[PATCH] ext4: check iomap type only if ext4_iomap_begin() does not fail

[PATCH] ext4: check iomap type only if ext4_iomap_begin() does not fail

[Baokun Li]

When ext4_iomap_overwrite_begin() calls ext4_iomap_begin() map blocks may
fail for some reason (e.g. memory allocation failure, bare disk write), and
later because "iomap->type ! = IOMAP_MAPPED" triggers WARN_ON(). When ext4
iomap_begin() returns an error, it is normal that the type of iomap->type
may not match the expectation. Therefore, we only determine if iomap->type
is as expected when ext4_iomap_begin() is executed successfully.

Reported-by: syzbot+08106c4b7d60702dbc14@syzkaller.appspotmail.com
Link: https://lore.kernel.org/all/00000000000015760b05f9b4eee9@google.com
Signed-off-by: Baokun Li <libaokun1@huawei.com>
---
 fs/ext4/inode.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 0d5ba922e411..19c884abe52b 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -3375,7 +3375,7 @@ static int ext4_iomap_overwrite_begin(struct inode *inode, loff_t offset,
 	 */
 	flags &= ~IOMAP_WRITE;
 	ret = ext4_iomap_begin(inode, offset, length, flags, iomap, srcmap);
-	WARN_ON_ONCE(iomap->type != IOMAP_MAPPED);
+	WARN_ON_ONCE(!ret && iomap->type != IOMAP_MAPPED);
 	return ret;
 }
 
-- 
2.31.1

Re: [PATCH] ext4: check iomap type only if ext4_iomap_begin() does not fail

[Jan Kara]

On Fri 05-05-23 21:24:29, Baokun Li wrote:
> When ext4_iomap_overwrite_begin() calls ext4_iomap_begin() map blocks may
> fail for some reason (e.g. memory allocation failure, bare disk write), and
> later because "iomap->type ! = IOMAP_MAPPED" triggers WARN_ON(). When ext4
> iomap_begin() returns an error, it is normal that the type of iomap->type
> may not match the expectation. Therefore, we only determine if iomap->type
> is as expected when ext4_iomap_begin() is executed successfully.
> 
> Reported-by: syzbot+08106c4b7d60702dbc14@syzkaller.appspotmail.com
> Link: https://lore.kernel.org/all/00000000000015760b05f9b4eee9@google.com
> Signed-off-by: Baokun Li <libaokun1@huawei.com>

Makes sense. Feel free to add:

Reviewed-by: Jan Kara <jack@suse.cz>

								Honza

> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index 0d5ba922e411..19c884abe52b 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -3375,7 +3375,7 @@ static int ext4_iomap_overwrite_begin(struct inode *inode, loff_t offset,
>  	 */
>  	flags &= ~IOMAP_WRITE;
>  	ret = ext4_iomap_begin(inode, offset, length, flags, iomap, srcmap);
> -	WARN_ON_ONCE(iomap->type != IOMAP_MAPPED);
> +	WARN_ON_ONCE(!ret && iomap->type != IOMAP_MAPPED);
>  	return ret;
>  }
>  
> -- 
> 2.31.1
> 
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR

Re: [PATCH] ext4: check iomap type only if ext4_iomap_begin() does not fail

[Theodore Ts'o]

On Fri, 05 May 2023 21:24:29 +0800, Baokun Li wrote:
> When ext4_iomap_overwrite_begin() calls ext4_iomap_begin() map blocks may
> fail for some reason (e.g. memory allocation failure, bare disk write), and
> later because "iomap->type ! = IOMAP_MAPPED" triggers WARN_ON(). When ext4
> iomap_begin() returns an error, it is normal that the type of iomap->type
> may not match the expectation. Therefore, we only determine if iomap->type
> is as expected when ext4_iomap_begin() is executed successfully.
> 
> [...]

Applied, thanks!

[1/1] ext4: check iomap type only if ext4_iomap_begin() does not fail
      commit: 705c514635a4b6fd0ee321bcf1a9bd75c3629b71

Best regards,
-- 
Theodore Ts'o <tytso@mit.edu>