tftpd: fix download: we must change user AFTER bind

tftp_protocol                                       1466    1468      +2

1 files changed, 42 insertions, 37 deletions

diff --git a/networking/tftp.c b/networking/tftp.c
index 5fac48769..bea215c01 100644
--- a/networking/tftp.c
+++ b/networking/tftp.c
@@ -83,9 +83,7 @@ enum {
 struct globals {
         /* u16 TFTP_ERROR; u16 reason; both network-endian, then error text: */
         uint8_t error_pkt[4 + 32];
-#if ENABLE_TFTPD
         char *user_opt;
-#endif
         /* used in tftpd_main(), a bit big for stack: */
         char block_buf[TFTP_BLKSIZE_DEFAULT];
 };
@@ -183,7 +181,7 @@ static int tftp_protocol(
         int open_mode, local_fd;
         int retries, waittime_ms;
         int io_bufsize = blksize + 4;
-        char *cp;
+        char *cp = cp; /* for compiler */
         /* Can't use RESERVE_CONFIG_BUFFER here since the allocation
          * size varies meaning BUFFERS_GO_ON_STACK would fail */
         /* We must keep the transmit and receive buffers seperate */
@@ -194,40 +192,8 @@ static int tftp_protocol(
         socket_fd = xsocket(peer_lsa->u.sa.sa_family, SOCK_DGRAM, 0);
         setsockopt_reuseaddr(socket_fd);
 
-#if ENABLE_TFTPD
-        if (user_opt) {
-                struct passwd *pw = getpwnam(user_opt); /* initgroups, setgid, setuid */
-                if (!pw)
-                        bb_error_msg_and_die("unknown user '%s'", user_opt);
-                change_identity(pw);
-        }
-#endif
-
-        if (CMD_PUT(option_mask32)) {
-                open_mode = O_RDONLY;
-        } else {
-                open_mode = O_WRONLY | O_TRUNC | O_CREAT;
-#if ENABLE_TFTPD
-                if ((option_mask32 & (TFTPD_OPT+TFTPD_OPT_c)) == TFTPD_OPT) {
-                        /* tftpd without -c */
-                        open_mode = O_WRONLY | O_TRUNC;
-                }
-#endif
-        }
-        if (!(option_mask32 & TFTPD_OPT)) {
-                local_fd = CMD_GET(option_mask32) ? STDOUT_FILENO : STDIN_FILENO;
-                if (NOT_LONE_DASH(local_file))
-                        local_fd = xopen(local_file, open_mode);
-        } else {
-                local_fd = open_or_warn(local_file, open_mode);
-                if (local_fd < 0) {
-                        /*error_pkt_reason = ERR_NOFILE/ERR_ACCESS?*/
-                        strcpy(error_pkt_str, "can't open file");
-                        goto send_err_pkt;
-                }
-        }
-
         block_nr = 1;
+
         if (!ENABLE_TFTP || our_lsa) {
                 /* tftpd */
 
@@ -258,9 +224,48 @@ static int tftp_protocol(
                          * that is, for "block 0" which is our OACK pkt */
                         opcode = TFTP_OACK;
                         cp = xbuf + 2;
+                        /* to be continued, see below */
+                }
+#endif
+                if (user_opt) {
+                        struct passwd *pw = getpwnam(user_opt);
+                        if (!pw)
+                                bb_error_msg_and_die("unknown user '%s'", user_opt);
+                        change_identity(pw); /* initgroups, setgid, setuid */
+                }
+        }
+
+        /* Open local file (must be after changing user) */
+        if (CMD_PUT(option_mask32)) {
+                open_mode = O_RDONLY;
+        } else {
+                open_mode = O_WRONLY | O_TRUNC | O_CREAT;
+#if ENABLE_TFTPD
+                if ((option_mask32 & (TFTPD_OPT+TFTPD_OPT_c)) == TFTPD_OPT) {
+                        /* tftpd without -c */
+                        open_mode = O_WRONLY | O_TRUNC;
+                }
+#endif
+        }
+        if (!(option_mask32 & TFTPD_OPT)) {
+                local_fd = CMD_GET(option_mask32) ? STDOUT_FILENO : STDIN_FILENO;
+                if (NOT_LONE_DASH(local_file))
+                        local_fd = xopen(local_file, open_mode);
+        } else {
+                local_fd = open_or_warn(local_file, open_mode);
+                if (local_fd < 0) {
+                        /*error_pkt_reason = ERR_NOFILE/ERR_ACCESS?*/
+                        strcpy(error_pkt_str, "can't open file");
+                        goto send_err_pkt;
+                }
+        }
+
+        if (!ENABLE_TFTP || our_lsa) {
+#if ENABLE_FEATURE_TFTP_BLOCKSIZE
+                if (blksize != TFTP_BLKSIZE_DEFAULT) {
+                        /* Create and send OACK packet. continued */
                         goto add_blksize_opt;
                 }
-                /* else: just fall into while (1) loop below */
 #endif
         } else {
                 /* tftp */