From patchwork Wed Dec 19 12:42:00 2012 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Luis Henriques X-Patchwork-Id: 207337 Return-Path: X-Original-To: incoming@patchwork.ozlabs.org Delivered-To: patchwork-incoming@bilbo.ozlabs.org Received: from chlorine.canonical.com (chlorine.canonical.com [91.189.94.204]) by ozlabs.org (Postfix) with ESMTP id 3D8752C007B for ; Wed, 19 Dec 2012 23:42:22 +1100 (EST) Received: from localhost ([127.0.0.1] helo=chlorine.canonical.com) by chlorine.canonical.com with esmtp (Exim 4.71) (envelope-from ) id 1TlIyR-0002OU-2Z; Wed, 19 Dec 2012 12:42:11 +0000 Received: from youngberry.canonical.com ([91.189.89.112]) by chlorine.canonical.com with esmtp (Exim 4.71) (envelope-from ) id 1TlIyO-0002No-SZ for kernel-team@lists.ubuntu.com; Wed, 19 Dec 2012 12:42:08 +0000 Received: from bl20-141-18.dsl.telepac.pt ([2.81.141.18] helo=localhost) by youngberry.canonical.com with esmtpsa (TLS1.0:DHE_RSA_AES_128_CBC_SHA1:16) (Exim 4.71) (envelope-from ) id 1TlIyO-0004fr-Gf for kernel-team@lists.ubuntu.com; Wed, 19 Dec 2012 12:42:08 +0000 From: Luis Henriques To: kernel-team@lists.ubuntu.com Subject: [Oneiric][CVE] exec: use -ELOOP for max recursion depth Date: Wed, 19 Dec 2012 12:42:00 +0000 Message-Id: <1355920923-23703-4-git-send-email-luis.henriques@canonical.com> X-Mailer: git-send-email 1.7.10.4 In-Reply-To: <1355920923-23703-1-git-send-email-luis.henriques@canonical.com> References: <1355920923-23703-1-git-send-email-luis.henriques@canonical.com> X-BeenThere: kernel-team@lists.ubuntu.com X-Mailman-Version: 2.1.13 Precedence: list List-Id: Kernel team discussions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , MIME-Version: 1.0 Sender: kernel-team-bounces@lists.ubuntu.com Errors-To: kernel-team-bounces@lists.ubuntu.com From: Kees Cook CVE-2012-4530 BugLink: http://bugs.launchpad.net/bugs/1068888 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 Signed-off-by: Linus Torvalds (backported from commit d740269867021faf4ce38a449353d2b986c34a67) Conflicts: fs/binfmt_misc.c fs/exec.c Signed-off-by: Luis Henriques --- fs/binfmt_em86.c | 1 - fs/binfmt_misc.c | 8 +------- fs/binfmt_script.c | 4 +--- fs/exec.c | 10 +++++----- include/linux/binfmts.h | 2 -- 5 files changed, 7 insertions(+), 18 deletions(-) diff --git a/fs/binfmt_em86.c b/fs/binfmt_em86.c index b8e8b0a..4a1b984 100644 --- a/fs/binfmt_em86.c +++ b/fs/binfmt_em86.c @@ -42,7 +42,6 @@ static int load_em86(struct linux_binprm *bprm,struct pt_regs *regs) return -ENOEXEC; } - bprm->recursion_depth++; /* 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 5463952..82b4456 100644 --- a/fs/binfmt_misc.c +++ b/fs/binfmt_misc.c @@ -116,10 +116,6 @@ static int load_misc_binary(struct linux_binprm *bprm, struct pt_regs *regs) 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); @@ -200,9 +196,7 @@ static int load_misc_binary(struct linux_binprm *bprm, struct pt_regs *regs) if (retval < 0) goto _error; - bprm->recursion_depth++; - - retval = search_binary_handler (bprm, regs); + retval = search_binary_handler(bprm, regs); if (retval < 0) goto _error; diff --git a/fs/binfmt_script.c b/fs/binfmt_script.c index e39c18a..211ede0 100644 --- a/fs/binfmt_script.c +++ b/fs/binfmt_script.c @@ -22,15 +22,13 @@ static int load_script(struct linux_binprm *bprm,struct pt_regs *regs) 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; diff --git a/fs/exec.c b/fs/exec.c index f7af22b..3558306 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -1373,6 +1373,10 @@ int search_binary_handler(struct linux_binprm *bprm,struct pt_regs *regs) int try,retval; struct linux_binfmt *fmt; + /* This allows 4 levels of binfmt rewrites before failing hard. */ + if (depth > 5) + return -ELOOP; + retval = security_bprm_check(bprm); if (retval) return retval; @@ -1391,12 +1395,8 @@ int search_binary_handler(struct linux_binprm *bprm,struct pt_regs *regs) 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) diff --git a/include/linux/binfmts.h b/include/linux/binfmts.h index 384e37f..718eb0b 100644 --- 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;