Ocfs2 devel - May 2023 - [PATCH] ocfs2: fix use-after-free when unmounting read-only filesystem

It's trivial to trigger a use-after-free bug in the ocfs2 quotas code using
fstest generic/452.  After mounting a filesystem as read-only, quotas are
suspended and ocfs2_mem_dqinfo is freed through ->ocfs2_local_free_info(). 
When
unmounting the filesystem, an UAF access to the oinfo will eventually cause a
crash.

Cc: <stable at vger.kernel.org>
Signed-off-by: Lu?s Henriques <lhenriques at suse.de>
---
 fs/ocfs2/super.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/fs/ocfs2/super.c b/fs/ocfs2/super.c
index 0b0e6a132101..988d1c076861 100644
--- a/fs/ocfs2/super.c
+++ b/fs/ocfs2/super.c
@@ -952,8 +952,10 @@ static void ocfs2_disable_quotas(struct ocfs2_super *osb)
 	for (type = 0; type < OCFS2_MAXQUOTAS; type++) {
 		if (!sb_has_quota_loaded(sb, type))
 			continue;
-		oinfo = sb_dqinfo(sb, type)->dqi_priv;
-		cancel_delayed_work_sync(&oinfo->dqi_sync_work);
+		if (!sb_has_quota_suspended(sb, type)) {
+			oinfo = sb_dqinfo(sb, type)->dqi_priv;
+			cancel_delayed_work_sync(&oinfo->dqi_sync_work);
+		}
 		inode = igrab(sb->s_dquot.files[type]);
 		/* Turn off quotas. This will remove all dquot structures from
 		 * memory and so they will be automatically synced to global

On 5/22/23 6:25 PM, Lu?s Henriques wrote:
> It's trivial to trigger a use-after-free bug in the ocfs2 quotas code
using
> fstest generic/452.  After mounting a filesystem as read-only, quotas are
generic/452 is for testing ext4 mounted with dax and ro.
But ocfs2 doesn't support dax yet. 
> suspended and ocfs2_mem_dqinfo is freed through
->ocfs2_local_free_info().  When
> unmounting the filesystem, an UAF access to the oinfo will eventually cause
a
> crash.
In ocfs2_fill_super(), it won't enable quota if is a readonly mount.
Do you mean remount as readonly?

Thanks,
Joseph
> 
> Cc: <stable at vger.kernel.org>
> Signed-off-by: Lu?s Henriques <lhenriques at suse.de>
> ---
>  fs/ocfs2/super.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/ocfs2/super.c b/fs/ocfs2/super.c
> index 0b0e6a132101..988d1c076861 100644
> --- a/fs/ocfs2/super.c
> +++ b/fs/ocfs2/super.c
> @@ -952,8 +952,10 @@ static void ocfs2_disable_quotas(struct ocfs2_super
*osb)
>  	for (type = 0; type < OCFS2_MAXQUOTAS; type++) {
>  		if (!sb_has_quota_loaded(sb, type))
>  			continue;
> -		oinfo = sb_dqinfo(sb, type)->dqi_priv;
> -		cancel_delayed_work_sync(&oinfo->dqi_sync_work);
> +		if (!sb_has_quota_suspended(sb, type)) {
> +			oinfo = sb_dqinfo(sb, type)->dqi_priv;
> +			cancel_delayed_work_sync(&oinfo->dqi_sync_work);
> +		}
>  		inode = igrab(sb->s_dquot.files[type]);
>  		/* Turn off quotas. This will remove all dquot structures from
>  		 * memory and so they will be automatically synced to global