Re: [PATCH] xfs: fix overflow in xfs_attr3_leaf_verify

["Darrick J. Wong" <darrick.wong@oracle.com>]

On Fri, Nov 02, 2018 at 03:31:16PM +1100, Dave Chinner wrote:
> From: Dave Chinner <dchinner@redhat.com>
> 
> generic/070 on 64k block size filesystems is failing with a verifier
> corruption on writeback or an attribute leaf block:
> 
> [   94.973083] XFS (pmem0): Metadata corruption detected at xfs_attr3_leaf_verify+0x246/0x260, xfs_attr3_leaf block 0x811480
> [   94.975623] XFS (pmem0): Unmount and run xfs_repair
> [   94.976720] XFS (pmem0): First 128 bytes of corrupted metadata buffer:
> [   94.978270] 000000004b2e7b45: 00 00 00 00 00 00 00 00 3b ee 00 00 00 00 00 00  ........;.......
> [   94.980268] 000000006b1db90b: 00 00 00 00 00 81 14 80 00 00 00 00 00 00 00 00  ................
> [   94.982251] 00000000433f2407: 22 7b 5c 82 2d 5c 47 4c bb 31 1c 37 fa a9 ce d6  "{\.-\GL.1.7....
> [   94.984157] 0000000010dc7dfb: 00 00 00 00 00 81 04 8a 00 0a 18 e8 dd 94 01 00  ................
> [   94.986215] 00000000d5a19229: 00 a0 dc f4 fe 98 01 68 f0 d8 07 e0 00 00 00 00  .......h........
> [   94.988171] 00000000521df36c: 0c 2d 32 e2 fe 20 01 00 0c 2d 58 65 fe 0c 01 00  .-2.. ...-Xe....
> [   94.990162] 000000008477ae06: 0c 2d 5b 66 fe 8c 01 00 0c 2d 71 35 fe 7c 01 00  .-[f.....-q5.|..
> [   94.992139] 00000000a4a6bca6: 0c 2d 72 37 fc d4 01 00 0c 2d d8 b8 f0 90 01 00  .-r7.....-......
> [   94.994789] XFS (pmem0): xfs_do_force_shutdown(0x8) called from line 1453 of file fs/xfs/xfs_buf.c. Return address = ffffffff815365f3
> 
> This is failing this check:
> 
>                 end = ichdr.freemap[i].base + ichdr.freemap[i].size;
>                 if (end < ichdr.freemap[i].base)
> >>>>>                   return __this_address;
>                 if (end > mp->m_attr_geo->blksize)
>                         return __this_address;
> 
> And from the buffer output above, the freemap array is:
> 
> 	freemap[0].base = 0x00a0
> 	freemap[0].size = 0xdcf4	end = 0xdd94
> 	freemap[1].base = 0xfe98
> 	freemap[1].size = 0x0168	end = 0x10000
> 	freemap[2].base = 0xf0d8
> 	freemap[2].size = 0x07e0	end = 0xf8b8
> 
> These all look valid - the block size is 0x10000 and so from the
> last check in the above verifier fragment we know that the end
> of freemap[1] is valid. The problem is that end is declared as:
> 
> 	uint16_t	end;
> 
> And (uint16_t)0x10000 = 0. So we have a verifier bug here, not a
> corruption. Fix the verifier to use uint32_t types for the check and
> hence avoid the overflow.
> 
> Fixes: https://bugzilla.kernel.org/show_bug.cgi?id=201577
> Signed-off-by: Dave Chinner <dchinner@redhat.com>

DOH. :(

Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>

--D

> ---
>  fs/xfs/libxfs/xfs_attr_leaf.c | 11 +++++++++--
>  1 file changed, 9 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/xfs/libxfs/xfs_attr_leaf.c b/fs/xfs/libxfs/xfs_attr_leaf.c
> index 6fc5425b1474..2652d00842d6 100644
> --- a/fs/xfs/libxfs/xfs_attr_leaf.c
> +++ b/fs/xfs/libxfs/xfs_attr_leaf.c
> @@ -243,7 +243,7 @@ xfs_attr3_leaf_verify(
>  	struct xfs_mount		*mp = bp->b_target->bt_mount;
>  	struct xfs_attr_leafblock	*leaf = bp->b_addr;
>  	struct xfs_attr_leaf_entry	*entries;
> -	uint16_t			end;
> +	uint32_t			end;	/* must be 32bit - see below */
>  	int				i;
>  
>  	xfs_attr3_leaf_hdr_from_disk(mp->m_attr_geo, &ichdr, leaf);
> @@ -293,6 +293,11 @@ xfs_attr3_leaf_verify(
>  	/*
>  	 * Quickly check the freemap information.  Attribute data has to be
>  	 * aligned to 4-byte boundaries, and likewise for the free space.
> +	 *
> +	 * Note that for 64k block size filesystems, the freemap entries cannot
> +	 * overflow as they are only be16 fields. However, when checking end
> +	 * pointer of the freemap, we have to be careful to detect overflows and
> +	 * so use uint32_t for those checks.
>  	 */
>  	for (i = 0; i < XFS_ATTR_LEAF_MAPSIZE; i++) {
>  		if (ichdr.freemap[i].base > mp->m_attr_geo->blksize)
> @@ -303,7 +308,9 @@ xfs_attr3_leaf_verify(
>  			return __this_address;
>  		if (ichdr.freemap[i].size & 0x3)
>  			return __this_address;
> -		end = ichdr.freemap[i].base + ichdr.freemap[i].size;
> +
> +		/* be care of 16 bit overflows here */
> +		end = (uint32_t)ichdr.freemap[i].base + ichdr.freemap[i].size;
>  		if (end < ichdr.freemap[i].base)
>  			return __this_address;
>  		if (end > mp->m_attr_geo->blksize)
> -- 
> 2.19.1
>