Re: [Qemu-devel] [PATCH v2] linux-user: fix is_proc_myself to check the paths via realpath

[Zach Riggle]

Friendly ping :)

I've updated the patch with v2 which addresses the style issue


*Zach Riggle*

On Tue, Oct 24, 2017 at 10:34 PM, Zach Riggle <address@hidden> wrote:

> Previously, it was possible to get a handle to the "real" /proc/self/mem
> by creating a symlink to it and opening the symlink, or opening e.g.
> "./mem" after chdir'ing to "/proc/self".
>
>     $ ln -s /proc/self self
>     $ cat self/maps
>     60000000-602bc000 r-xp 00000000 fc:01 270375
>    /usr/bin/qemu-arm-static
>     604bc000-6050f000 rw-p 002bc000 fc:01 270375
>    /usr/bin/qemu-arm-static
>     ...
>
> Signed-off-by: Zach Riggle <address@hidden>
> ---
>  linux-user/syscall.c | 47 ++++++++++++++++++++++++++++-------------------
>  1 file changed, 28 insertions(+), 19 deletions(-)
>
> diff --git a/linux-user/syscall.c b/linux-user/syscall.c
> index 9bf901fa11..6c1f28a1f7 100644
> --- a/linux-user/syscall.c
> +++ b/linux-user/syscall.c
> @@ -7496,26 +7496,35 @@ static int open_self_auxv(void *cpu_env, int fd)
>
>  static int is_proc_myself(const char *filename, const char *entry)
>  {
> -    if (!strncmp(filename, "/proc/", strlen("/proc/"))) {
> -        filename += strlen("/proc/");
> -        if (!strncmp(filename, "self/", strlen("self/"))) {
> -            filename += strlen("self/");
> -        } else if (*filename >= '1' && *filename <= '9') {
> -            char myself[80];
> -            snprintf(myself, sizeof(myself), "%d/", getpid());
> -            if (!strncmp(filename, myself, strlen(myself))) {
> -                filename += strlen(myself);
> -            } else {
> -                return 0;
> -            }
> -        } else {
> -            return 0;
> -        }
> -        if (!strcmp(filename, entry)) {
> -            return 1;
> -        }
> +    char proc_self_entry[PATH_MAX + 1];
> +    char proc_self_entry_realpath[PATH_MAX + 1];
> +    char filename_realpath[PATH_MAX + 1];
> +
> +    if (PATH_MAX < snprintf(proc_self_entry,
> +                            sizeof(proc_self_entry),
> +                            "/proc/self/%s",
> +                            entry)) {
> +        /* Full path to "entry" is too long to fit in the buffer */
> +        return 0;
>      }
> -    return 0;
> +
> +    if (!realpath(filename, filename_realpath)) {
> +        /* File does not exist, or can't be canonicalized */
> +        return 0;
> +    }
> +
> +    if (!realpath(proc_self_entry, proc_self_entry_realpath)) {
> +        /* Procfs entry does not exist */
> +        return 0;
> +    }
> +
> +    if (strcmp(filename_realpath, proc_self_entry_realpath) != 0) {
> +        /* Paths are different */
> +        return 0;
> +    }
> +
> +    /* filename refers to /proc/self/<entry> */
> +    return 1;
>  }
>
>  #if defined(HOST_WORDS_BIGENDIAN) != defined(TARGET_WORDS_BIGENDIAN)
> --
> 2.14.3
>
>