Re: [Qemu-devel] [PATCH] linux-user: identify running binary in /proc/$$/exe

[Peter Maydell <peter.maydell@linaro.org>]

On 11 March 2013 17:19, Andreas Schwab <schwab@suse.de> wrote:
> Some applications like to test /proc/$$/exe (where $$ is the own pid) to
> find out who they are.  Handle it like /proc/self/exe.
>
> Also, do the same handling in readlinkat.

Sorry I didn't get round to reviewing this earlier; I think
it slipped through the cracks :-(

> diff --git a/linux-user/syscall.c b/linux-user/syscall.c
> index 19630ea..3e5a6ae 100644
> --- a/linux-user/syscall.c
> +++ b/linux-user/syscall.c
> @@ -6413,7 +6413,10 @@ abi_long do_syscall(void *cpu_env, int num, abi_long arg1,
>              if (!p || !p2)
>                  ret = -TARGET_EFAULT;
>              else {
> -                if (strncmp((const char *)p, "/proc/self/exe", 14) == 0) {
> +                char myself[PATH_MAX];
> +                snprintf(myself, sizeof(myself), "/proc/%d/exe", getpid());
> +                if (strncmp((const char *)p, "/proc/self/exe", 14) == 0 ||
> +                    strcmp((const char *)p, myself) == 0) {
>                      char real[PATH_MAX];
>                      temp = realpath(exec_path,real);
>                      ret = (temp==NULL) ? get_errno(-1) : strlen(real) ;
> @@ -6429,13 +6432,24 @@ abi_long do_syscall(void *cpu_env, int num, abi_long arg1,
>  #if defined(TARGET_NR_readlinkat) && defined(__NR_readlinkat)
>      case TARGET_NR_readlinkat:
>          {
> -            void *p2;
> +            void *p2, *temp;
>              p  = lock_user_string(arg2);
>              p2 = lock_user(VERIFY_WRITE, arg3, arg4, 0);
>              if (!p || !p2)
>                 ret = -TARGET_EFAULT;
> -            else
> -                ret = get_errno(sys_readlinkat(arg1, path(p), p2, arg4));

You could add braces on the 'then' part of this if() and get rid
of the stray hardcoded tab in the existing code. (not a requirement
but since we're in the area anyway...)

> +            else {
> +                char myself[PATH_MAX];
> +                snprintf(myself, sizeof(myself), "/proc/%d/exe", getpid());
> +                if (strncmp((const char *)p, "/proc/self/exe", 14) == 0 ||
> +                    strcmp((const char *)p, myself) == 0) {
> +                    char real[PATH_MAX];
> +                    temp = realpath(exec_path,real);
> +                    ret = (temp==NULL) ? get_errno(-1) : strlen(real) ;
> +                    snprintf((char *)p2, arg3, "%s", real);

This seems to be a fair chunk of code in common with the readlink
case above -- can we abstract it out? (ideally to a function
somewhere in the same area of this file as the code that handles
intercepting /proc/ calls for open().)

It would be consistent to support /proc/$$/ for all the open()
intercepts too.

> +                }
> +                else
> +                    ret = get_errno(sys_readlinkat(arg1, path(p), p2, arg4));
> +            }
>              unlock_user(p2, arg3, ret);
>              unlock_user(p, arg2, 0);
>          }
> --
> 1.8.1.5

thanks
-- PMM