Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757955Ab3CDERW (ORCPT ); Sun, 3 Mar 2013 23:17:22 -0500 Received: from shadbolt.e.decadent.org.uk ([88.96.1.126]:60816 "EHLO shadbolt.e.decadent.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754823Ab3CDDmn (ORCPT ); Sun, 3 Mar 2013 22:42:43 -0500 Message-Id: <20130304033722.200526197@decadent.org.uk> User-Agent: quilt/0.60-1 Date: Mon, 04 Mar 2013 03:39:36 +0000 From: Ben Hutchings To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: akpm@linux-foundation.org, Kees Cook , halfdog , P J P , Alexander Viro Subject: [ 149/153] exec: use -ELOOP for max recursion depth In-Reply-To: <20130304033707.648729212@decadent.org.uk> X-SA-Exim-Connect-IP: 2001:470:1f08:1539:a11:96ff:fec6:70c4 X-SA-Exim-Mail-From: ben@decadent.org.uk X-SA-Exim-Scanned: No (on shadbolt.decadent.org.uk); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4508 Lines: 143 3.2-stable review patch. If anyone has any objections, please let me know. ------------------ From: Kees Cook commit d740269867021faf4ce38a449353d2b986c34a67 upstream. To avoid an explosion of request_module calls on a chain of abusive scripts, fail maximum recursion with -ELOOP instead of -ENOEXEC. As soon as maximum recursion depth is hit, the error will fail all the way back up the chain, aborting immediately. This also has the side-effect of stopping the user's shell from attempting to reexecute the top-level file as a shell script. As seen in the dash source: if (cmd != path_bshell && errno == ENOEXEC) { *argv-- = cmd; *argv = cmd = path_bshell; goto repeat; } The above logic was designed for running scripts automatically that lacked the "#!" header, not to re-try failed recursion. On a legitimate -ENOEXEC, things continue to behave as the shell expects. Additionally, when tracking recursion, the binfmt handlers should not be involved. The recursion being tracked is the depth of calls through search_binary_handler(), so that function should be exclusively responsible for tracking the depth. Signed-off-by: Kees Cook Cc: halfdog Cc: P J P Cc: Alexander Viro Signed-off-by: Andrew Morton [bwh: Backported to 3.2: adjust context] Signed-off-by: Ben Hutchings --- fs/binfmt_em86.c | 1 - fs/binfmt_misc.c | 6 ------ fs/binfmt_script.c | 4 +--- fs/exec.c | 10 +++++----- include/linux/binfmts.h | 2 -- 5 files changed, 6 insertions(+), 17 deletions(-) --- a/fs/binfmt_em86.c +++ b/fs/binfmt_em86.c @@ -42,7 +42,6 @@ static int load_em86(struct linux_binprm return -ENOEXEC; } - bprm->recursion_depth++; /* Well, the bang-shell is implicit... */ allow_write_access(bprm->file); fput(bprm->file); bprm->file = NULL; --- a/fs/binfmt_misc.c +++ b/fs/binfmt_misc.c @@ -116,10 +116,6 @@ static int load_misc_binary(struct linux if (!enabled) goto _ret; - retval = -ENOEXEC; - if (bprm->recursion_depth > BINPRM_MAX_RECURSION) - goto _ret; - /* to keep locking time low, we copy the interpreter string */ read_lock(&entries_lock); fmt = check_file(bprm); @@ -199,8 +195,6 @@ static int load_misc_binary(struct linux if (retval < 0) goto _error; - bprm->recursion_depth++; - retval = search_binary_handler (bprm, regs); if (retval < 0) goto _error; --- a/fs/binfmt_script.c +++ b/fs/binfmt_script.c @@ -22,15 +22,13 @@ static int load_script(struct linux_binp char interp[BINPRM_BUF_SIZE]; int retval; - if ((bprm->buf[0] != '#') || (bprm->buf[1] != '!') || - (bprm->recursion_depth > BINPRM_MAX_RECURSION)) + if ((bprm->buf[0] != '#') || (bprm->buf[1] != '!')) return -ENOEXEC; /* * This section does the #! interpretation. * Sorta complicated, but hopefully it will work. -TYT */ - bprm->recursion_depth++; allow_write_access(bprm->file); fput(bprm->file); bprm->file = NULL; --- a/fs/exec.c +++ b/fs/exec.c @@ -1385,6 +1385,10 @@ int search_binary_handler(struct linux_b struct linux_binfmt *fmt; pid_t old_pid; + /* This allows 4 levels of binfmt rewrites before failing hard. */ + if (depth > 5) + return -ELOOP; + retval = security_bprm_check(bprm); if (retval) return retval; @@ -1408,12 +1412,8 @@ int search_binary_handler(struct linux_b if (!try_module_get(fmt->module)) continue; read_unlock(&binfmt_lock); + bprm->recursion_depth = depth + 1; retval = fn(bprm, regs); - /* - * Restore the depth counter to its starting value - * in this call, so we don't have to rely on every - * load_binary function to restore it on return. - */ bprm->recursion_depth = depth; if (retval >= 0) { if (depth == 0) --- a/include/linux/binfmts.h +++ b/include/linux/binfmts.h @@ -67,8 +67,6 @@ struct linux_binprm { #define BINPRM_FLAGS_EXECFD_BIT 1 #define BINPRM_FLAGS_EXECFD (1 << BINPRM_FLAGS_EXECFD_BIT) -#define BINPRM_MAX_RECURSION 4 - /* Function parameter for binfmt->coredump */ struct coredump_params { long signr; -- 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/