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SubjectRe: [Cluster-devel] [PATCH] gfs2: gfs2_read_sb: put gfs2_assert inside the loop
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On 03/10/2020 07:31, Fox Chen wrote:
> for (x = 2;; x++) {
> ...
> gfs2_assert(sdp, x <= GFS2_MAX_META_HEIGHT); <--- after
> ...
> if (d != sdp->sd_heightsize[x - 1] || m)
> break;
> sdp->sd_heightsize[x] = space;
> }
>
> sdp->sd_max_height = x
> gfs2_assert(sdp, sdp->sd_max_height <= GFS2_MAX_META_HEIGHT) <--- before
>
> Before this patch, gfs2_assert is put outside of the loop of
> sdp->sd_heightsize[x] calculation. When something goes wrong,

So this looks related to one of the recent syzbot reports, where the
"something goes wrong" is the block size in the on-disk superblock was
zeroed and that leads eventually to this out-of-bounds write. The
correct fix in that case would be to add a validity check for the block
size in gfs2_check_sb().

Andy

> x exceeds the size of GFS2_MAX_META_HEIGHT, it may already crash inside
> the loop when
>
> sdp->sd_heightsize[x] = space
>
> tries to reach the out-of-bound
> location, gfs2_assert won't help here.
>
> This patch fixes this by moving gfs2_assert into the loop.
> We will check x value each time to see if it exceeds GFS2_MAX_META_HEIGHT.
>
> Signed-off-by: Fox Chen <foxhlchen@gmail.com>
> ---
> fs/gfs2/ops_fstype.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/fs/gfs2/ops_fstype.c b/fs/gfs2/ops_fstype.c
> index 6d18d2c91add..6cc32e3010f2 100644
> --- a/fs/gfs2/ops_fstype.c
> +++ b/fs/gfs2/ops_fstype.c
> @@ -333,6 +333,7 @@ static int gfs2_read_sb(struct gfs2_sbd *sdp, int silent)
> u64 space, d;
> u32 m;
>
> + gfs2_assert(sdp, x <= GFS2_MAX_META_HEIGHT);
> space = sdp->sd_heightsize[x - 1] * sdp->sd_inptrs;
> d = space;
> m = do_div(d, sdp->sd_inptrs);
> @@ -343,7 +344,6 @@ static int gfs2_read_sb(struct gfs2_sbd *sdp, int silent)
> }
> sdp->sd_max_height = x;
> sdp->sd_heightsize[x] = ~0;
> - gfs2_assert(sdp, sdp->sd_max_height <= GFS2_MAX_META_HEIGHT);
>
> sdp->sd_max_dents_per_leaf = (sdp->sd_sb.sb_bsize -
> sizeof(struct gfs2_leaf)) /
>

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