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 1C0881482E8 for ; Sun, 23 Mar 2025 18:15:05 +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=1742753708; cv=none; b=CXtaynJZ5iadjgBKtsNwIo27d/ES5t4qQXYlsdhk/e66jM/wKlcNACMnzQ9O0QLG6vBFzvKdiF15DiCavXsgpMjEK2+qkqedLcj81WAL0ngpQj4PeS0Qk0eBCqkgZGrZtLKjPsOXwkiBXoCcr2b6a0RIu7b+zZk5ugyhB/l5sKo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1742753708; c=relaxed/simple; bh=6Pr1pJucG4a6OJekUXmBhDG3Cp3c3Z6L8xPwhI0o9rY=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=H7DXrrb4qRNJ24HlrZ/7DPWXjimJVVde8Ovg+YuQ7nIpU+vlZxHNSkxjLmjYAO1jQWNv4NLBRTVv9y3NG3lDy3PLZg/W9xJ6z2OA1z7C4kCS8BtPjlu5kd84AmYzfA3MEN5jd29A432TxJw4dDLYP4OpDp4wEZc0rDzKvDwhOIM= 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=ixiY5+zF; 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="ixiY5+zF" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1742753705; 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=0w5axyZcg98z3a51P4ruVqk9dqgoLr8zEn3jjGLi8f0=; b=ixiY5+zFB1A9nQCHpTseUFAWd1MEetb3SDhgAsKbSAiYdRKZYdAMAkHZjQLV8K9pLw68G8 G2TcjgAdnN5vMpEsaNuvpgfFGnO1mEnZRr5EK7gvZJQ/qjo8M+f52MCfrrToG3k0I/bfDN Xouk9xpZQ2dkaPA2j+levnQLEgB0zfA= Received: from mx-prod-mc-01.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-99-imhGZ1CaPqSBS4hhHCfZrQ-1; Sun, 23 Mar 2025 14:15:01 -0400 X-MC-Unique: imhGZ1CaPqSBS4hhHCfZrQ-1 X-Mimecast-MFC-AGG-ID: imhGZ1CaPqSBS4hhHCfZrQ_1742753699 Received: from mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.4]) (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-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id BD5F0196D2CD; Sun, 23 Mar 2025 18:14:58 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (unknown [10.45.224.42]) by mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with SMTP id 8A03230001A1; Sun, 23 Mar 2025 18:14:55 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Sun, 23 Mar 2025 19:14:25 +0100 (CET) Date: Sun, 23 Mar 2025 19:14:21 +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: <20250323181419.GA14883@redhat.com> References: <67dc67f0.050a0220.25ae54.001f.GAE@google.com> <202503201225.92C5F5FB1@keescook> <20250321-abdecken-infomaterial-2f373f8e3b3c@brauner> <20250322010008.GG2023217@ZenIV> <20250322155538.GA16736@redhat.com> <20250322185007.GI2023217@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: <20250322185007.GI2023217@ZenIV> User-Agent: Mutt/1.5.24 (2015-08-30) X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.4 On 03/22, Al Viro wrote: > > On Sat, Mar 22, 2025 at 04:55:39PM +0100, Oleg Nesterov wrote: > > > And this means that we just need to ensure that ->in_exec is cleared > > before this mutex is dropped, no? Something like below? > > Probably should work, but I wonder if it would be cleaner to have > ->in_exec replaced with pointer to task_struct responsible. Not > "somebody with that fs_struct for ->fs is trying to do execve(), > has verified that nothing outside of their threads is using this > and had been holding ->signal->cred_guard_mutex ever since then", > but "this is the thread that..." perhaps... or something else to make this "not immediately obvious" fs->in_exec more clear. But I guess we need something simple for -stable, so will you agree with this fix for now? Apart from changelog/comments. retval = de_thread(me); + current->fs->in_exec = 0; if (retval) current->fs->in_exec = 0; is correct but looks confusing. See "V2" below, it clears fs->in_exec after the "if (retval)" check. syzbot says: Unfortunately, I don't have any reproducer for this issue yet. so I guess "#syz test: " is pointless right now... Oleg. --- diff --git a/fs/exec.c b/fs/exec.c index 506cd411f4ac..02e8824fc9cd 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -1236,6 +1236,7 @@ int begin_new_exec(struct linux_binprm * bprm) if (retval) goto out; + current->fs->in_exec = 0; /* * Cancel any io_uring activity across execve */ @@ -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;