From patchwork Mon Mar 24 16:00:03 2025 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Oleg Nesterov X-Patchwork-Id: 14027518 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 38B56C36002 for ; Mon, 24 Mar 2025 16:00:55 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 16FAD280002; Mon, 24 Mar 2025 12:00:54 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 11EFC280001; Mon, 24 Mar 2025 12:00:54 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id F28AC280002; Mon, 24 Mar 2025 12:00:53 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0010.hostedemail.com [216.40.44.10]) by kanga.kvack.org (Postfix) with ESMTP id D4CF0280001 for ; Mon, 24 Mar 2025 12:00:53 -0400 (EDT) Received: from smtpin26.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay03.hostedemail.com (Postfix) with ESMTP id 5D7CBAB01F for ; Mon, 24 Mar 2025 16:00:53 +0000 (UTC) X-FDA: 83256907986.26.E9C0F6F Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by imf30.hostedemail.com (Postfix) with ESMTP id 7A96D80015 for ; Mon, 24 Mar 2025 16:00:49 +0000 (UTC) Authentication-Results: imf30.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=DNRS7kbF; dmarc=pass (policy=quarantine) header.from=redhat.com; spf=pass (imf30.hostedemail.com: domain of oleg@redhat.com designates 170.10.133.124 as permitted sender) smtp.mailfrom=oleg@redhat.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1742832050; a=rsa-sha256; cv=none; b=oC38m0ttftlPI9ew/mXB2FPl2cXscCakDZKhu8B7TC8CQP1/Cy9zUseZi0irkSZHvugA6Y iyuHv6i+BqLh7q+ica16D3Ba44PfX93zfqcgG3KRRaPA8oTrCnkTVxEDXadAeaMSOMFc4q VX6T9pzF+UOHK742t0uV8b9PhVVNk60= ARC-Authentication-Results: i=1; imf30.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=DNRS7kbF; dmarc=pass (policy=quarantine) header.from=redhat.com; spf=pass (imf30.hostedemail.com: domain of oleg@redhat.com designates 170.10.133.124 as permitted sender) smtp.mailfrom=oleg@redhat.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1742832050; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=MEzePZHL5YOYb8ZhIKkkzL7fHN+3KRqzc+zq67vlHtI=; b=8oFMv5hPKSsYGIHFY75798axW2VKecsGJecZ1s5tltRlgueZn+/tH/0QHS3aSonu03FuLc NR9XX6hyTkM1WEtbbPXI+OZybjndPJ6/klzLhdjyXXanYVPyh+KKYgXVNmLKH3ycHp/eQq gldNrhrfHgginP2gQr+6yPm0joRLK5Q= DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1742832048; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=MEzePZHL5YOYb8ZhIKkkzL7fHN+3KRqzc+zq67vlHtI=; b=DNRS7kbFIEI7ogsZirioXOqJawxOD8+amXxFMcmYZMFaHmkDO5iA1FlZ7IvvBCrF9wb028 zlPpwxb4jVARiX4fXE3jfvdr4eWmBbFv6lz6RDU+6pCbRVklSXz2xPIivxKGM9E5s2/nOZ GY5RSnKXYrlYRYf4Q7tgN+LP/5RmIE0= Received: from mx-prod-mc-08.mail-002.prod.us-west-2.aws.redhat.com (ec2-35-165-154-97.us-west-2.compute.amazonaws.com [35.165.154.97]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-416-cF6EvRTIOYSZ3zi_G86ECw-1; Mon, 24 Mar 2025 12:00:43 -0400 X-MC-Unique: cF6EvRTIOYSZ3zi_G86ECw-1 X-Mimecast-MFC-AGG-ID: cF6EvRTIOYSZ3zi_G86ECw_1742832042 Received: from mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.111]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 70E571800EC5; Mon, 24 Mar 2025 16:00:41 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (unknown [10.45.224.42]) by mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with SMTP id 7E901180175F; Mon, 24 Mar 2025 16:00:37 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Mon, 24 Mar 2025 17:00:08 +0100 (CET) Date: Mon, 24 Mar 2025 17:00:03 +0100 From: Oleg Nesterov To: syzbot , brauner@kernel.org, kees@kernel.org, viro@zeniv.linux.org.uk Cc: jack@suse.cz, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, syzkaller-bugs@googlegroups.com, mjguzik@gmail.com Subject: [PATCH] exec: fix the racy usage of fs_struct->in_exec Message-ID: <20250324160003.GA8878@redhat.com> References: <67dc67f0.050a0220.25ae54.001f.GAE@google.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <67dc67f0.050a0220.25ae54.001f.GAE@google.com> User-Agent: Mutt/1.5.24 (2015-08-30) X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.111 X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 7A96D80015 X-Stat-Signature: rcpfw155mfr4d8pbbscwzscmou4rfh9d X-Rspam-User: X-HE-Tag: 1742832049-971676 X-HE-Meta: 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 X7nR9J2I 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: check_unsafe_exec() sets fs->in_exec under cred_guard_mutex, then execve() paths clear fs->in_exec lockless. This is fine if exec succeeds, but if it fails we have the following race: T1 sets fs->in_exec = 1, fails, drops cred_guard_mutex T2 sets fs->in_exec = 1 T1 clears fs->in_exec T2 continues with fs->in_exec == 0 Change fs/exec.c to clear fs->in_exec with cred_guard_mutex held. Reported-by: syzbot+1c486d0b62032c82a968@syzkaller.appspotmail.com Closes: https://lore.kernel.org/all/67dc67f0.050a0220.25ae54.001f.GAE@google.com/ Cc: stable@vger.kernel.org Signed-off-by: Oleg Nesterov Acked-by: Kees Cook --- fs/exec.c | 15 +++++++++------ 1 file changed, 9 insertions(+), 6 deletions(-) diff --git a/fs/exec.c b/fs/exec.c index 506cd411f4ac..17047210be46 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -1229,13 +1229,12 @@ int begin_new_exec(struct linux_binprm * bprm) */ bprm->point_of_no_return = true; - /* - * Make this the only thread in the thread group. - */ + /* Make this the only thread in the thread group */ retval = de_thread(me); if (retval) goto out; - + /* see the comment in check_unsafe_exec() */ + current->fs->in_exec = 0; /* * Cancel any io_uring activity across execve */ @@ -1497,6 +1496,8 @@ static void free_bprm(struct linux_binprm *bprm) } free_arg_pages(bprm); if (bprm->cred) { + /* in case exec fails before de_thread() succeeds */ + current->fs->in_exec = 0; mutex_unlock(¤t->signal->cred_guard_mutex); abort_creds(bprm->cred); } @@ -1618,6 +1619,10 @@ static void check_unsafe_exec(struct linux_binprm *bprm) * suid exec because the differently privileged task * will be able to manipulate the current directory, etc. * It would be nice to force an unshare instead... + * + * Otherwise we set fs->in_exec = 1 to deny clone(CLONE_FS) + * from another sub-thread until de_thread() succeeds, this + * state is protected by cred_guard_mutex we hold. */ n_fs = 1; spin_lock(&p->fs->lock); @@ -1862,7 +1867,6 @@ static int bprm_execve(struct linux_binprm *bprm) sched_mm_cid_after_execve(current); /* execve succeeded */ - current->fs->in_exec = 0; current->in_execve = 0; rseq_execve(current); user_events_execve(current); @@ -1881,7 +1885,6 @@ static int bprm_execve(struct linux_binprm *bprm) force_fatal_sig(SIGSEGV); sched_mm_cid_after_execve(current); - current->fs->in_exec = 0; current->in_execve = 0; return retval;