From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 817BA233149 for ; Sat, 22 Mar 2025 15:56:25 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.129.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1742658987; cv=none; b=gq8KXcQYtT9hmMmtFClhusbF9yD1OgT34ZjDh25MZwk/YTe5vhyeKNigKSWwpRbYBpuGOBIEDveL/D9pU1ZNEDKTPV2kTELKL9enPuFK9+SiyT8ThASf/OWrorwI0AAYMQUBt5K4sTs0P9SQnIkDtLeil97hX5QJng9cm6In7fU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1742658987; c=relaxed/simple; bh=doeceN/js06TXAI4aTf34GgmZWBpDr+yOG2Ab1HJcDY=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=M/kUSNvqgR+cQaT+xdkyJQLyYANKhhfKbp65HBpLZGxm4PdvCS/CF4P+7Cr7Iz4g8O0KCYpJ5T74Y9/v8E3MOkTG2zW6F+UzIU+Z7VG7PArmcN43gqbGYTDdpFaZGp/xzrYpPNp3dZl+o34rUmZW1PXrWuYk1JQKbcSN1b3Lrqc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=GHSzT/oq; arc=none smtp.client-ip=170.10.129.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="GHSzT/oq" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1742658984; 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=/jqIbltbOrjNEWpqd7XmuT8nnchsL9eSWGcr4/X0ZMY=; b=GHSzT/oqEnYBjwLV4klOpyJBJ/n2WeIJd9WmkthGUsWjTkox1aatMyK9thGV+W9vRs5UXy sG0d8RXsG6/yqqcgauhYRftvtxdkoo5O56oVpxD0TMzBe5Xn7vs0a6Da2twAqYR9WAY324 vcmaK7yjEOgT6KXvJoutlJ3+1s6XEik= 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-287-XZvqU3npP-eF51G90MxKQw-1; Sat, 22 Mar 2025 11:56:18 -0400 X-MC-Unique: XZvqU3npP-eF51G90MxKQw-1 X-Mimecast-MFC-AGG-ID: XZvqU3npP-eF51G90MxKQw_1742658977 Received: from mx-prod-int-04.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-04.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.40]) (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 E088E1800EC5; Sat, 22 Mar 2025 15:56:16 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (unknown [10.44.32.40]) by mx-prod-int-04.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with SMTP id A731D19560AF; Sat, 22 Mar 2025 15:56:13 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Sat, 22 Mar 2025 16:55:44 +0100 (CET) Date: Sat, 22 Mar 2025 16:55:39 +0100 From: Oleg Nesterov To: Al Viro Cc: Christian Brauner , Kees Cook , jack@suse.cz, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, syzkaller-bugs@googlegroups.com, syzbot Subject: Re: [syzbot] [fs?] [mm?] KCSAN: data-race in bprm_execve / copy_fs (4) Message-ID: <20250322155538.GA16736@redhat.com> References: <67dc67f0.050a0220.25ae54.001f.GAE@google.com> <202503201225.92C5F5FB1@keescook> <20250321-abdecken-infomaterial-2f373f8e3b3c@brauner> <20250322010008.GG2023217@ZenIV> Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250322010008.GG2023217@ZenIV> User-Agent: Mutt/1.5.24 (2015-08-30) X-Scanned-By: MIMEDefang 3.0 on 10.30.177.40 Quite possibly I am wrong, I need to recall this code, but at first glance... On 03/22, Al Viro wrote: > > Not really. I agree, it is really racy. But, > 1) A enters check_unsafe_execve(), sets ->in_exec to 1 > 2) B enters check_unsafe_execve(), sets ->in_exec to 1 No, check_unsafe_execve() is called with cred_guard_mutex held, see prepare_bprm_creds() > 3) A calls exec_binprm(), fails (bad binary) > 4) A clears ->in_exec So (2) can only happen after A fails and drops cred_guard_mutex. And this means that we just need to ensure that ->in_exec is cleared before this mutex is dropped, no? Something like below? Oleg. --- diff --git a/fs/exec.c b/fs/exec.c index 506cd411f4ac..f8bf3c96e181 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -1233,6 +1233,7 @@ int begin_new_exec(struct linux_binprm * bprm) * Make this the only thread in the thread group. */ retval = de_thread(me); + current->fs->in_exec = 0; if (retval) goto out; @@ -1497,6 +1498,8 @@ static void free_bprm(struct linux_binprm *bprm) } free_arg_pages(bprm); if (bprm->cred) { + // for the case exec fails before de_thread() + current->fs->in_exec = 0; mutex_unlock(¤t->signal->cred_guard_mutex); abort_creds(bprm->cred); } @@ -1862,7 +1865,6 @@ 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 +1883,6 @@ 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;