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From:   ebiederm@xmission.com (Eric W. Biederman)
To:     <linux-kernel@vger.kernel.org>
Cc:     Linus Torvalds <torvalds@linux-foundation.org>,
        Oleg Nesterov <oleg@redhat.com>, Jann Horn <jannh@google.com>,
        Kees Cook <keescook@chromium.org>,
        Greg Ungerer <gerg@linux-m68k.org>,
        Rob Landley <rob@landley.net>,
        Bernd Edlinger <bernd.edlinger@hotmail.de>,
        <linux-fsdevel@vger.kernel.org>, Al Viro <viro@ZenIV.linux.org.uk>,
        Alexey Dobriyan <adobriyan@gmail.com>,
        Andrew Morton <akpm@linux-foundation.org>
References: <87h7wujhmz.fsf@x220.int.ebiederm.org>
Date:   Tue, 05 May 2020 14:41:47 -0500
In-Reply-To: <87h7wujhmz.fsf@x220.int.ebiederm.org> (Eric W. Biederman's
        message of "Tue, 05 May 2020 14:39:32 -0500")
Message-ID: <875zdajhj8.fsf@x220.int.ebiederm.org>
User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.1 (gnu/linux)
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Subject: [PATCH 2/7] exec: Make unlocking exec_update_mutex explict
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk


With install_exec_creds updated to follow immediately after
setup_new_exec, the failure of unshare_sighand is the only
code path where exec_update_mutex is held but not explicitly
unlocked.

Update that code path to explicitly unlock exec_update_mutex.

Remove the unlocking of exec_update_mutex from free_bprm.

Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
---
 fs/exec.c               | 6 +++---
 include/linux/binfmts.h | 3 +--
 2 files changed, 4 insertions(+), 5 deletions(-)

diff --git a/fs/exec.c b/fs/exec.c
index 06b4c550af5d..6bd82a007bfc 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1344,7 +1344,7 @@ int flush_old_exec(struct linux_binprm * bprm)
 	 */
 	retval = unshare_sighand(me);
 	if (retval)
-		goto out;
+		goto out_unlock;
 
 	set_fs(USER_DS);
 	me->flags &= ~(PF_RANDOMIZE | PF_FORKNOEXEC | PF_KTHREAD |
@@ -1361,6 +1361,8 @@ int flush_old_exec(struct linux_binprm * bprm)
 	do_close_on_exec(me->files);
 	return 0;
 
+out_unlock:
+	mutex_unlock(&me->signal->exec_update_mutex);
 out:
 	return retval;
 }
@@ -1477,8 +1479,6 @@ static void free_bprm(struct linux_binprm *bprm)
 {
 	free_arg_pages(bprm);
 	if (bprm->cred) {
-		if (bprm->called_exec_mmap)
-			mutex_unlock(&current->signal->exec_update_mutex);
 		mutex_unlock(&current->signal->cred_guard_mutex);
 		abort_creds(bprm->cred);
 	}
diff --git a/include/linux/binfmts.h b/include/linux/binfmts.h
index a345d9fed3d8..6f564b9ad882 100644
--- a/include/linux/binfmts.h
+++ b/include/linux/binfmts.h
@@ -47,8 +47,7 @@ struct linux_binprm {
 		secureexec:1,
 		/*
 		 * Set by flush_old_exec, when exec_mmap has been called.
-		 * This is past the point of no return, when the
-		 * exec_update_mutex has been taken.
+		 * This is past the point of no return.
 		 */
 		called_exec_mmap:1;
 #ifdef __alpha__
-- 
2.20.1