2022-12-05 15:38:46

by Gao Xiang

Subject: [PATCH 2/2] erofs: validate the extent length for uncompressed pclusters

syzkaller reported a KASAN use-after-free:
https://syzkaller.appspot.com/bug?extid=2ae90e873e97f1faf6f2

The referenced fuzzed image actually has two issues:
- m_pa == 0 as a non-inlined pcluster;
- The logical length is longer than its physical length.

The first issue has already been addressed. This patch addresses
the second issue by checking the extent length validity.

Reported-by: [email protected]
Fixes: 02827e1796b3 ("staging: erofs: add erofs_map_blocks_iter")
Signed-off-by: Gao Xiang <[email protected]>
---
fs/erofs/zmap.c | 5 +++++
1 file changed, 5 insertions(+)

diff --git a/fs/erofs/zmap.c b/fs/erofs/zmap.c
index 98eff1259de4..0150570c33aa 100644
--- a/fs/erofs/zmap.c
+++ b/fs/erofs/zmap.c
@@ -698,6 +698,11 @@ static int z_erofs_do_map_blocks(struct inode *inode,
}

if (m.headtype == Z_EROFS_VLE_CLUSTER_TYPE_PLAIN) {
+ if (map->m_llen > map->m_plen) {
+ DBG_BUGON(1);
+ err = -EFSCORRUPTED;
+ goto unmap_out;
+ }
if (vi->z_advise & Z_EROFS_ADVISE_INTERLACED_PCLUSTER)
map->m_algorithmformat =
Z_EROFS_COMPRESSION_INTERLACED;
--
2.24.4

2022-12-06 15:24:32

by Chao Yu

Subject: Re: [PATCH 2/2] erofs: validate the extent length for uncompressed pclusters

On 2022/12/5 23:00, Gao Xiang wrote:
> syzkaller reported a KASAN use-after-free:
> https://syzkaller.appspot.com/bug?extid=2ae90e873e97f1faf6f2
>
> The referenced fuzzed image actually has two issues:
> - m_pa == 0 as a non-inlined pcluster;
> - The logical length is longer than its physical length.
>
> The first issue has already been addressed. This patch addresses
> the second issue by checking the extent length validity.
>
> Reported-by: [email protected]
> Fixes: 02827e1796b3 ("staging: erofs: add erofs_map_blocks_iter")
> Signed-off-by: Gao Xiang <[email protected]>

Reviewed-by: Chao Yu <[email protected]>

Thanks,