[PATCH v2] fs/ntfs3: fix slab-out-of-bounds Read in run_unpack

[Hawkins Jiawei <yin31149@gmail.com>]

Syzkaller reports slab-out-of-bounds bug as follows:
==================================================================
BUG: KASAN: slab-out-of-bounds in run_unpack+0x8b7/0x970 fs/ntfs3/run.c:944
Read of size 1 at addr ffff88801bbdff02 by task syz-executor131/3611

[...]
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0xcd/0x134 lib/dump_stack.c:106
 print_address_description mm/kasan/report.c:317 [inline]
 print_report.cold+0x2ba/0x719 mm/kasan/report.c:433
 kasan_report+0xb1/0x1e0 mm/kasan/report.c:495
 run_unpack+0x8b7/0x970 fs/ntfs3/run.c:944
 run_unpack_ex+0xb0/0x7c0 fs/ntfs3/run.c:1057
 ntfs_read_mft fs/ntfs3/inode.c:368 [inline]
 ntfs_iget5+0xc20/0x3280 fs/ntfs3/inode.c:501
 ntfs_loadlog_and_replay+0x124/0x5d0 fs/ntfs3/fsntfs.c:272
 ntfs_fill_super+0x1eff/0x37f0 fs/ntfs3/super.c:1018
 get_tree_bdev+0x440/0x760 fs/super.c:1323
 vfs_get_tree+0x89/0x2f0 fs/super.c:1530
 do_new_mount fs/namespace.c:3040 [inline]
 path_mount+0x1326/0x1e20 fs/namespace.c:3370
 do_mount fs/namespace.c:3383 [inline]
 __do_sys_mount fs/namespace.c:3591 [inline]
 __se_sys_mount fs/namespace.c:3568 [inline]
 __x64_sys_mount+0x27f/0x300 fs/namespace.c:3568
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd
 [...]
 </TASK>

The buggy address belongs to the physical page:
page:ffffea00006ef600 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x1bbd8
head:ffffea00006ef600 order:3 compound_mapcount:0 compound_pincount:0
flags: 0xfff00000010200(slab|head|node=0|zone=1|lastcpupid=0x7ff)
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff88801bbdfe00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff88801bbdfe80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff88801bbdff00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
                   ^
 ffff88801bbdff80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff88801bbe0000: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================

Kernel will tries to read record and parse MFT from disk in
ntfs_read_mft().

Yet the problem is that during enumerating attributes in record,
kernel doesn't check whether run_off field loading from the disk
is a valid value.

To be more specific, if attr->nres.run_off is larger than attr->size,
kernel will passes an invalid argument run_buf_size in
run_unpack_ex(), which having an integer overflow. Then this invalid
argument will triggers the slab-out-of-bounds Read bug as above.

This patch solves it by adding the sanity check between
the offset to packed runs and attribute size.

link: https://lore.kernel.org/all/0000000000009145fc05e94bd5c3@google.com/#t
Reported-and-tested-by: syzbot+8d6fbb27a6aded64b25b@syzkaller.appspotmail.com
Signed-off-by: Hawkins Jiawei <yin31149@gmail.com>
---
v1 -> v2:
  return -EINVAL when roff is out-of-bounds

 fs/ntfs3/inode.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/fs/ntfs3/inode.c b/fs/ntfs3/inode.c
index 51363d4e8636..10723231e482 100644
--- a/fs/ntfs3/inode.c
+++ b/fs/ntfs3/inode.c
@@ -365,6 +365,13 @@ static struct inode *ntfs_read_mft(struct inode *inode,
 	roff = le16_to_cpu(attr->nres.run_off);
 
 	t64 = le64_to_cpu(attr->nres.svcn);
+
+	/* offset to packed runs is out-of-bounds */
+	if (roff > asize) {
+		err = -EINVAL;
+		goto out;
+	}
+
 	err = run_unpack_ex(run, sbi, ino, t64, le64_to_cpu(attr->nres.evcn),
 			    t64, Add2Ptr(attr, roff), asize - roff);
 	if (err < 0)
-- 
2.25.1