linux-kernel - [PATCH] umh: fix memory leak on execve failure

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Message-Id: <20200507221422.19338-1-v.minet@criteo.com>
Date:   Fri,  8 May 2020 00:14:22 +0200
From:   Vincent Minet <v.minet@...teo.com>
To:     bpf@...r.kernel.org
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        Alexei Starovoitov <ast@...nel.org>,
        Luis Chamberlain <mcgrof@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Vincent Minet <v.minet@...teo.com>
Subject: [PATCH] umh: fix memory leak on execve failure

If a UMH process created by fork_usermode_blob() fails to execute,
a pair of struct file allocated by umh_pipe_setup() will leak.

Under normal conditions, the caller (like bpfilter) needs to manage the
lifetime of the UMH and its two pipes. But when fork_usermode_blob()
fails, the caller doesn't really have a way to know what needs to be
done. It seems better to do the cleanup ourselves in this case.

Fixes: 449325b52b7a ("umh: introduce fork_usermode_blob() helper")
Signed-off-by: Vincent Minet <v.minet@...teo.com>
---
 kernel/umh.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/kernel/umh.c b/kernel/umh.c
index 7f255b5a8845..20d51e0957e0 100644
--- a/kernel/umh.c
+++ b/kernel/umh.c
@@ -475,6 +475,12 @@ static void umh_clean_and_save_pid(struct subprocess_info *info)
 {
 	struct umh_info *umh_info = info->data;
 
+	/* cleanup if umh_pipe_setup() was successful but exec failed */
+	if (info->pid && info->retval) {
+		fput(umh_info->pipe_to_umh);
+		fput(umh_info->pipe_from_umh);
+	}
+
 	argv_free(info->argv);
 	umh_info->pid = info->pid;
 }
-- 
2.26.2