linux-kernel - [PATCH] Fix error handling in begin_new

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Date:   Sun, 6 Jun 2021 12:41:18 +0200
From:   Bernd Edlinger <bernd.edlinger@...mail.de>
To:     Alexander Viro <viro@...iv.linux.org.uk>,
        Kees Cook <keescook@...omium.org>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: [PATCH] Fix error handling in begin_new_exec

If get_unused_fd_flags() fails, the error handling is incomplete
because bprm->cred is already set to NULL, and therefore
free_bprm will not unlock the cred_guard_mutex.
Note there are two error conditions which end up here,
one before and one after bprm->cred is cleared.

Fixes: b8a61c9e7b4 ("exec: Generic execfd support")

Signed-off-by: Bernd Edlinger <bernd.edlinger@...mail.de>
---
 fs/exec.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/fs/exec.c b/fs/exec.c
index 18594f1..d8af85f 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1396,6 +1396,9 @@ int begin_new_exec(struct linux_binprm * bprm)
 
 out_unlock:
 	up_write(&me->signal->exec_update_lock);
+	if (!bprm->cred)
+		mutex_unlock(&me->signal->cred_guard_mutex);
+
 out:
 	return retval;
 }
-- 
1.9.1