1 files changed, 26 insertions, 1 deletions

diff --git a/misc.c b/misc.c
index e1f723123..4ca318423 100644
--- a/misc.c
+++ b/misc.c
@@ -45,8 +45,9 @@
 #include <netdb.h>
 #ifdef HAVE_PATHS_H
 # include <paths.h>
-#include <pwd.h>
 #endif
+#include <pwd.h>
+#include <grp.h>
 #ifdef SSH_TUN_OPENBSD
 #include <net/if.h>
 #endif
@@ -638,6 +639,30 @@ read_keyfile_line(FILE *f, const char *filename, char *buf, size_t bufsz,
 }
 
 int
+secure_permissions(struct stat *st, uid_t uid)
+{
+        if (st->st_uid != 0 && st->st_uid != uid)
+                return 0;
+        if ((st->st_mode & 020) != 0) {
+                /* If the file is group-writable, the group in question must
+                 * have at most one member, namely the file's owner.
+                 */
+                struct passwd *pw = getpwuid(st->st_uid);
+                struct group *gr = getgrgid(st->st_gid);
+                if (!pw || !gr)
+                        return 0;
+                else if (gr->gr_mem[0]) {
+                        if (strcmp(pw->pw_name, gr->gr_mem[0]) ||
+                            gr->gr_mem[1])
+                                return 0;
+                }
+        }
+        if ((st->st_mode & 002) != 0)
+                return 0;
+        return 1;
+}
+
+int
 tun_open(int tun, int mode)
 {
 #if defined(CUSTOM_SYS_TUN_OPEN)