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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> 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 X-Rspamd-Queue-Id: 3FF79C0003 X-Rspamd-Server: rspam05 X-Rspam-User: X-Stat-Signature: as996hwr8qedjkp8wkycqpjk7d5d1dh8 X-HE-Tag: 1742658981-978637 X-HE-Meta: U2FsdGVkX1/MMVrhch3c3Vdk9njURzBfgg6otkEyIB24aWt5sEgO1gyNCfiKNh7ANbKYAkPMCoJq/JK+dqyQkK9ZekuhtnD1wWIqoNGas0+mSl9koALTVhpgM5c3Vf0b+1a2YaFIOS05V2zAejO6oUMZILT6cbUJzKKr+psbGVSzewzdnYz0N9+yPDBrRUD1rCpYqQpWylRIpo8JmflUXm+aUMCmV+GsloJH/iEiYVCndt1dMejJqUwH+YYURGKSLuXgp4hpsr3FBLgQ2FE3PMVvRjKrw4cZHNAmzsYp1rH8vcMcCGZ/qDWk5yVnLHshqHxmLEnlxwTNjz1vIRg+q9Odn6qFjJrU9QDKDlXIf7oLi4OdBFqILv5HWPBgUfKjgBA9ddM6G2we2+goaLlLlriOpAecrJCOlkwTEzzw+AqIXQTxXz5CRTIz8N8k8RrAhFrz76X9FqNdXWfuvNly3S+r+zq4tpoWSR2BdC7astJjkPmZad94VdgZHjecmWWuwPf43NS/r5yQ7AMztY+3E56r7LEBmTf5kNFayhAbM8owAJwkkYFjl40poxhCpNgtTM6yeRvkyOTAZQz5i8koZwUATVoYg2CZhSaU/TPYAe1H3dkfCCZwjxYXawFUgAajTc/YXVTK+b+mk4evGooLOD6FnaiDdRzmSp0zYtyjpS5gogm0I8LFoQciRFESagcXxywn4tCCZN53xcaUfphumvo/UZBU1fdN18ZE0fRdvJM1zycKDOMErekJ5vfO43fwtW2zC/7kFqahgor3MYj1tHJngS4nNXeiWObSYYAml3EAiZcxzh+2Gt9AWUN+sKRYtftsfl9XEcHzoj2+2UOZgEmEriMAKHYth57mLLWJofo0YCTy8Mbkwbz/SpVzbV1NWe9BjChvDCQcBNT6cmwLQ3Pt6ZDH+RwTSS/fduybpwYLxjDw9dxZwIjiOP5feP5a3Qdl9jvAoTow/ic8yuK Z3J/P7md 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000001, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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;