linux-kernel - Re: [PATCH -next v3] erofs: Fix pcluster memleak when its block address is zero

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Date:   Mon, 5 Dec 2022 14:08:15 +0800
From:   Gao Xiang <xiang@...nel.org>
To:     Chen Zhongjin <chenzhongjin@...wei.com>, huyue2@...lpad.com
Cc:     syzbot+6f8cd9a0155b366d227f@...kaller.appspotmail.com,
        linux-erofs@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        xiang@...nel.org, chao@...nel.org, jefflexu@...ux.alibaba.com
Subject: Re: [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@...kaller.appspotmail.com
> Signed-off-by: Chen Zhongjin <chenzhongjin@...wei.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@...wei.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@...kaller.appspotmail.com
Signed-off-by: Chen Zhongjin <chenzhongjin@...wei.com>
Reviewed-by: Yue Hu <huyue2@...lpad.com>
Reviewed-by: Gao Xiang <hsiangkao@...ux.alibaba.com>
Signed-off-by: Gao Xiang <hsiangkao@...ux.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