Re: [PATCH v3] fs: introduce pipe-only dump mode suid_dumpable=3

[Andrew Morton <akpm@linux-foundation.org>]

On Fri, 22 Jun 2012 12:24:13 -0700
Kees Cook <keescook@chromium.org> wrote:

> The value
> of suid_dumpable=2 is now historic, and attempting to set this sysctl
> value returns -EINVAL.

This sounds a bit harsh - will it not cause existing configurations to
immediately break?  If so, would it not be better to retain the =2 mode
for a while, and emit a nice warning when it is set?

>
> ...
>
> +/* Allow only the valid suid_dumpable values. */
> +static int do_proc_dointvec_suid_dumpable_conv(bool *negp,
> +		unsigned long *lvalp, int *valp, int write, void *data)
> +{
> +	if (write) {
> +		int val = *negp ? -*lvalp : *lvalp;
> +		if (val != SUID_DUMPABLE_DISABLED &&
> +		    val != SUID_DUMPABLE_ENABLED &&
> +		    val != SUID_DUMPABLE_PIPE_ONLY)
> +			return -EINVAL;
> +		*valp = val;
> +	} else {
> +		int val = *valp;
> +		if (val < 0) {
> +			*negp = true;
> +			*lvalp = (unsigned long)-val;
> +		} else {
> +			*negp = false;
> +			*lvalp = (unsigned long)val;

Those two typecasts are unneeded.

> +		}
> +	}
> +	return 0;
> +}
> +