[J][PATCH v2 1/1] gfs2: Fix slab-use-after-free in gfs2_qd_dealloc

[Yuxuan Luo]

From: Juntong Deng <juntong.deng at outlook.com>

In gfs2_put_super(), whether withdrawn or not, the quota should
be cleaned up by gfs2_quota_cleanup().

Otherwise, struct gfs2_sbd will be freed before gfs2_qd_dealloc (rcu
callback) has run for all gfs2_quota_data objects, resulting in
use-after-free.

Also, gfs2_destroy_threads() and gfs2_quota_cleanup() is already called
by gfs2_make_fs_ro(), so in gfs2_put_super(), after calling
gfs2_make_fs_ro(), there is no need to call them again.

Reported-by: syzbot+29c47e9e51895928698c at syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=29c47e9e51895928698c
Signed-off-by: Juntong Deng <juntong.deng at outlook.com>
Signed-off-by: Andreas Gruenbacher <agruenba at redhat.com>
(backported from commit bdcb8aa434c6d36b5c215d02a9ef07551be25a37)
[yuxuan.luo:
The fix commit, bdcb8aa434c6 ("gfs2: Fix slab-use-after-free in
gfs2_qd_dealloc"), addresses two problems:

1) UAF caused by gfs2_quota_cleanup() not called if not already
withdrawn "[otherwise], struct gfs2_sbd will be freed before
gfs2_qd_dealloc (rcu callback) has run for all gfs2_quota_data objects".
2) Double-free by calling gfs2_quota_cleanup() twice if in not read-only
mode.

The second issue is introduced by f66af88e3321 ("gfs2: Stop using
gfs2_make_fs_ro for withdraw") and not affecting this kernel while the
first one does. To solve the first one, only call the
gfs2_quota_cleanup() if the gfs2_make_fs_ro() is not called since
gfs2_make_fs_ro() calls gfs2_quota_cleanup() as well.
]
CVE-2023-52760
Signed-off-by: Yuxuan Luo <yuxuan.luo at canonical.com>
---
 fs/gfs2/super.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/fs/gfs2/super.c b/fs/gfs2/super.c
index 268651ac9fc84..98158559893f4 100644
--- a/fs/gfs2/super.c
+++ b/fs/gfs2/super.c
@@ -590,6 +590,8 @@ static void gfs2_put_super(struct super_block *sb)
 
 	if (!sb_rdonly(sb)) {
 		gfs2_make_fs_ro(sdp);
+	} else {
+		gfs2_quota_cleanup(sdp);
 	}
 	WARN_ON(gfs2_withdrawing(sdp));
 
-- 
2.34.1