2020-08-23 15:28:30

by Rustam Kovhaev

Subject: [PATCH] ntfs: add check for mft record size in superblock

number of bytes allocated for mft record should be equal to the mft
record size stored in ntfs superblock
as reported by syzbot, userspace might trigger out-of-bounds read by
dereferencing ctx->attr in ntfs_attr_find()

Reported-and-tested-by: [email protected]
Link: https://syzkaller.appspot.com/bug?extid=aed06913f36eff9b544e
Signed-off-by: Rustam Kovhaev <[email protected]>
---
fs/ntfs/inode.c | 6 ++++++
1 file changed, 6 insertions(+)

diff --git a/fs/ntfs/inode.c b/fs/ntfs/inode.c
index 9bb9f0952b18..6407af7c2e4f 100644
--- a/fs/ntfs/inode.c
+++ b/fs/ntfs/inode.c
@@ -1810,6 +1810,12 @@ int ntfs_read_inode_mount(struct inode *vi)
brelse(bh);
}

+ if (m->bytes_allocated != vol->mft_record_size) {
+ ntfs_error(sb, "Incorrect mft record size [%u] in superblock, should be [%u].",
+ m->bytes_allocated, vol->mft_record_size);
+ goto err_out;
+ }
+
/* Apply the mst fixups. */
if (post_read_mst_fixup((NTFS_RECORD*)m, vol->mft_record_size)) {
/* FIXME: Try to use the $MFTMirr now. */
--
2.28.0

2020-08-24 02:33:40

by Rustam Kovhaev

Subject: Re: [PATCH] ntfs: add check for mft record size in superblock

On Mon, Aug 24, 2020 at 01:44:06AM +0000, Anton Altaparmakov wrote:
> Hi Rustam,
>
> Thank you for the patch but it introduces an endianness bug - you have to us le32_to_cpu(m->bytes_allocated) both when doing the comparison and then printing the message.
>
> Also, please drop the square brackets. Wherever the driver prints such things it never uses brackets around the numbers and it would be better to have this consistent throughout.
>
> Can you please resend with the above issues addressed? You can then also add to the commit message:
>
> Acked-by: Anton Altaparmakov <[email protected]>
>
> Thanks!
>
> Best regards,
>
> Anton
>
hi Anton,
thank you for the review, my bad, i'll get it fixed and i'll resend the patch

2020-08-24 03:15:22

by Anton Altaparmakov

Subject: Re: [PATCH] ntfs: add check for mft record size in superblock

Hi Rustam,

Thank you for the patch but it introduces an endianness bug - you have to us le32_to_cpu(m->bytes_allocated) both when doing the comparison and then printing the message.

Also, please drop the square brackets. Wherever the driver prints such things it never uses brackets around the numbers and it would be better to have this consistent throughout.

Can you please resend with the above issues addressed? You can then also add to the commit message:

Acked-by: Anton Altaparmakov <[email protected]>

Thanks!

Best regards,

Anton

> On 23 Aug 2020, at 16:21, Rustam Kovhaev <[email protected]> wrote:
>
> number of bytes allocated for mft record should be equal to the mft
> record size stored in ntfs superblock
> as reported by syzbot, userspace might trigger out-of-bounds read by
> dereferencing ctx->attr in ntfs_attr_find()
>
> Reported-and-tested-by: [email protected]
> Link: https://syzkaller.appspot.com/bug?extid=aed06913f36eff9b544e
> Signed-off-by: Rustam Kovhaev <[email protected]>
> ---
> fs/ntfs/inode.c | 6 ++++++
> 1 file changed, 6 insertions(+)
>
> diff --git a/fs/ntfs/inode.c b/fs/ntfs/inode.c
> index 9bb9f0952b18..6407af7c2e4f 100644
> --- a/fs/ntfs/inode.c
> +++ b/fs/ntfs/inode.c
> @@ -1810,6 +1810,12 @@ int ntfs_read_inode_mount(struct inode *vi)
> brelse(bh);
> }
>
> + if (m->bytes_allocated != vol->mft_record_size) {
> + ntfs_error(sb, "Incorrect mft record size [%u] in superblock, should be [%u].",
> + m->bytes_allocated, vol->mft_record_size);
> + goto err_out;
> + }
> +
> /* Apply the mst fixups. */
> if (post_read_mst_fixup((NTFS_RECORD*)m, vol->mft_record_size)) {
> /* FIXME: Try to use the $MFTMirr now. */
> --
> 2.28.0
>


--
Anton Altaparmakov <anton at tuxera.com> (replace at with @)
Lead in File System Development, Tuxera Inc., http://www.tuxera.com/
Linux NTFS maintainer