[PATCH v2] ntfs: fix use-after-free in ntfs_ucsncmp()

[PATCH v2] ntfs: fix use-after-free in ntfs_ucsncmp()

[ChenXiaoSong]

Syzkaller reported use-after-free bug as follows:

==================================================================
BUG: KASAN: use-after-free in ntfs_ucsncmp+0x123/0x130
Read of size 2 at addr ffff8880751acee8 by task a.out/879

CPU: 7 PID: 879 Comm: a.out Not tainted 5.19.0-rc4-next-20220630-00001-gcc5218c8bd2c-dirty #7
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.0-0-gd239552ce722-prebuilt.qemu.org 04/01/2014
Call Trace:
 <TASK>
 dump_stack_lvl+0x1c0/0x2b0
 print_address_description.constprop.0.cold+0xd4/0x484
 print_report.cold+0x55/0x232
 kasan_report+0xbf/0xf0
 ntfs_ucsncmp+0x123/0x130
 ntfs_are_names_equal.cold+0x2b/0x41
 ntfs_attr_find+0x43b/0xb90
 ntfs_attr_lookup+0x16d/0x1e0
 ntfs_read_locked_attr_inode+0x4aa/0x2360
 ntfs_attr_iget+0x1af/0x220
 ntfs_read_locked_inode+0x246c/0x5120
 ntfs_iget+0x132/0x180
 load_system_files+0x1cc6/0x3480
 ntfs_fill_super+0xa66/0x1cf0
 mount_bdev+0x38d/0x460
 legacy_get_tree+0x10d/0x220
 vfs_get_tree+0x93/0x300
 do_new_mount+0x2da/0x6d0
 path_mount+0x496/0x19d0
 __x64_sys_mount+0x284/0x300
 do_syscall_64+0x3b/0xc0
 entry_SYSCALL_64_after_hwframe+0x46/0xb0
RIP: 0033:0x7f3f2118d9ea
Code: 48 8b 0d a9 f4 0b 00 f7 d8 64 89 01 48 83 c8 ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 49 89 ca b8 a5 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d 76 f4 0b 00 f7 d8 64 89 01 48
RSP: 002b:00007ffc269deac8 EFLAGS: 00000202 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f3f2118d9ea
RDX: 0000000020000000 RSI: 0000000020000100 RDI: 00007ffc269dec00
RBP: 00007ffc269dec80 R08: 00007ffc269deb00 R09: 00007ffc269dec44
R10: 0000000000000000 R11: 0000000000000202 R12: 000055f81ab1d220
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
 </TASK>

The buggy address belongs to the physical page:
page:0000000085430378 refcount:1 mapcount:1 mapping:0000000000000000 index:0x555c6a81d pfn:0x751ac
memcg:ffff888101f7e180
anon flags: 0xfffffc00a0014(uptodate|lru|mappedtodisk|swapbacked|node=0|zone=1|lastcpupid=0x1fffff)
raw: 000fffffc00a0014 ffffea0001bf2988 ffffea0001de2448 ffff88801712e201
raw: 0000000555c6a81d 0000000000000000 0000000100000000 ffff888101f7e180
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8880751acd80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 ffff8880751ace00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>ffff8880751ace80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
                                                          ^
 ffff8880751acf00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 ffff8880751acf80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
==================================================================

The reason is that struct ATTR_RECORD->name_offset is 6485, end address of
name string is out of bounds.

Fix this by adding sanity check on end address of attibute name string.

Signed-off-by: ChenXiaoSong <chenxiaosong2@huawei.com>
---
v1 -> v2: remove redundant statement

 fs/ntfs/attrib.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/fs/ntfs/attrib.c b/fs/ntfs/attrib.c
index 4de597a83b88..9ab8766872d2 100644
--- a/fs/ntfs/attrib.c
+++ b/fs/ntfs/attrib.c
@@ -592,8 +592,12 @@ static int ntfs_attr_find(const ATTR_TYPE type, const ntfschar *name,
 		a = (ATTR_RECORD*)((u8*)ctx->attr +
 				le32_to_cpu(ctx->attr->length));
 	for (;;	a = (ATTR_RECORD*)((u8*)a + le32_to_cpu(a->length))) {
-		if ((u8*)a < (u8*)ctx->mrec || (u8*)a > (u8*)ctx->mrec +
-				le32_to_cpu(ctx->mrec->bytes_allocated))
+		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;
+		if ((u8*)a < (u8*)ctx->mrec || (u8*)a > mrec_end ||
+		    name_end > mrec_end)
 			break;
 		ctx->attr = a;
 		if (unlikely(le32_to_cpu(a->type) > le32_to_cpu(type) ||
-- 
2.31.1

Re: [PATCH v2] ntfs: fix use-after-free in ntfs_ucsncmp()

[Hawkins Jiawei]

> Fix this by adding sanity check on end address of attibute name string.

> diff --git a/fs/ntfs/attrib.c b/fs/ntfs/attrib.c
> index 4de597a83b88..9ab8766872d2 100644
> --- a/fs/ntfs/attrib.c
> +++ b/fs/ntfs/attrib.c
> @@ -592,8 +592,12 @@ static int ntfs_attr_find(const ATTR_TYPE type, const ntfschar *name,
>  		a = (ATTR_RECORD*)((u8*)ctx->attr +
>  				le32_to_cpu(ctx->attr->length));
>  	for (;;	a = (ATTR_RECORD*)((u8*)a + le32_to_cpu(a->length))) {
> -		if ((u8*)a < (u8*)ctx->mrec || (u8*)a > (u8*)ctx->mrec +
> -				le32_to_cpu(ctx->mrec->bytes_allocated))
> +		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;

In my opinion, name_length field just means the number of characters,
yet each character is a ntfschar type. So name should be
name_length * sizeof(ntfschar) bytes. The example is at
https://elixir.bootlin.com/linux/v5.19-rc5/source/fs/ntfs/attrib.c#L1667

> +		if ((u8*)a < (u8*)ctx->mrec || (u8*)a > mrec_end ||
> +		    name_end > mrec_end)
>  			break;
>  		ctx->attr = a;
>  		if (unlikely(le32_to_cpu(a->type) > le32_to_cpu(type) ||
> -- 

Re: [PATCH v2] ntfs: fix use-after-free in ntfs_ucsncmp()

[chenxiaosong (A)]

在 2022/7/9 8:54, Hawkins Jiawei 写道:> In my opinion, name_length field 
just means the number of characters,
> yet each character is a ntfschar type. So name should be
> name_length * sizeof(ntfschar) bytes. The example is at
> https://elixir.bootlin.com/linux/v5.19-rc5/source/fs/ntfs/attrib.c#L1667

Yes, thank you for your reply, I will send v3 patch.