ftpd: make DIR parameter work for non-root too: chdir to it instead of chroot

Unfortunately, chroot() works only for root user, because of attacks
on setuid binaries (make DIR/lib/ld-linux.so a shell, hardlink to
a setuid binary, chroot to DIR, execute it and get root shell).

function                                             old     new   delta
ftpd_main                                           2160    2180     +20

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 16 insertions, 1 deletions

diff --git a/networking/ftpd.c b/networking/ftpd.c
index 7735b7233..8345ae67c 100644
--- a/networking/ftpd.c
+++ b/networking/ftpd.c
@@ -1223,11 +1223,26 @@ int ftpd_main(int argc UNUSED_PARAM, char **argv)
 #endif
         argv += optind;
         if (argv[0]) {
+                const char *basedir = argv[0];
 #if !BB_MMU
                 G.root_fd = xopen("/", O_RDONLY | O_DIRECTORY);
                 close_on_exec_on(G.root_fd);
 #endif
-                xchroot(argv[0]);
+                if (chroot(basedir) == 0)
+                        basedir = "/";
+#if !BB_MMU
+                else {
+                        close(G.root_fd);
+                        G.root_fd = -1;
+                }
+#endif
+                /*
+                 * If chroot failed, assume that we aren't root,
+                 * and at least chdir to the specified DIR
+                 * (older versions were dying with error message).
+                 * If chroot worked, move current dir to new "/":
+                 */
+                xchdir(basedir);
         }
 
 #if ENABLE_FEATURE_FTP_AUTHENTICATION