Re: [Qemu-devel] [PATCH] linux-user: hijack open() for thread directories

[Shu-Chun Weng]

Ping. Any comments on this? Patchwork:
http://patchwork.ozlabs.org/patch/1151167/

On Wed, Aug 21, 2019 at 1:19 PM Shu-Chun Weng <address@hidden> wrote:

> Besides /proc/self|<pid>, files under /proc/thread-self and
> /proc/self|<pid>/task/<tid> also expose host information to the guest
> program. This patch adds them to the hijack infrastracture. Note that
> is_proc_myself() does not check if the <tid> matches the current thread
> and is thus only suitable for procfs files that are identical for all
> threads in the same process.
>
> Behavior verified with guest program:
>
> long main_thread_tid;
>
> long gettid() {
>   return syscall(SYS_gettid);
> }
>
> void print_info(const char* cxt, const char* dir) {
>   char buf[1024];
>   FILE* fp;
>
>   snprintf(buf, sizeof(buf), "%s/cmdline", dir);
>   fp = fopen(buf, "r");
>
>   if (fp == NULL) {
>     printf("%s: can't open %s\n", cxt, buf);
>   } else {
>     fgets(buf, sizeof(buf), fp);
>     printf("%s %s cmd: %s\n", cxt, dir, buf);
>     fclose(fp);
>   }
>
>   snprintf(buf, sizeof(buf), "%s/maps", dir);
>   fp = fopen(buf, "r");
>
>   if (fp == NULL) {
>     printf("%s: can't open %s\n", cxt, buf);
>   } else {
>     char seen[128][128];
>     int n = 0, is_new = 0;
>     while(fgets(buf, sizeof(buf), fp) != NULL) {
>       const char* p = strrchr(buf, ' ');
>       if (p == NULL || *(p + 1) == '\n') {
>         continue;
>       }
>       ++p;
>       is_new = 1;
>       for (int i = 0; i < n; ++i) {
>         if (strncmp(p, seen[i], sizeof(seen[i])) == 0) {
>           is_new = 0;
>           break;
>         }
>       }
>       if (is_new) {
>         printf("%s %s map: %s", cxt, dir, p);
>         if (n < 128) {
>           strncpy(seen[n], p, sizeof(seen[n]));
>           seen[n][sizeof(seen[n]) - 1] = '\0';
>           ++n;
>         }
>       }
>     }
>     fclose(fp);
>   }
> }
>
> void* thread_main(void* _) {
>   char buf[1024];
>
>   print_info("Child", "/proc/thread-self");
>
>   snprintf(buf, sizeof(buf), "/proc/%ld/task/%ld", (long) getpid(),
> main_thread_tid);
>   print_info("Child", buf);
>
>   snprintf(buf, sizeof(buf), "/proc/%ld/task/%ld", (long) getpid(), (long)
> gettid());
>   print_info("Child", buf);
>
>   return NULL;
> }
>
> int main() {
>   char buf[1024];
>   pthread_t thread;
>   int ret;
>
>   print_info("Main", "/proc/thread-self");
>   print_info("Main", "/proc/self");
>
>   snprintf(buf, sizeof(buf), "/proc/%ld", (long) getpid());
>   print_info("Main", buf);
>
>   main_thread_tid = gettid();
>   snprintf(buf, sizeof(buf), "/proc/self/task/%ld", main_thread_tid);
>   print_info("Main", buf);
>
>   snprintf(buf, sizeof(buf), "/proc/%ld/task/%ld", (long) getpid(),
> main_thread_tid);
>   print_info("Main", buf);
>
>   if ((ret = pthread_create(&thread, NULL, &thread_main, NULL)) < 0) {
>     printf("ptherad_create failed: %s (%d)\n", strerror(ret), ret);
>   }
>
>   pthread_join(thread, NULL);
>   return 0;
> }
>
> Signed-off-by: Shu-Chun Weng <address@hidden>
> ---
>  linux-user/syscall.c | 40 ++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 40 insertions(+)
>
> diff --git a/linux-user/syscall.c b/linux-user/syscall.c
> index 8367cb138d..73fe82bcc7 100644
> --- a/linux-user/syscall.c
> +++ b/linux-user/syscall.c
> @@ -6968,17 +6968,57 @@ static int open_self_auxv(void *cpu_env, int fd)
>      return 0;
>  }
>
> +static int consume_task_directories(const char **filename)
> +{
> +    if (!strncmp(*filename, "task/", strlen("task/"))) {
> +        *filename += strlen("task/");
> +        if (**filename < '1' || **filename > '9') {
> +            return 0;
> +        }
> +        /*
> +         * Don't care about the exact tid.
> +         * XXX: this allows opening files under /proc/self|<pid>/task/<n>
> where
> +         *      <n> is not a valid thread id. Consider checking if the
> file
> +         *      actually exists.
> +         */
> +        const char *p = *filename + 1;
> +        while (*p >= '0' && *p <= '9') {
> +            ++p;
> +        }
> +        if (*p == '/') {
> +            *filename = p + 1;
> +            return 1;
> +        } else {
> +            return 0;
> +        }
> +    }
> +    return 1;
> +}
> +
> +/*
> + * Determines if filename refer to a procfs file for the current process
> or any
> + * thread within the current process. This function should only be used
> to check
> + * for files that have identical contents in all threads, e.g. exec,
> maps, etc.
> + */
>  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/");
> +            if (!consume_task_directories(&filename)) {
> +                return 0;
> +            }
> +        } else if (!strncmp(filename, "thread-self/",
> strlen("thread-self/"))) {
> +            filename += strlen("thread-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);
> +                if (!consume_task_directories(&filename)) {
> +                    return 0;
> +                }
>              } else {
>                  return 0;
>              }
> --
> 2.23.0.rc1.153.gdeed80330f-goog
>
>

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