Kernel will iterates over ATTR_RECORDs in mft record in ntfs_attr_find().
To ensure access on these ATTR_RECORDs are within bounds, kernel will
do some checking during iteration.
The problem is that during checking whether ATTR_RECORD's name is within
bounds, kernel will dereferences the ATTR_RECORD name_offset field,
before checking this ATTR_RECORD strcture is within bounds. This problem
may result out-of-bounds read in ntfs_attr_find(), reported by
Syzkaller:
==================================================================
BUG: KASAN: use-after-free in ntfs_attr_find+0xc02/0xce0 fs/ntfs/attrib.c:597
Read of size 2 at addr ffff88807e352009 by task syz-executor153/3607
[...]
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
ntfs_attr_find+0xc02/0xce0 fs/ntfs/attrib.c:597
ntfs_attr_lookup+0x1056/0x2070 fs/ntfs/attrib.c:1193
ntfs_read_inode_mount+0x89a/0x2580 fs/ntfs/inode.c:1845
ntfs_fill_super+0x1799/0x9320 fs/ntfs/super.c:2854
mount_bdev+0x34d/0x410 fs/super.c:1400
legacy_get_tree+0x105/0x220 fs/fs_context.c:610
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:ffffea0001f8d400 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x7e350
head:ffffea0001f8d400 order:3 compound_mapcount:0 compound_pincount:0
flags: 0xfff00000010200(slab|head|node=0|zone=1|lastcpupid=0x7ff)
raw: 00fff00000010200 0000000000000000 dead000000000122 ffff888011842140
raw: 0000000000000000 0000000000040004 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected
Memory state around the buggy address:
ffff88807e351f00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff88807e351f80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff88807e352000: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff88807e352080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff88807e352100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================
This patch solves it by moving the ATTR_RECORD strcture's bounds
checking earlier, then checking whether ATTR_RECORD's name
is within bounds. What's more, this patch also add some comments
to improve its maintainability.
Reported-and-tested-by: [email protected]
Signed-off-by: chenxiaosong (A) <[email protected]>
Link: https://lore.kernel.org/all/[email protected]/
Signed-off-by: Dan Carpenter <[email protected]>
Link: https://groups.google.com/g/syzkaller-bugs/c/t_XdeKPGTR4/m/LECAuIGcBgAJ
Signed-off-by: Hawkins Jiawei <[email protected]>
---
v1->v2:
* Refactor check on Attribute Record Header
suggested by Dan Carpenter.
fs/ntfs/attrib.c | 20 ++++++++++++++++----
1 file changed, 16 insertions(+), 4 deletions(-)
diff --git a/fs/ntfs/attrib.c b/fs/ntfs/attrib.c
index 52615e6090e1..cec4be2a2d23 100644
--- a/fs/ntfs/attrib.c
+++ b/fs/ntfs/attrib.c
@@ -594,11 +594,23 @@ static int ntfs_attr_find(const ATTR_TYPE type, const ntfschar *name,
for (;; a = (ATTR_RECORD*)((u8*)a + le32_to_cpu(a->length))) {
u8 *mrec_end = (u8 *)ctx->mrec +
le32_to_cpu(ctx->mrec->bytes_allocated);
- u8 *name_end = (u8 *)a + le16_to_cpu(a->name_offset) +
- a->name_length * sizeof(ntfschar);
- if ((u8*)a < (u8*)ctx->mrec || (u8*)a > mrec_end ||
- name_end > mrec_end)
+ u8 *name_end;
+
+ /* check whether ATTR_RECORD wrap */
+ if ((u8 *)a < (u8 *)ctx->mrec)
+ break;
+
+ /* check whether Attribute Record Header is within bounds */
+ if ((u8 *)a > mrec_end ||
+ (u8 *)a + sizeof(ATTR_RECORD) > mrec_end)
break;
+
+ /* check whether ATTR_RECORD's name is within bounds */
+ name_end = (u8 *)a + le16_to_cpu(a->name_offset) +
+ a->name_length * sizeof(ntfschar);
+ if (name_end > mrec_end)
+ break;
+
ctx->attr = a;
if (unlikely(le32_to_cpu(a->type) > le32_to_cpu(type) ||
a->type == AT_END))
--
2.25.1