linux-kernel - [PATCH] proc: make proc_fd_permission() thread-friendly

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: <20130826175441.GA28856@redhat.com>
Date:	Mon, 26 Aug 2013 19:54:41 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Willy Tarreau <w@....eu>, Al Viro <viro@...iv.linux.org.uk>,
	Andy Lutomirski <luto@...capital.net>,
	Ingo Molnar <mingo@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linux FS Devel <linux-fsdevel@...r.kernel.org>,
	Brad Spengler <spender@...ecurity.net>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>
Subject: [PATCH] proc: make proc_fd_permission() thread-friendly

proc_fd_permission() says "process can still access /proc/self/fd
after it has executed a setuid()", but the "task_pid() = proc_pid()
check only helps if the task is group leader, /proc/self points to
/proc/leader-pid.

Change this check to use task_tgid() so that the whole process can
access /proc/self/fd.

Note: CLONE_THREAD doesn't require CLONE_FILES so task->files can
differ, but I don't think this can lead to any security problem.

Test-case:

	void *tfunc(void *arg)
	{
		assert(opendir("/proc/self/fd"));
		return NULL;
	}

	int main(void)
	{
		pthread_t t;
		pthread_create(&t, NULL, tfunc, NULL);
		pthread_join(t, NULL);
		return 0;
	}

fails if, say, this executable is not readable and suid_dumpable = 0.

Signed-off-by: Oleg Nesterov <oleg@...hat.com>
---
 fs/proc/fd.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/fs/proc/fd.c b/fs/proc/fd.c
index 0ff80f9..985ea88 100644
--- a/fs/proc/fd.c
+++ b/fs/proc/fd.c
@@ -286,7 +286,7 @@ int proc_fd_permission(struct inode *inode, int mask)
 	int rv = generic_permission(inode, mask);
 	if (rv == 0)
 		return 0;
-	if (task_pid(current) == proc_pid(inode))
+	if (task_tgid(current) == proc_pid(inode))
 		rv = 0;
 	return rv;
 }
-- 
1.5.5.1


--
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/