On Sat 11-09-21 17:00:57, Ye Bin wrote:
> As call read_mmp_block pass bh_check which value is NULL, then call
> sb_getblk to get buffer_head. But mmp_block's buffer_head is already exist
> which also is uptodate. Lead to compare the same data.
>
> Signed-off-by: Ye Bin <yebin10@xxxxxxxxxx>
This looks good, except that read_mmp_block() also releases bh it is passed
in case of error. So it can free buffer head which is still referenced from
EXT4_SB(sb)->s_mmp_bh and cause use-after-free issues.
I guess I would just get rid of sb_getblk() in read_mmp_block() and always
expect valid bh passed. The only place that passes NULL bh after this
patch is one case in ext4_multi_mount_protect() and that can call
sb_getblk() on its own. That way we can also simplify read_mmp_block()
prototype to:
static int read_mmp_block(struct super_block *sb, struct buffer_head *bh);
Honza
> ---
> fs/ext4/mmp.c | 17 ++++++-----------
> 1 file changed, 6 insertions(+), 11 deletions(-)
>
> diff --git a/fs/ext4/mmp.c b/fs/ext4/mmp.c
> index 4433fe7e9e86..007bde3c12b8 100644
> --- a/fs/ext4/mmp.c
> +++ b/fs/ext4/mmp.c
> @@ -213,10 +213,7 @@ static int kmmpd(void *data)
> * we need to check if the MMP block is as we write it.
> */
> if (jiffies - last_check_time > mmp_check_interval * HZ) {
> - struct buffer_head *bh_check = NULL;
> - struct mmp_struct *mmp_check;
> -
> - retval = read_mmp_block(sb, &bh_check, mmp_block);
> + retval = read_mmp_block(sb, &bh, mmp_block);
> if (retval) {
> ext4_error_err(sb, -retval,
> "error reading MMP data: %d",
> @@ -224,20 +221,18 @@ static int kmmpd(void *data)
> goto wait_to_exit;
> }
>
> - mmp_check = (struct mmp_struct *)(bh_check->b_data);
> - if (seq != mmp_check->mmp_seq ||
> - memcmp(nodename, mmp_check->mmp_nodename,
> - sizeof(mmp->mmp_nodename))) {
> - dump_mmp_msg(sb, mmp_check,
> + mmp = (struct mmp_struct *)(bh->b_data);
> + if (seq != le32_to_cpu(mmp->mmp_seq) ||
> + memcmp(nodename, mmp->mmp_nodename,
> + sizeof(nodename))) {
> + dump_mmp_msg(sb, mmp,
> "Error while updating MMP info. "
> "The filesystem seems to have been"
> " multiply mounted.");
> ext4_error_err(sb, EBUSY, "abort");
> - put_bh(bh_check);
> retval = -EBUSY;
> goto wait_to_exit;
> }
> - put_bh(bh_check);
> last_check_time = jiffies;
> }
>
> --
> 2.31.1
>
--
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR
