[PATCH] ext4: Make sanity check in mballoc more strict

[PATCH] ext4: Make sanity check in mballoc more strict

[Jan Kara]

Sanity check in mb_find_extent() only checked that returned extent does
not extend past blocksize * 8, however it should not extend past
EXT4_CLUSTERS_PER_GROUP(sb). This can happen when clusters_per_group <
blocksize * 8 and the tail of the bitmap is not properly filled by 1s
which happened e.g. when ancient kernels have grown the filesystem.

Signed-off-by: Jan Kara <jack@suse.cz>
---
 fs/ext4/mballoc.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

As a background: We have a customer who has filesystems (created & apparently
resized by 3.0 or older kernels) and which make current kernels eventually barf
with errors but e2fsck says everything is fine.  This patch makes mballoc code
detect issues earlier. I'll send appropriate e2fsck patch shortly.

diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index 6fb76d408093..8ef5f12bbee2 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -1539,7 +1539,7 @@ static int mb_find_extent(struct ext4_buddy *e4b, int block,
 		ex->fe_len += 1 << order;
 	}
 
-	if (ex->fe_start + ex->fe_len > (1 << (e4b->bd_blkbits + 3))) {
+	if (ex->fe_start + ex->fe_len > EXT4_CLUSTERS_PER_GROUP(e4b->bd_sb)) {
 		/* Should never happen! (but apparently sometimes does?!?) */
 		WARN_ON(1);
 		ext4_error(e4b->bd_sb, "corruption or bug in mb_find_extent "
-- 
2.16.4

Re: [PATCH] ext4: Make sanity check in mballoc more strict

[Theodore Ts'o]

On Thu, Mar 28, 2019 at 05:41:17PM +0100, Jan Kara wrote:
> Sanity check in mb_find_extent() only checked that returned extent does
> not extend past blocksize * 8, however it should not extend past
> EXT4_CLUSTERS_PER_GROUP(sb). This can happen when clusters_per_group <
> blocksize * 8 and the tail of the bitmap is not properly filled by 1s
> which happened e.g. when ancient kernels have grown the filesystem.
> 
> Signed-off-by: Jan Kara <jack@suse.cz>

Thanks, applied.

					- Ted