linux-kernel - [PATCH] proc: fixup empty ARGV case for /proc/$PID/cmdline

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Message-ID: <20150701200403.GA22223@p183.telecom.by>
Date:	Wed, 1 Jul 2015 23:04:03 +0300
From:	Alexey Dobriyan <adobriyan@...il.com>
To:	akpm@...ux-foundation.org
Cc:	linux-kernel@...r.kernel.org
Subject: [PATCH] proc: fixup empty ARGV case for /proc/$PID/cmdline

/proc/*/cmdline code checks if it should look at ENVP area by checking
last byte of ARGV area:

	rv = access_remote_vm(mm, arg_end - 1, &c, 1, 0);
	if (rv <= 0)
		goto out_free_page;

If ARGV is somehow made empty (by doing execve(..., NULL, ...) or
manually setting ->arg_start and ->arg_end to equal values), the decision
will be based on byte which doesn't even belong to ARGV/ENVP.

So, quickly check if ARGV area is empty and report 0 to match previous
behaviour.

Signed-off-by: Alexey Dobriyan <adobriyan@...il.com>
---

 fs/proc/base.c |    5 +++++
 1 file changed, 5 insertions(+)

--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -243,6 +243,11 @@ static ssize_t proc_pid_cmdline_read(struct file *file, char __user *buf,
 	len1 = arg_end - arg_start;
 	len2 = env_end - env_start;
 
+	/* Empty ARGV. */
+	if (len1 == 0) {
+		rv = 0;
+		goto out_free_page;
+	}
 	/*
 	 * Inherently racy -- command line shares address space
 	 * with code and data.
--
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