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From: Hawkins J. <yin...@gm...> - 2022-08-31 16:10:24
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Syzkaller reported use-after-free read as follows:
==================================================================
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
==================================================================
Kernel will loads $MFT/$DATA's first mft record in
ntfs_read_inode_mount().
Yet the problem is that after loading, kernel doesn't check whether
attrs_offset field is a valid value.
To be more specific, if attrs_offset field is larger
than bytes_allocated field, then it may trigger the out-of-bounds read
bug(reported as use-after-free bug) in ntfs_attr_find(), when kernel
tries to access the corresponding mft record's attribute.
This patch solves it by adding the sanity check between attrs_offset
field and bytes_allocated field, after loading the first mft record.
Signed-off-by: Hawkins Jiawei <yin...@gm...>
---
v1->v2:
* No change.
fs/ntfs/inode.c | 7 +++++++
1 file changed, 7 insertions(+)
diff --git a/fs/ntfs/inode.c b/fs/ntfs/inode.c
index db0f1995aedd..08c659332e26 100644
--- a/fs/ntfs/inode.c
+++ b/fs/ntfs/inode.c
@@ -1829,6 +1829,13 @@ int ntfs_read_inode_mount(struct inode *vi)
goto err_out;
}
+ /* Sanity check offset to the first attribute */
+ if (le16_to_cpu(m->attrs_offset) >= le32_to_cpu(m->bytes_allocated)) {
+ ntfs_error(sb, "Incorrect mft offset to the first attribute %u in superblock.",
+ le16_to_cpu(m->attrs_offset));
+ goto err_out;
+ }
+
/* Need this to sanity check attribute list references to $MFT. */
vi->i_generation = ni->seq_no = le16_to_cpu(m->sequence_number);
--
2.25.1
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