Move sys_reset_uid_gid to library

This fixes a problem where ‘gcc -fanalyzer -flto’ (GCC 10)
complained that sys_reset_uid_gid was defined but not used in some
modules.  This function belonged in a .c file anyway.
* lib/rtapelib.c (sys_reset_uid_gid):
* paxlib/rtape.c (sys_reset_uid_gid):
Move here from system.h.  The code is now duplicated, but so is
most of the rest of this file anyway.
* lib/system.h (sys_reset_uid_gid): Remove.

1 files changed, 23 insertions, 0 deletions

diff --git a/paxlib/rtape.c b/paxlib/rtape.c
index 2364594..1089d92 100644
--- a/paxlib/rtape.c
+++ b/paxlib/rtape.c
@@ -358,6 +358,29 @@ encode_oflag (char *buf, int oflag)
     strcat (buf, "|O_TRUNC");
 }
 
+/* Reset user and group IDs to be those of the real user.
+   Return NULL on success, a failing syscall name (setting errno) on error.  */
+static char const *
+sys_reset_uid_gid (void)
+{
+#if !MSDOS
+  uid_t uid = getuid ();
+  gid_t gid = getgid ();
+  struct passwd *pw = getpwuid (uid);
+
+  if (!pw)
+    return "getpwuid";
+  if (initgroups (pw->pw_name, gid) != 0)
+    return "initgroups";
+  if (gid != getegid () && setgid (gid) != 0 && errno != EPERM)
+    return "setgid";
+  if (uid != geteuid () && setuid (uid) != 0 && errno != EPERM)
+    return "setuid";
+#endif
+
+  return NULL;
+}
+
 /* Open a remote file on the system specified in FILE_NAME, as the given user.
    FILE_NAME has the form `[USER@]HOST:FILE'.
    OPEN_MODE is O_RDONLY, O_WRONLY, etc.  If successful, return the