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SubjectRe: [PATCH -next v3] erofs: Fix pcluster memleak when its block address is zero
Hi all,

On Mon, Dec 05, 2022 at 11:49:57AM +0800, Chen Zhongjin wrote:
> syzkaller reported a memleak:
> https://syzkaller.appspot.com/bug?id=62f37ff612f0021641eda5b17f056f1668aa9aed
>
> unreferenced object 0xffff88811009c7f8 (size 136):
> ...
> backtrace:
> [<ffffffff821db19b>] z_erofs_do_read_page+0x99b/0x1740
> [<ffffffff821dee9e>] z_erofs_readahead+0x24e/0x580
> [<ffffffff814bc0d6>] read_pages+0x86/0x3d0
> ...
>
> syzkaller constructed a case: in z_erofs_register_pcluster(),
> ztailpacking = false and map->m_pa = zero. This makes pcl->obj.index be
> zero although pcl is not a inline pcluster.
>
> Then following path adds refcount for grp, but the refcount won't be put
> because pcl is inline.
>
> z_erofs_readahead()
> z_erofs_do_read_page() # for another page
> z_erofs_collector_begin()
> erofs_find_workgroup()
> erofs_workgroup_get()
>
> Since it's illegal for the block address of a pcluster to be zero, add
> check here to avoid registering the pcluster which would be leaked.
>
> Fixes: cecf864d3d76 ("erofs: support inline data decompression")
> Reported-by: syzbot+6f8cd9a0155b366d227f@syzkaller.appspotmail.com
> Signed-off-by: Chen Zhongjin <chenzhongjin@huawei.com>
> ---
> v1 -> v2:
> As Gao's advice, we should fail to register pcluster if m_pa is zero.
> Maked it this way and changed the commit message.
>
> v2 -> v3:
> Slightly fix commit message and add -next tag.

I've updated the patch itself as below
(Since we only need to fail out for non-tailpacking cases, tailpacking
inline inodes could still have m_pa < EROFS_BLKSIZ):

From f5e037e760d338ca0c116e507be663cb843d42f0 Mon Sep 17 00:00:00 2001
From: Chen Zhongjin <chenzhongjin@huawei.com>
Date: Mon, 5 Dec 2022 11:49:57 +0800
Subject: [PATCH] erofs: Fix pcluster memleak when its block address is zero

syzkaller reported a memleak:
https://syzkaller.appspot.com/bug?id=62f37ff612f0021641eda5b17f056f1668aa9aed

unreferenced object 0xffff88811009c7f8 (size 136):
...
backtrace:
[<ffffffff821db19b>] z_erofs_do_read_page+0x99b/0x1740
[<ffffffff821dee9e>] z_erofs_readahead+0x24e/0x580
[<ffffffff814bc0d6>] read_pages+0x86/0x3d0
...

syzkaller constructed a case: in z_erofs_register_pcluster(),
ztailpacking = false and map->m_pa = zero. This makes pcl->obj.index be
zero although pcl is not a inline pcluster.

Then following path adds refcount for grp, but the refcount won't be put
because pcl is inline.

z_erofs_readahead()
z_erofs_do_read_page() # for another page
z_erofs_collector_begin()
erofs_find_workgroup()
erofs_workgroup_get()

Since it's illegal for the block address of a non-inlined pcluster to
be zero, add check here to avoid registering the pcluster which would
be leaked.

Fixes: cecf864d3d76 ("erofs: support inline data decompression")
Reported-by: syzbot+6f8cd9a0155b366d227f@syzkaller.appspotmail.com
Signed-off-by: Chen Zhongjin <chenzhongjin@huawei.com>
Reviewed-by: Yue Hu <huyue2@coolpad.com>
Reviewed-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
---
fs/erofs/zdata.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/erofs/zdata.c b/fs/erofs/zdata.c
index 2584a62c9d28..fa7ac499a825 100644
--- a/fs/erofs/zdata.c
+++ b/fs/erofs/zdata.c
@@ -496,7 +496,8 @@ static int z_erofs_register_pcluster(struct z_erofs_decompress_frontend *fe)
struct erofs_workgroup *grp;
int err;

- if (!(map->m_flags & EROFS_MAP_ENCODED)) {
+ if (!(map->m_flags & EROFS_MAP_ENCODED) ||
+ (!ztailpacking && !(map->m_pa >> PAGE_SHIFT))) {
DBG_BUGON(1);
return -EFSCORRUPTED;
}
--
2.30.2

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