]
 path_mount+0x688/0x1d10 build/../fs/namespace.c:3235
 do_mount+0xf1/0x110 build/../fs/namespace.c:3248
 __do_sys_mount build/../fs/namespace.c:3456 [inline]
 __se_sys_mount build/../fs/namespace.c:3433 [inline]
 __x64_sys_mount+0x1d5/0x220 build/../fs/namespace.c:3433
 do_syscall_x64 build/../arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x34/0xb0 build/../arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae

Reported-by: syzbot+11c49c...@syzkaller.appspotmail.com
Signed-off-by: Haimin Zhang <tcs_kernel@tencent.com>
---
 fs/reiserfs/namei.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/fs/reiserfs/namei.c b/fs/reiserfs/namei.c
index 3d7a35d..947b51b 100644
--- a/fs/reiserfs/namei.c
+++ b/fs/reiserfs/namei.c
@@ -350,6 +350,12 @@ static int reiserfs_find_entry(struct inode *dir, const char *name, int namelen,
 	}			/* while (1) */
 }
 
+static struct dentry *reiserfs_noop_lookup(struct inode *dir, struct dentry *dentry,
+				      unsigned int flags)
+{
+	return ERR_PTR(-ENOENT);
+}
+
 static struct dentry *reiserfs_lookup(struct inode *dir, struct dentry *dentry,
 				      unsigned int flags)
 {
@@ -1680,6 +1686,7 @@ static int reiserfs_rename(struct user_namespace *mnt_userns,
  * special file operations.. just xattr/acl stuff
  */
 const struct inode_operations reiserfs_special_inode_operations = {
+	.lookup = reiserfs_noop_lookup,
 	.setattr = reiserfs_setattr,
 	.listxattr = reiserfs_listxattr,
 	.permission = reiserfs_permission,
-- 
1.8.3.1