linux-kernel - [PATCH 3.13.y-ckt 137/139] mnt: Fix a memory stomp in umount

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 for Android: free password hash cracker in your pocket

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

Message-Id: <1422483682-15393-138-git-send-email-kamal@canonical.com>
Date:	Wed, 28 Jan 2015 14:21:20 -0800
From:	Kamal Mostafa <kamal@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Kamal Mostafa <kamal@...onical.com>
Subject: [PATCH 3.13.y-ckt 137/139] mnt: Fix a memory stomp in umount

3.13.11-ckt15 -stable review patch.  If anyone has any objections, please let me know.

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

From: "Eric W. Biederman" <ebiederm@...ssion.com>

commit c297abfdf15b4480704d6b566ca5ca9438b12456 upstream.

While reviewing the code of umount_tree I realized that when we append
to a preexisting unmounted list we do not change pprev of the former
first item in the list.

Which means later in namespace_unlock hlist_del_init(&mnt->mnt_hash) on
the former first item of the list will stomp unmounted.first leaving
it set to some random mount point which we are likely to free soon.

This isn't likely to hit, but if it does I don't know how anyone could
track it down.

[ This happened because we don't have all the same operations for
  hlist's as we do for normal doubly-linked lists. In particular,
  list_splice() is easy on our standard doubly-linked lists, while
  hlist_splice() doesn't exist and needs both start/end entries of the
  hlist.  And commit 38129a13e6e7 incorrectly open-coded that missing
  hlist_splice().

  We should think about making these kinds of "mindless" conversions
  easier to get right by adding the missing hlist helpers   - Linus ]

Fixes: 38129a13e6e71f666e0468e99fdd932a687b4d7e switch mnt_hash to hlist
Signed-off-by: "Eric W. Biederman" <ebiederm@...ssion.com>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Kamal Mostafa <kamal@...onical.com>
---
 fs/namespace.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/fs/namespace.c b/fs/namespace.c
index a67e3c0..289c216 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -1286,6 +1286,8 @@ void umount_tree(struct mount *mnt, int how)
 	}
 	if (last) {
 		last->mnt_hash.next = unmounted.first;
+		if (unmounted.first)
+			unmounted.first->pprev = &last->mnt_hash.next;
 		unmounted.first = tmp_list.first;
 		unmounted.first->pprev = &unmounted.first;
 	}
-- 
1.9.1

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/