fs/ntfs3: Fix null-ptr-deref on inode->i_op in ntfs_lookup()

Syzbot reported a null-ptr-deref bug:

ntfs3: loop0: Different NTFS' sector size (1024) and media sector size
(512)
ntfs3: loop0: Mark volume as dirty due to NTFS errors
general protection fault, probably for non-canonical address
0xdffffc0000000001: 0000 [#1] PREEMPT SMP KASAN
KASAN: null-ptr-deref in range [0x0000000000000008-0x000000000000000f]
RIP: 0010:d_flags_for_inode fs/dcache.c:1980 [inline]
RIP: 0010:__d_add+0x5ce/0x800 fs/dcache.c:2796
Call Trace:
 <TASK>
 d_splice_alias+0x122/0x3b0 fs/dcache.c:3191
 lookup_open fs/namei.c:3391 [inline]
 open_last_lookups fs/namei.c:3481 [inline]
 path_openat+0x10e6/0x2df0 fs/namei.c:3688
 do_filp_open+0x264/0x4f0 fs/namei.c:3718
 do_sys_openat2+0x124/0x4e0 fs/open.c:1310
 do_sys_open fs/open.c:1326 [inline]
 __do_sys_open fs/open.c:1334 [inline]
 __se_sys_open fs/open.c:1330 [inline]
 __x64_sys_open+0x221/0x270 fs/open.c:1330
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x3d/0xb0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd

If the MFT record of ntfs inode is not a base record, inode->i_op can be
NULL. And a null-ptr-deref may happen:

ntfs_lookup()
    dir_search_u() # inode->i_op is set to NULL
    d_splice_alias()
        __d_add()
            d_flags_for_inode() # inode->i_op->get_link null-ptr-deref

Fix this by adding a Check on inode->i_op before calling the
d_splice_alias() function.

Fixes: 4342306f0f0d ("fs/ntfs3: Add file operations and implementation")
Reported-by: syzbot+a8f26a403c169b7593fe@syzkaller.appspotmail.com
Signed-off-by: ZhangPeng <zhangpeng362@huawei.com>
Signed-off-by: Konstantin Komarov <almaz.alexandrovich@paragon-software.com>

diff --git a/fs/ntfs3/namei.c b/fs/ntfs3/namei.c
index 407fe92394e225cf2519e8a2e3658ff6e693e2b1..8d206770d8c6d586ddb7a881572d822aeb2c0467 100644 (file)
--- a/fs/ntfs3/namei.c
+++ b/fs/ntfs3/namei.c
@@ -88,6 +88,16 @@ static struct dentry *ntfs_lookup(struct inode *dir, struct dentry *dentry,
                __putname(uni);
        }
 
+       /*
+        * Check for a null pointer
+        * If the MFT record of ntfs inode is not a base record, inode->i_op can be NULL.
+        * This causes null pointer dereference in d_splice_alias().
+        */
+       if (!IS_ERR(inode) && inode->i_op == NULL) {
+               iput(inode);
+               inode = ERR_PTR(-EINVAL);
+       }
+
        return d_splice_alias(inode, dentry);
 }