[Qemu-devel] [PATCH v2 2/2] Allow -runas to be specified as UID:GID as well as USERNAME

[Chris Webb]

This allows qemu to drop privileges to a dynamically allocated, anonymous UID
and GID without needing a temporary /etc/passwd entry for that UID. The
UID:GID format is very standard, being (for example) the syntax used by
chown(1) for numeric IDs.

Signed-off-by: Chris Webb <address@hidden>
---
 os-posix.c |   16 +++++++++++++++-
 1 files changed, 15 insertions(+), 1 deletions(-)

diff --git a/os-posix.c b/os-posix.c
index 1b2061a..44a841b 100644
--- a/os-posix.c
+++ b/os-posix.c
@@ -179,6 +179,15 @@ void os_parse_cmd_args(int index, const char *optarg)
     case QEMU_OPTION_runas:
         user_pwd = getpwnam(optarg);
         if (!user_pwd) {
+            long uid, gid, tail;
+            if (sscanf(optarg, "%ld:%ld%ln", &uid, &gid, &tail) >= 2
+                  && !optarg[tail]) {
+                user_pwd = g_new0(struct passwd, 1);
+                user_pwd->pw_uid = uid;
+                user_pwd->pw_gid = gid;
+            }
+        }
+        if (!user_pwd) {
             fprintf(stderr, "User \"%s\" doesn't exist\n", optarg);
             exit(1);
         }
@@ -200,7 +209,12 @@ static void change_process_uid(void)
             fprintf(stderr, "Failed to setgid(%d)\n", user_pwd->pw_gid);
             exit(1);
         }
-        if (initgroups(user_pwd->pw_name, user_pwd->pw_gid) < 0) {
+        if (!user_pwd->pw_name) {
+            if (setgroups(0, NULL) < 0) {
+                fprintf(stderr, "Failed to setgroups(0, NULL)\n");
+                exit(1);
+            }
+        } else if (initgroups(user_pwd->pw_name, user_pwd->pw_gid) < 0) {
             fprintf(stderr, "Failed to initgroups(\"%s\", %d)\n",
                     user_pwd->pw_name, user_pwd->pw_gid);
             exit(1);
-- 
1.7.5.4