linux-kernel - Re: [PATCH] Set bounds on what /proc/self/make-it-fail accepts.

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Message-Id: <20140219134025.fcd70941e1ec98723a1bd230@linux-foundation.org>
Date:	Wed, 19 Feb 2014 13:40:25 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Dave Jones <davej@...hat.com>
Cc:	Linux Kernel <linux-kernel@...r.kernel.org>,
	Al Viro <viro@...iv.linux.org.uk>,
	David Rientjes <rientjes@...gle.com>,
	Akinobu Mita <akinobu.mita@...il.com>
Subject: Re: [PATCH] Set bounds on what /proc/self/make-it-fail accepts.

On Tue, 18 Feb 2014 17:06:06 -0500 Dave Jones <davej@...hat.com> wrote:

> /proc/self/make-it-fail is a boolean, but accepts any number, including
> negative ones. Change variable to unsigned, and cap upper bound at 1.
> 
> Signed-off-by: Dave Jones <davej@...oraproject.org>
> 
> diff --git a/fs/proc/base.c b/fs/proc/base.c
> index 51507065263b..b926377c354f 100644
> --- a/fs/proc/base.c
> +++ b/fs/proc/base.c
> @@ -1207,7 +1207,7 @@ static ssize_t proc_fault_inject_read(struct file * file, char __user * buf,
>  	struct task_struct *task = get_proc_task(file_inode(file));
>  	char buffer[PROC_NUMBUF];
>  	size_t len;
> -	int make_it_fail;
> +	unsigned int make_it_fail;
>  
>  	if (!task)
>  		return -ESRCH;
> @@ -1224,7 +1224,7 @@ static ssize_t proc_fault_inject_write(struct file * file,
>  {
>  	struct task_struct *task;
>  	char buffer[PROC_NUMBUF], *end;
> -	int make_it_fail;
> +	unsigned int make_it_fail;
>  
>  	if (!capable(CAP_SYS_RESOURCE))
>  		return -EPERM;
> @@ -1236,6 +1236,9 @@ static ssize_t proc_fault_inject_write(struct file * file,
>  	make_it_fail = simple_strtol(strstrip(buffer), &end, 0);
>  	if (*end)
>  		return -EINVAL;
> +	if (make_it_fail > 1)
> +		return -EINVAL;
> +
>  	task = get_proc_task(file_inode(file));
>  	if (!task)
>  		return -ESRCH;

Switching `make_it_fail' to unsigned makes the test simpler but it does
rather muck up the typing in there.  task_struct.make_it_fail is still
an int, we should now use simple_strtoul rather than simple_strtol,
proc_fault_inject_read()'s snprintf() should now use %u, etc.  None of
which actually matters, but still...

Rather than address all that I'm inclined to leave `make_it_fail' as an
int, turning your patch into a one-liner?

--- a/fs/proc/base.c~fault-injection-set-bounds-on-what-proc-self-make-it-fail-accepts-fix
+++ a/fs/proc/base.c
@@ -1207,7 +1207,7 @@ static ssize_t proc_fault_inject_read(st
 	struct task_struct *task = get_proc_task(file_inode(file));
 	char buffer[PROC_NUMBUF];
 	size_t len;
-	unsigned int make_it_fail;
+	int make_it_fail;
 
 	if (!task)
 		return -ESRCH;
@@ -1224,7 +1224,7 @@ static ssize_t proc_fault_inject_write(s
 {
 	struct task_struct *task;
 	char buffer[PROC_NUMBUF], *end;
-	unsigned int make_it_fail;
+	int make_it_fail;
 
 	if (!capable(CAP_SYS_RESOURCE))
 		return -EPERM;
@@ -1236,7 +1236,7 @@ static ssize_t proc_fault_inject_write(s
 	make_it_fail = simple_strtol(strstrip(buffer), &end, 0);
 	if (*end)
 		return -EINVAL;
-	if (make_it_fail > 1)
+	if (make_it_fail < 0 || make_it_fail > 1)
 		return -EINVAL;
 
 	task = get_proc_task(file_inode(file));
_

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