[PATCH] hfs: Fix OOB Read in __hfs_brec_find

[Peng Zhang <zhangpeng362@huawei.com>]

From: ZhangPeng <zhangpeng362@huawei.com>

Syzbot reported a OOB read bug:

==================================================================
BUG: KASAN: slab-out-of-bounds in hfs_strcmp+0x117/0x190
fs/hfs/string.c:84
Read of size 1 at addr ffff88807eb62c4e by task kworker/u4:1/11
CPU: 1 PID: 11 Comm: kworker/u4:1 Not tainted
6.1.0-rc6-syzkaller-00308-g644e9524388a #0
Workqueue: writeback wb_workfn (flush-7:0)
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0x1b1/0x28e lib/dump_stack.c:106
 print_address_description+0x74/0x340 mm/kasan/report.c:284
 print_report+0x107/0x1f0 mm/kasan/report.c:395
 kasan_report+0xcd/0x100 mm/kasan/report.c:495
 hfs_strcmp+0x117/0x190 fs/hfs/string.c:84
 __hfs_brec_find+0x213/0x5c0 fs/hfs/bfind.c:75
 hfs_brec_find+0x276/0x520 fs/hfs/bfind.c:138
 hfs_write_inode+0x34c/0xb40 fs/hfs/inode.c:462
 write_inode fs/fs-writeback.c:1440 [inline]

If the input inode of hfs_write_inode() is incorrect:
struct inode
  struct hfs_inode_info
    struct hfs_cat_key
      struct hfs_name
        u8 len # len is greater than HFS_NAMELEN(31) which is the
maximum length of an HFS filename

OOB read occurred:
hfs_write_inode()
  hfs_brec_find()
    __hfs_brec_find()
      hfs_cat_keycmp()
        hfs_strcmp() # OOB read occurred due to len is too large

Fix this by adding a Check on len in hfs_write_inode() before calling
hfs_brec_find().

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Reported-by: syzbot+e836ff7133ac02be825f@syzkaller.appspotmail.com
Signed-off-by: ZhangPeng <zhangpeng362@huawei.com>
---
 fs/hfs/inode.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/fs/hfs/inode.c b/fs/hfs/inode.c
index c4526f16355d..a0746be3c1de 100644
--- a/fs/hfs/inode.c
+++ b/fs/hfs/inode.c
@@ -458,6 +458,8 @@ int hfs_write_inode(struct inode *inode, struct writeback_control *wbc)
 		/* panic? */
 		return -EIO;
 
+	if (HFS_I(main_inode)->cat_key.CName.len > HFS_NAMELEN)
+		return -EIO;
 	fd.search_key->cat = HFS_I(main_inode)->cat_key;
 	if (hfs_brec_find(&fd))
 		/* panic? */
-- 
2.25.1