lib: Limit space and time used by 'qemu-img info' subprocess.

After fuzzing 'qemu-img info' I found that certain files can cause the
command to use lots of memory and time.  Modify the command
mini-library to allow us to place resource limits on subprocesses, and
use these to limit the amount of space and time used by 'qemu-img info'.

configure.ac

@@ -305,8 +305,10 @@ AC_CHECK_HEADERS([\
     linux/raid/md_u.h \
     printf.h \
     sys/inotify.h \
+    sys/resource.h \
     sys/socket.h \
     sys/statvfs.h \
+    sys/time.h \
     sys/types.h \
     sys/un.h \
     sys/wait.h \
@@ -335,6 +337,7 @@ AC_CHECK_FUNCS([\
     posix_fadvise \
     removexattr \
     setitimer \
+    setrlimit \
     setxattr \
     sigaction \
     statvfs \

src/command.c

@@ -77,6 +77,13 @@
 #include <sys/wait.h>
 #include <sys/select.h>
 
+#ifdef HAVE_SYS_TIME_H
+#include <sys/time.h>
+#endif
+#ifdef HAVE_SYS_RESOURCE_H
+#include <sys/resource.h>
+#endif
+
 #include "guestfs.h"
 #include "guestfs-internal.h"
 
@@ -101,6 +108,12 @@ struct buffering {
   void (*close_data) (struct command *cmd);
 };
 
+struct child_rlimits {
+  struct child_rlimits *next;
+  int resource;
+  long limit;
+};
+
 struct command
 {
   guestfs_h *g;
@@ -139,6 +152,9 @@ struct command
   cmd_child_callback child_callback;
   void *child_callback_data;
 
+  /* Optional child limits. */
+  struct child_rlimits *child_rlimits;
+
   /* Optional stdin forwarding to the child. */
   int infd;
 };
@@ -329,6 +345,22 @@ guestfs_int_cmd_set_child_callback (struct command *cmd,
   cmd->child_callback_data = data;
 }
 
+/* Set up child rlimits, in case the process we are running could
+ * consume lots of space or time.
+ */
+void
+guestfs_int_cmd_set_child_rlimit (struct command *cmd, int resource, long limit)
+{
+  struct child_rlimits *p;
+
+  p = safe_malloc (cmd->g, sizeof *p);
+  p->resource = resource;
+  p->limit = limit;
+  p->next = cmd->child_rlimits;
+  cmd->child_rlimits = p;
+}
+
+
 /* Finish off the command by either NULL-terminating the argv array or
  * adding a terminating \0 to the string, or die with an internal
  * error if no command has been added.
@@ -390,6 +422,10 @@ run_command (struct command *cmd, bool get_stdin_fd, bool get_stdout_fd,
   int outfd[2] = { -1, -1 };
   int infd[2] = { -1, -1 };
   char status_string[80];
+#ifdef HAVE_SETRLIMIT
+  struct child_rlimits *child_rlimit;
+  struct rlimit rlimit;
+#endif
 
   get_stdout_fd = get_stdout_fd || cmd->stdout_callback != NULL;
   get_stderr_fd = get_stderr_fd || cmd->capture_errors;
@@ -510,6 +546,23 @@ run_command (struct command *cmd, bool get_stdin_fd, bool get_stdout_fd,
       _exit (EXIT_FAILURE);
   }
 
+#ifdef HAVE_SETRLIMIT
+  for (child_rlimit = cmd->child_rlimits;
+       child_rlimit != NULL;
+       child_rlimit = child_rlimit->next) {
+    rlimit.rlim_cur = rlimit.rlim_max = child_rlimit->limit;
+    if (setrlimit (child_rlimit->resource, &rlimit) == -1) {
+      /* EPERM means we're trying to raise the limit (ie. the limit is
+       * already more restrictive than what we want), so ignore it.
+       */
+      if (errno != EPERM) {
+        perror ("setrlimit");
+        _exit (EXIT_FAILURE);
+      }
+    }
+  }
+#endif /* HAVE_SETRLIMIT */
+
   /* Run the command. */
   switch (cmd->style) {
   case COMMAND_STYLE_EXECV:

src/guestfs-internal.h

@@ -864,6 +864,7 @@ extern void guestfs_int_cmd_set_stdout_callback (struct command *, cmd_stdout_ca
 #define CMD_STDOUT_FLAG_UNBUFFERED      1
 #define CMD_STDOUT_FLAG_WHOLE_BUFFER    2
 extern void guestfs_int_cmd_set_stderr_to_stdout (struct command *);
+extern void guestfs_int_cmd_set_child_rlimit (struct command *, int resource, long limit);
 extern void guestfs_int_cmd_clear_capture_errors (struct command *);
 extern void guestfs_int_cmd_clear_close_files (struct command *);
 extern void guestfs_int_cmd_set_child_callback (struct command *, cmd_child_callback child_callback, void *data);

src/info.c

@@ -31,6 +31,14 @@
 #include <assert.h>
 #include <string.h>
 
+#ifdef HAVE_SYS_TIME_H
+#include <sys/time.h>
+#endif
+
+#ifdef HAVE_SYS_RESOURCE_H
+#include <sys/resource.h>
+#endif
+
 #if HAVE_YAJL
 #include <yajl/yajl_tree.h>
 #endif
@@ -269,7 +277,13 @@ get_json_output (guestfs_h *g, const char *filename)
   guestfs_int_cmd_add_arg (cmd, "json");
   guestfs_int_cmd_add_arg (cmd, fdpath);
   guestfs_int_cmd_set_stdout_callback (cmd, parse_json, &tree,
-                                     CMD_STDOUT_FLAG_WHOLE_BUFFER);
+                                       CMD_STDOUT_FLAG_WHOLE_BUFFER);
+#ifdef RLIMIT_AS
+  guestfs_int_cmd_set_child_rlimit (cmd, RLIMIT_AS, 1000000000 /* 1GB */);
+#endif
+#ifdef RLIMIT_CPU
+  guestfs_int_cmd_set_child_rlimit (cmd, RLIMIT_CPU, 10 /* seconds */);
+#endif
   r = guestfs_int_cmd_run (cmd);
   close (fd);
   if (r == -1)
@@ -548,6 +562,12 @@ old_parser_run_qemu_img_info (guestfs_h *g, const char *filename,
   guestfs_int_cmd_add_arg (cmd, "info");
   guestfs_int_cmd_add_arg (cmd, safe_filename);
   guestfs_int_cmd_set_stdout_callback (cmd, fn, data, 0);
+#ifdef RLIMIT_AS
+  guestfs_int_cmd_set_child_rlimit (cmd, RLIMIT_AS, 1000000000 /* 1GB */);
+#endif
+#ifdef RLIMIT_CPU
+  guestfs_int_cmd_set_child_rlimit (cmd, RLIMIT_CPU, 10 /* seconds */);
+#endif
   r = guestfs_int_cmd_run (cmd);
   if (r == -1)
     return -1;