1 files changed, 51 insertions, 1 deletions

diff --git a/misc.c b/misc.c
index a7a23dcc6..ddff00e52 100644
--- a/misc.c
+++ b/misc.c
@@ -48,8 +48,9 @@
 #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
@@ -642,6 +643,55 @@ 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 & 002) != 0)
+                return 0;
+        if ((st->st_mode & 020) != 0) {
+                /* If the file is group-writable, the group in question must
+                 * have exactly one member, namely the file's owner.
+                 * (Zero-member groups are typically used by setgid
+                 * binaries, and are unlikely to be suitable.)
+                 */
+                struct passwd *pw;
+                struct group *gr;
+                int members = 0;
+
+                gr = getgrgid(st->st_gid);
+                if (!gr)
+                        return 0;
+
+                /* Check primary group memberships. */
+                while ((pw = getpwent()) != NULL) {
+                        if (pw->pw_gid == gr->gr_gid) {
+                                ++members;
+                                if (pw->pw_uid != uid)
+                                        return 0;
+                        }
+                }
+                endpwent();
+
+                pw = getpwuid(st->st_uid);
+                if (!pw)
+                        return 0;
+
+                /* Check supplementary group memberships. */
+                if (gr->gr_mem[0]) {
+                        ++members;
+                        if (strcmp(pw->pw_name, gr->gr_mem[0]) ||
+                            gr->gr_mem[1])
+                                return 0;
+                }
+
+                if (!members)
+                        return 0;
+        }
+        return 1;
+}
+
+int
 tun_open(int tun, int mode)
 {
 #if defined(CUSTOM_SYS_TUN_OPEN)