linux-kernel - Re: [PATCH] fs/open: Fix most outstanding security bugs

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Date:   Mon, 1 Apr 2019 10:38:21 -0700
From:   Eric Biggers <ebiggers@...nel.org>
To:     Johannes Thumshirn <jthumshirn@...e.de>
Cc:     Linux Kernel Mailinglist <linux-kernel@...r.kernel.org>,
        Linux FSDEVEL Mailinglist <linux-fsdevel@...r.kernel.org>
Subject: Re: [PATCH] fs/open: Fix most outstanding security bugs

On Mon, Apr 01, 2019 at 11:01:13AM +0200, Johannes Thumshirn wrote:
> Over the last 20 years, the Linux kernel has accumulated hundreds if not
> thousands of security vulnerabilities.
> 
> One common pattern in most of these security related reports is processes
> called "syzkaller", "trinity" or "syz-executor" opening files and then
> abuse kernel interfaces causing kernel crashes or even worse threats using
> memory overwrites or by exploiting race conditions.
> 
> Hunting down these bugs has become time consuming and very expensive, so
> I've decided to put an end to it.
> 
> If one of the above mentioned processes tries opening a file, return -EPERM
> indicating this process does not have the permission to open files on Linux
> anymore.
> 
> Signed-off-by: Johannes Thumshirn <jthumshirn@...e.de>
> ---
>  fs/open.c | 14 ++++++++++++++
>  1 file changed, 14 insertions(+)
> 
> diff --git a/fs/open.c b/fs/open.c
> index f1c2f855fd43..3a3b460beccd 100644
> --- a/fs/open.c
> +++ b/fs/open.c
> @@ -1056,6 +1056,20 @@ long do_sys_open(int dfd, const char __user *filename, int flags, umode_t mode)
>  	struct open_flags op;
>  	int fd = build_open_flags(flags, mode, &op);
>  	struct filename *tmp;
> +	char comm[TASK_COMM_LEN];
> +	int i;
> +	static const char * const list[] = {
> +		"syzkaller",
> +		"syz-executor,"
> +		"trinity",
> +		NULL
> +	};
> +
> +	get_task_comm(comm, current);
> +
> +	for (i = 0; i < ARRAY_SIZE(list); i++)
> +		if (!strncmp(comm, list[i], strlen(list[i])))
> +			return -EPERM;
>  
>  	if (fd)
>  		return fd;
> -- 
> 2.16.4
> 

I like that this can't be circumvented by changing the process name, because it
dereferences a NULL pointer when it gets to the end of the list.  However, I'm a
bit uneasy with updating just this syscall. I suggest we go farther and just do:

diff --git a/init/main.c b/init/main.c
index 598e278b46f7..24f4422cb3c9 100644
--- a/init/main.c
+++ b/init/main.c
@@ -547,6 +547,8 @@ asmlinkage __visible void __init start_kernel(void)
 	char *command_line;
 	char *after_dashes;
 
+	return;
+
 	set_task_stack_end_magic(&init_task);
 	smp_setup_processor_id();
 	debug_objects_early_init();


Please also make sure to add a Reported-by line for each one of the 475 open
syzbot bug reports, so they get properly closed.  Thanks!

- Eric