Re: [RFC PATCH] xfs: don't run off the end of the buffer reading inline dirents

[Brian Foster <bfoster@redhat.com>]

On Wed, Mar 08, 2017 at 01:01:12PM -0800, Darrick J. Wong wrote:
> Check that we don't run off the end of the inline data buffer when we're
> trying to read directory entries.  xfs/348 triggered kernel memory being
> exposed to userspace and a related complaint from the usercopy code.
> 
> Evidently once we call dir_emit, the VFS ignores error return values
> since it's already begun copying data back to userspace.
> 

How do we get into this situation in the first place?

> Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
> ---
>  fs/xfs/xfs_dir2_readdir.c |    8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/fs/xfs/xfs_dir2_readdir.c b/fs/xfs/xfs_dir2_readdir.c
> index 003a99b..70bdd21 100644
> --- a/fs/xfs/xfs_dir2_readdir.c
> +++ b/fs/xfs/xfs_dir2_readdir.c
> @@ -69,6 +69,7 @@ xfs_dir2_sf_getdents(
>  	xfs_dir2_dataptr_t	dotdot_offset;
>  	xfs_ino_t		ino;
>  	struct xfs_da_geometry	*geo = args->geo;
> +	char *endp;
>  
>  	ASSERT(dp->i_df.if_flags & XFS_IFINLINE);
>  	/*
> @@ -83,6 +84,7 @@ xfs_dir2_sf_getdents(
>  	ASSERT(dp->i_df.if_u1.if_data != NULL);
>  
>  	sfp = (xfs_dir2_sf_hdr_t *)dp->i_df.if_u1.if_data;
> +	endp = dp->i_df.if_u1.if_data + dp->i_df.if_bytes;
>  
>  	if (dp->i_d.di_size < xfs_dir2_sf_hdr_size(sfp->i8count))
>  		return -EFSCORRUPTED;
> @@ -130,6 +132,12 @@ xfs_dir2_sf_getdents(
>  	for (i = 0; i < sfp->count; i++) {
>  		__uint8_t filetype;
>  
> +		/* If we pass the end of the buffer, we're done. */
> +		if (((char *)sfep + sizeof(*sfep)) >= endp ||
> +		    (char *)dp->d_ops->sf_nextentry(sfp, sfep) > endp) {
> +			break;
> +		}
> +

What's the reason for checking ->sf_nextentry()?

Brian

>  		off = xfs_dir2_db_off_to_dataptr(geo, geo->datablk,
>  				xfs_dir2_sf_get_offset(sfep));
>  
> --
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