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Subject[PATCH] reiserfs: add check for root_inode in reiserfs_fill_super
Date
Our syzcaller report a NULL pointer dereference:

BUG: kernel NULL pointer dereference, address: 0000000000000000
PGD 116e95067 P4D 116e95067 PUD 1080b5067 PMD 0
Oops: 0010 [#1] SMP KASAN
CPU: 7 PID: 592 Comm: a.out Not tainted 5.13.0-next-20210629-dirty #67
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS ?-20190727_073836-buildvm-p4
RIP: 0010:0x0
Code: Unable to access opcode bytes at RIP 0xffffffffffffffd6.
RSP: 0018:ffff888114e779b8 EFLAGS: 00010246
RAX: 0000000000000000 RBX: 1ffff110229cef39 RCX: ffffffffaa67e1aa
RDX: 0000000000000000 RSI: ffff88810a58ee00 RDI: ffff8881233180b0
RBP: ffffffffac38e9c0 R08: ffffffffaa67e17e R09: 0000000000000001
R10: ffffffffb91c5557 R11: fffffbfff7238aaa R12: ffff88810a58ee00
R13: ffff888114e77aa0 R14: 0000000000000000 R15: ffff8881233180b0
FS: 00007f946163c480(0000) GS:ffff88839f1c0000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffffffffffffffd6 CR3: 00000001099c1000 CR4: 00000000000006e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
__lookup_slow+0x116/0x2d0
? page_put_link+0x120/0x120
? __d_lookup+0xfc/0x320
? d_lookup+0x49/0x90
lookup_one_len+0x13c/0x170
? __lookup_slow+0x2d0/0x2d0
? reiserfs_schedule_old_flush+0x31/0x130
reiserfs_lookup_privroot+0x64/0x150
reiserfs_fill_super+0x158c/0x1b90
? finish_unfinished+0xb10/0xb10
? bprintf+0xe0/0xe0
? __mutex_lock_slowpath+0x30/0x30
? __kasan_check_write+0x20/0x30
? up_write+0x51/0xb0
? set_blocksize+0x9f/0x1f0
mount_bdev+0x27c/0x2d0
? finish_unfinished+0xb10/0xb10
? reiserfs_kill_sb+0x120/0x120
get_super_block+0x19/0x30
legacy_get_tree+0x76/0xf0
vfs_get_tree+0x49/0x160
? capable+0x1d/0x30
path_mount+0xacc/0x1380
? putname+0x97/0xd0
? finish_automount+0x450/0x450
? kmem_cache_free+0xf8/0x5a0
? putname+0x97/0xd0
do_mount+0xe2/0x110
? path_mount+0x1380/0x1380
? copy_mount_options+0x69/0x140
__x64_sys_mount+0xf0/0x190
do_syscall_64+0x35/0x80
entry_SYSCALL_64_after_hwframe+0x44/0xae

This is because 'root_inode' is initialized with wrong mode, and
it's i_op is set to 'reiserfs_special_inode_operations'. Thus add
check for 'root_inode' to fix the problem.

Signed-off-by: Yu Kuai <yukuai3@huawei.com>
---
fs/reiserfs/super.c | 8 ++++++++
1 file changed, 8 insertions(+)

diff --git a/fs/reiserfs/super.c b/fs/reiserfs/super.c
index 3ffafc73acf0..bcf5123ed43b 100644
--- a/fs/reiserfs/super.c
+++ b/fs/reiserfs/super.c
@@ -2082,6 +2082,14 @@ static int reiserfs_fill_super(struct super_block *s, void *data, int silent)
unlock_new_inode(root_inode);
}

+ if (!S_ISDIR(root_inode->i_mode) || !root_inode->i_blocks ||
+ !root_inode->i_size) {
+ SWARN(silent, s, "", "corrupt root inode, run fsck");
+ iput(root_inode);
+ errval = -EUCLEAN;
+ goto error;
+ }
+
s->s_root = d_make_root(root_inode);
if (!s->s_root)
goto error;
--
2.31.1
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