2019-04-18 08:33:35

by Pan Bian

Subject: ext4: avoid drop reference to iloc.bh twice

The reference to iloc.bh has been dropped in ext4_mark_iloc_dirty.
However, the reference is dropped again if error occurs during
ext4_handle_dirty_metadata, which may result in use-after-free bugs.

Fixes: fb265c9cb49e("ext4: add ext4_sb_bread() to disambiguate ENOMEM
cases")

Signed-off-by: Pan Bian <[email protected]>
---
fs/ext4/resize.c | 1 +
1 file changed, 1 insertion(+)

diff --git a/fs/ext4/resize.c b/fs/ext4/resize.c
index e7ae26e..4d5c0fc 100644
--- a/fs/ext4/resize.c
+++ b/fs/ext4/resize.c
@@ -874,6 +874,7 @@ static int add_new_gdb(handle_t *handle, struct inode *inode,
err = ext4_handle_dirty_metadata(handle, NULL, gdb_bh);
if (unlikely(err)) {
ext4_std_error(sb, err);
+ iloc.bh = NULL;
goto errout;
}
brelse(dind);
--
2.7.4

2019-04-18 12:37:32

by Jan Kara

Subject: Re: ext4: avoid drop reference to iloc.bh twice

On Thu 18-04-19 16:31:18, Pan Bian wrote:
> The reference to iloc.bh has been dropped in ext4_mark_iloc_dirty.
> However, the reference is dropped again if error occurs during
> ext4_handle_dirty_metadata, which may result in use-after-free bugs.
>
> Fixes: fb265c9cb49e("ext4: add ext4_sb_bread() to disambiguate ENOMEM
> cases")
>
> Signed-off-by: Pan Bian <[email protected]>

Thanks for the patch! Good spotting. You can add:

Reviewed-by: Jan Kara <[email protected]>

I'm just wondering: Ted, shouldn't we make ext4_mark_iloc_dirty() clear the
iloc.bh pointer on it's own? I believe this is not the first time we had a
bug like this and it would also catch possible use-after-free issues in
case someone tried to use iloc.bh after the reference has been dropped.

Generally the scheme around ext4_get_inode_loc() and
ext4_mark_iloc_dirty() seems to be somewhat error prone. E.g. a quick audit
shows that there's bh leak in ext4_orphan_del() in one of the error paths.
I'll send patches.

Honza

> ---
> fs/ext4/resize.c | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/fs/ext4/resize.c b/fs/ext4/resize.c
> index e7ae26e..4d5c0fc 100644
> --- a/fs/ext4/resize.c
> +++ b/fs/ext4/resize.c
> @@ -874,6 +874,7 @@ static int add_new_gdb(handle_t *handle, struct inode *inode,
> err = ext4_handle_dirty_metadata(handle, NULL, gdb_bh);
> if (unlikely(err)) {
> ext4_std_error(sb, err);
> + iloc.bh = NULL;
> goto errout;
> }
> brelse(dind);
> --
> 2.7.4
>
>
--
Jan Kara <[email protected]>
SUSE Labs, CR