Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1163246AbbKTT7W (ORCPT ); Fri, 20 Nov 2015 14:59:22 -0500 Received: from mail-ig0-f181.google.com ([209.85.213.181]:34056 "EHLO mail-ig0-f181.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1162127AbbKTT7T (ORCPT ); Fri, 20 Nov 2015 14:59:19 -0500 Subject: Re: tty,net: use-after-free in x25_asy_open_tty To: Sasha Levin , gregkh@linuxfoundation.org, Jiri Slaby , David Miller References: <564F26A5.4050905@oracle.com> Cc: LKML , syzkaller@googlegroups.com, "netdev@vger.kernel.org" From: Peter Hurley Message-ID: <564F7B94.3060405@hurleysoftware.com> Date: Fri, 20 Nov 2015 14:59:16 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.3.0 MIME-Version: 1.0 In-Reply-To: <564F26A5.4050905@oracle.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3665 Lines: 91 [ + David Miller ] On 11/20/2015 08:56 AM, Sasha Levin wrote: > Hi all, > > While fuzzing with syzkaller inside a kvmtools guest running latest -next kernel, I've hit: > > [ 634.336761] ================================================================== > [ 634.338226] BUG: KASAN: use-after-free in x25_asy_open_tty+0x13d/0x490 at addr ffff8800a743efd0 > [ 634.339558] Read of size 4 by task syzkaller_execu/8981 > [ 634.340359] ============================================================================= > [ 634.341598] BUG kmalloc-512 (Not tainted): kasan: bad access detected Thanks for the report, Sasha. Would you please test the patch below? The ldisc api should really prevent these kinds of errors. I'll prepare a patch to the tty core which should address the api weakness. Regards, Peter Hurley --->% --- Subject: [PATCH] wan/x25: Fix use-after-free in x25_asy_open_tty() The N_X25 line discipline may access the previous line discipline's closed and already-freed private data on open [1]. The tty->disc_data field _never_ refers to valid data on entry to the line discipline's open() method. Rather, the ldisc is expected to initialize that field for its own use for the lifetime of the instance (ie. from open() to close() only). [1] Report by Sasha Levin [ 634.336761] ================================================================== [ 634.338226] BUG: KASAN: use-after-free in x25_asy_open_tty+0x13d/0x490 at addr ffff8800a743efd0 [ 634.339558] Read of size 4 by task syzkaller_execu/8981 [ 634.340359] ============================================================================= [ 634.341598] BUG kmalloc-512 (Not tainted): kasan: bad access detected ... [ 634.405018] Call Trace: [ 634.405277] dump_stack (lib/dump_stack.c:52) [ 634.405775] print_trailer (mm/slub.c:655) [ 634.406361] object_err (mm/slub.c:662) [ 634.406824] kasan_report_error (mm/kasan/report.c:138 mm/kasan/report.c:236) [ 634.409581] __asan_report_load4_noabort (mm/kasan/report.c:279) [ 634.411355] x25_asy_open_tty (drivers/net/wan/x25_asy.c:559 (discriminator 1)) [ 634.413997] tty_ldisc_open.isra.2 (drivers/tty/tty_ldisc.c:447) [ 634.414549] tty_set_ldisc (drivers/tty/tty_ldisc.c:567) [ 634.415057] tty_ioctl (drivers/tty/tty_io.c:2646 drivers/tty/tty_io.c:2879) [ 634.423524] do_vfs_ioctl (fs/ioctl.c:43 fs/ioctl.c:607) [ 634.427491] SyS_ioctl (fs/ioctl.c:622 fs/ioctl.c:613) [ 634.427945] entry_SYSCALL_64_fastpath (arch/x86/entry/entry_64.S:188) Reported-by: Sasha Levin Signed-off-by: Peter Hurley --- drivers/net/wan/x25_asy.c | 6 +----- 1 file changed, 1 insertion(+), 5 deletions(-) diff --git a/drivers/net/wan/x25_asy.c b/drivers/net/wan/x25_asy.c index 5c47b01..cd39025 100644 --- a/drivers/net/wan/x25_asy.c +++ b/drivers/net/wan/x25_asy.c @@ -549,16 +549,12 @@ static void x25_asy_receive_buf(struct tty_struct *tty, static int x25_asy_open_tty(struct tty_struct *tty) { - struct x25_asy *sl = tty->disc_data; + struct x25_asy *sl; int err; if (tty->ops->write == NULL) return -EOPNOTSUPP; - /* First make sure we're not already connected. */ - if (sl && sl->magic == X25_ASY_MAGIC) - return -EEXIST; - /* OK. Find a free X.25 channel to use. */ sl = x25_asy_alloc(); if (sl == NULL) -- 2.6.3 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/