On Mon, May 26, 2014 at 6:27 AM, Djalal Harouni <tixxdz@xxxxxxxxxx> wrote:
> Add the deny or allow flags, so we can perform proper permission checks
> and set the result accordingly. These flags are needed in case we have
> to cache the result of permission checks that are done during ->open()
> time. Later during ->read(), we can decide to allow or deny the read().
>
> The pid entries that need these flags are:
> /proc/<pid>/stat
> /proc/<pid>/wchan
> /proc/<pid>/maps (will be handled in next patches).
>
> These files are world readable, userspace depend on that. To prevent
> ASLR leaks and to avoid breaking userspace, we follow this scheme:
>
> a) Perform permission checks during ->open()
> b) Cache the result of a) and return success
> c) Recheck the cached result during ->read()
Why is (c) needed?
>
> /*
> + * Flags used to deny or allow current to access /proc/<pid>/$entry
> + * after proper permission checks.
> + */
> +enum {
> + PID_ENTRY_DENY = 0, /* Deny access */
> + PID_ENTRY_ALLOW = 1, /* Allow access */
> +};
I think this would be less alarming if this were:
#define PID_ENTRY_DENY ((void *)1UL)
#define PID_ENTRY_ALLOW ((void *)2UL)
Also, I don't like DENY and ALLOW. It's not denying and allowing.
How about PID_ENTRY_OPENER_MAY_PTRACE and
PID_ENTRY_OPENER_MAY_NOT_PTRACE?
--Andy
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