linux-kernel - [PATCH 3.16 103/136] ceph: fix use-after-free in __ceph_remove

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <lsq.1576543535.425487150@decadent.org.uk>
Date:   Tue, 17 Dec 2019 00:47:17 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, Denis Kirjanov <kda@...ux-powerpc.org>,
        "Luis Henriques" <lhenriques@...e.com>,
        "Ilya Dryomov" <idryomov@...il.com>,
        "Jeff Layton" <jlayton@...nel.org>
Subject: [PATCH 3.16 103/136] ceph: fix use-after-free in __ceph_remove_cap()

3.16.80-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Luis Henriques <lhenriques@...e.com>

commit ea60ed6fcf29eebc78f2ce91491e6309ee005a01 upstream.

KASAN reports a use-after-free when running xfstest generic/531, with the
following trace:

[  293.903362]  kasan_report+0xe/0x20
[  293.903365]  rb_erase+0x1f/0x790
[  293.903370]  __ceph_remove_cap+0x201/0x370
[  293.903375]  __ceph_remove_caps+0x4b/0x70
[  293.903380]  ceph_evict_inode+0x4e/0x360
[  293.903386]  evict+0x169/0x290
[  293.903390]  __dentry_kill+0x16f/0x250
[  293.903394]  dput+0x1c6/0x440
[  293.903398]  __fput+0x184/0x330
[  293.903404]  task_work_run+0xb9/0xe0
[  293.903410]  exit_to_usermode_loop+0xd3/0xe0
[  293.903413]  do_syscall_64+0x1a0/0x1c0
[  293.903417]  entry_SYSCALL_64_after_hwframe+0x44/0xa9

This happens because __ceph_remove_cap() may queue a cap release
(__ceph_queue_cap_release) which can be scheduled before that cap is
removed from the inode list with

	rb_erase(&cap->ci_node, &ci->i_caps);

And, when this finally happens, the use-after-free will occur.

This can be fixed by removing the cap from the inode list before being
removed from the session list, and thus eliminating the risk of an UAF.

Signed-off-by: Luis Henriques <lhenriques@...e.com>
Reviewed-by: Jeff Layton <jlayton@...nel.org>
Signed-off-by: Ilya Dryomov <idryomov@...il.com>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 fs/ceph/caps.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

--- a/fs/ceph/caps.c
+++ b/fs/ceph/caps.c
@@ -913,6 +913,11 @@ void __ceph_remove_cap(struct ceph_cap *
 
 	dout("__ceph_remove_cap %p from %p\n", cap, &ci->vfs_inode);
 
+	/* remove from inode's cap rbtree, and clear auth cap */
+	rb_erase(&cap->ci_node, &ci->i_caps);
+	if (ci->i_auth_cap == cap)
+		ci->i_auth_cap = NULL;
+
 	/* remove from session list */
 	spin_lock(&session->s_cap_lock);
 	/*
@@ -939,11 +944,6 @@ void __ceph_remove_cap(struct ceph_cap *
 	cap->ci = NULL;
 	spin_unlock(&session->s_cap_lock);
 
-	/* remove from inode list */
-	rb_erase(&cap->ci_node, &ci->i_caps);
-	if (ci->i_auth_cap == cap)
-		ci->i_auth_cap = NULL;
-
 	if (removed)
 		ceph_put_cap(mdsc, cap);