From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754927AbYCMQh2 (ORCPT ); Thu, 13 Mar 2008 12:37:28 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752216AbYCMQhV (ORCPT ); Thu, 13 Mar 2008 12:37:21 -0400 Received: from sacred.ru ([62.205.161.221]:49796 "EHLO sacred.ru" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752078AbYCMQhU (ORCPT ); Thu, 13 Mar 2008 12:37:20 -0400 Message-ID: <47D95834.8020706@openvz.org> Date: Thu, 13 Mar 2008 19:37:08 +0300 From: Pavel Emelyanov User-Agent: Thunderbird 2.0.0.12 (X11/20080213) MIME-Version: 1.0 To: Andrew Morton , Linux Kernel Mailing List Subject: [PATCH] Avoid potential kernel stack overflow in binfmt_misc.c Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit X-Greylist: Sender succeeded SMTP AUTH authentication, not delayed by milter-greylist-3.0 (sacred.ru [62.205.161.221]); Thu, 13 Mar 2008 19:37:08 +0300 (MSK) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org This can be triggered with root help only, but... Register the ":text:E::txt::/root/cat.txt:' rule in binfmt_misc (by root) and try launching the cat.txt file (by anyone) :) The result is - the endless recursion in the load_misc_binary -> open_exec -> load_misc_binary chain and stack overflow. There's a similar problem with binfmt_script, and there's a sh_bang memner on linux_binprm structure to handle this, but simply raising this in binfmt_misc may break some setups when the interpreter of some misc binaries is a script. So the proposal is to turn sh_bang into a bit, add a new one (the misc_bang) and raise it in load_misc_binary. After this, even if we set up the misc -> script -> misc loop for binfmts one of them will step on its own bang and exit. Signed-off-by: Pavel Emelyanov --- diff --git a/fs/binfmt_em86.c b/fs/binfmt_em86.c index f95ae97..f9c88d0 100644 --- a/fs/binfmt_em86.c +++ b/fs/binfmt_em86.c @@ -43,7 +43,7 @@ static int load_em86(struct linux_binprm *bprm,struct pt_regs *regs) return -ENOEXEC; } - bprm->sh_bang++; /* Well, the bang-shell is implicit... */ + bprm->sh_bang = 1; /* Well, the bang-shell is implicit... */ allow_write_access(bprm->file); fput(bprm->file); bprm->file = NULL; diff --git a/fs/binfmt_misc.c b/fs/binfmt_misc.c index b53c7e5..d7d1b00 100644 --- a/fs/binfmt_misc.c +++ b/fs/binfmt_misc.c @@ -116,6 +116,12 @@ static int load_misc_binary(struct linux_binprm *bprm, struct pt_regs *regs) if (!enabled) goto _ret; + retval = -ENOEXEC; + if (bprm->misc_bang) + goto _ret; + + bprm->misc_bang = 1; + /* to keep locking time low, we copy the interpreter string */ read_lock(&entries_lock); fmt = check_file(bprm); diff --git a/fs/binfmt_script.c b/fs/binfmt_script.c index ab33939..9e3963f 100644 --- a/fs/binfmt_script.c +++ b/fs/binfmt_script.c @@ -29,7 +29,7 @@ static int load_script(struct linux_binprm *bprm,struct pt_regs *regs) * Sorta complicated, but hopefully it will work. -TYT */ - bprm->sh_bang++; + bprm->sh_bang = 1; allow_write_access(bprm->file); fput(bprm->file); bprm->file = NULL; diff --git a/include/linux/binfmts.h b/include/linux/binfmts.h index 1dd7567..b512e48 100644 --- a/include/linux/binfmts.h +++ b/include/linux/binfmts.h @@ -34,7 +34,8 @@ struct linux_binprm{ #endif struct mm_struct *mm; unsigned long p; /* current top of mem */ - int sh_bang; + unsigned int sh_bang:1, + misc_bang:1; struct file * file; int e_uid, e_gid; kernel_cap_t cap_inheritable, cap_permitted;