Re: [PATCH 2/4] xfs: validate inode fork size against fork format

Darrick J. Wong
2022-05-03T22:55:31Z

On Mon, May 02, 2022 at 06:20:16PM +1000, Dave Chinner wrote:
> From: Dave Chinner <dchinner@redhat.com>
>
> xfs_repair catches fork size/format mismatches, but the in-kernel
> verifier doesn't, leading to null pointer failures when attempting
> to perform operations on the fork. This can occur in the
> xfs_dir_is_empty() where the in-memory fork format does not match
> the size and so the fork data pointer is accessed incorrectly.
>
> Note: this causes new failures in xfs/348 which is testing mode vs
> ftype mismatches. We now detect a regular file that has been changed
> to a directory or symlink mode as being corrupt because the data
> fork is for a symlink or directory should be in local form when
> there are only 3 bytes of data in the data fork. Hence the inode
> verify for the regular file now fires w/ -EFSCORRUPTED because
> the inode fork format does not match the format the corrupted mode
> says it should be in.
>
> Signed-off-by: Dave Chinner <dchinner@redhat.com>

/me wonders what the effect this is all going to have on the fuzz vs.
xfs_{scrub,repair} results, but I guess we'll find out in a few weeks.
:P

Reviewed-by: Darrick J. Wong <djwong@kernel.org>

--D

> ---
> fs/xfs/libxfs/xfs_inode_buf.c | 35 ++++++++++++++++++++++++++---------
> 1 file changed, 26 insertions(+), 9 deletions(-)
>
> diff --git a/fs/xfs/libxfs/xfs_inode_buf.c b/fs/xfs/libxfs/xfs_inode_buf.c
> index 74b82ec80f8e..3b1b63f9d886 100644
> --- a/fs/xfs/libxfs/xfs_inode_buf.c
> +++ b/fs/xfs/libxfs/xfs_inode_buf.c
> @@ -357,21 +357,38 @@ xfs_dinode_verify_fork(
> {
> xfs_extnum_t di_nextents;
> xfs_extnum_t max_extents;
> + mode_t mode = be16_to_cpu(dip->di_mode);
> + uint32_t fork_size = XFS_DFORK_SIZE(dip, mp, whichfork);
> + uint32_t fork_format = XFS_DFORK_FORMAT(dip, whichfork);
>
> di_nextents = xfs_dfork_nextents(dip, whichfork);
>
> - switch (XFS_DFORK_FORMAT(dip, whichfork)) {
> + /*
> + * For fork types that can contain local data, check that the fork
> + * format matches the size of local data contained within the fork.
> + *
> + * For all types, check that when the size says the should be in extent
> + * or btree format, the inode isn't claiming it is in local format.
> + */
> + if (whichfork == XFS_DATA_FORK) {
> + if (S_ISDIR(mode) || S_ISLNK(mode)) {
> + if (be64_to_cpu(dip->di_size) <= fork_size &&
> + fork_format != XFS_DINODE_FMT_LOCAL)
> + return __this_address;
> + }
> +
> + if (be64_to_cpu(dip->di_size) > fork_size &&
> + fork_format == XFS_DINODE_FMT_LOCAL)
> + return __this_address;
> + }
> +
> + switch (fork_format) {
> case XFS_DINODE_FMT_LOCAL:
> /*
> - * no local regular files yet
> + * No local regular files yet.
> */
> - if (whichfork == XFS_DATA_FORK) {
> - if (S_ISREG(be16_to_cpu(dip->di_mode)))
> - return __this_address;
> - if (be64_to_cpu(dip->di_size) >
> - XFS_DFORK_SIZE(dip, mp, whichfork))
> - return __this_address;
> - }
> + if (S_ISREG(mode) && whichfork == XFS_DATA_FORK)
> + return __this_address;
> if (di_nextents)
> return __this_address;
> break;
> --
> 2.35.1
>