tftpd: make open() check r/w permissions instead of doing it ourself.

Add -r "prohibit upload" opt for those lazy people who run tftpd as root.
-40 bytes.

1 files changed, 27 insertions, 21 deletions

diff --git a/networking/tftp.c b/networking/tftp.c
index 25001c22c..3075ab04b 100644
--- a/networking/tftp.c
+++ b/networking/tftp.c
@@ -56,6 +56,8 @@
  * CMD_GET(cmd) and CMD_PUT(cmd) are mutually exclusive
  */
 
+// TODO: emit error packets before dying
+
 
 #if ENABLE_FEATURE_TFTP_BLOCKSIZE
 
@@ -340,7 +342,7 @@ static int tftp_protocol(
 
                         const char *msg = "";
 
-                        if (rbuf[4] != '\0') {
+                        if (len > 4 && rbuf[4] != '\0') {
                                 msg = &rbuf[4];
                                 rbuf[tftp_bufsize - 1] = '\0';
                         } else if (recv_blk < ARRAY_SIZE(errcode_str)) {
@@ -533,14 +535,14 @@ static len_and_sockaddr *get_sock_lsa(int s)
 }
 
 int tftpd_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
-int tftpd_main(int argc ATTRIBUTE_UNUSED, char **argv ATTRIBUTE_UNUSED)
+int tftpd_main(int argc ATTRIBUTE_UNUSED, char **argv)
 {
-        struct stat statbuf;
         char block_buf[TFTP_BLOCKSIZE_DEFAULT];
         len_and_sockaddr *our_lsa;
         len_and_sockaddr *peer_lsa;
         char *filename, *mode, *opt_str;
-        int result, opcode, cmd, req_modebits, open_mode, local_fd, blksize;
+        int opt_r, result, opcode, open_mode, local_fd, blksize;
+        USE_GETPUT(int cmd;)
 
         our_lsa = get_sock_lsa(STDIN_FILENO);
         if (!our_lsa)
@@ -548,8 +550,10 @@ int tftpd_main(int argc ATTRIBUTE_UNUSED, char **argv ATTRIBUTE_UNUSED)
         peer_lsa = xzalloc(LSA_LEN_SIZE + our_lsa->len);
         peer_lsa->len = our_lsa->len;
 
-        if (argv[1])
-                xchdir(argv[1]);
+        opt_r = getopt32(argv, "r");
+        argv += optind;
+        if (argv[0])
+                xchdir(argv[0]);
 
         result = recv_from_to(STDIN_FILENO, block_buf, sizeof(block_buf),
                         0 /* flags */,
@@ -558,7 +562,10 @@ int tftpd_main(int argc ATTRIBUTE_UNUSED, char **argv ATTRIBUTE_UNUSED)
         opcode = ntohs(*(uint16_t*)block_buf);
         if (result < 4 || result >= sizeof(block_buf)
          || block_buf[result-1] != '\0'
-         || (opcode != TFTP_RRQ && opcode != TFTP_WRQ)
+         || (USE_FEATURE_TFTP_GET(opcode != TFTP_RRQ) /* not download */
+             USE_GETPUT(&&)
+             USE_FEATURE_TFTP_GET(opcode != TFTP_WRQ) /* not upload */
+            )
         ) {
                 bb_error_msg_and_die("malformed packet");
         }
@@ -584,21 +591,20 @@ int tftpd_main(int argc ATTRIBUTE_UNUSED, char **argv ATTRIBUTE_UNUSED)
                 }
         }
 #endif
-        xstat(filename, &statbuf);
-        /* if opcode == TFTP_WRQ: */
-        cmd = 1; /* CMD_GET: we will receive file's data */
-        req_modebits = 0222; /* writable by anyone */
-        open_mode = O_WRONLY | O_TRUNC;
-        if (opcode == TFTP_RRQ) {
-                cmd = 2; /* CMD_PUT */
-                req_modebits = 0444; /* readable by anyone */
-                open_mode = O_RDONLY;
-        }
-        if (!S_ISREG(statbuf.st_mode)
-         || (statbuf.st_mode & req_modebits) != req_modebits
-        ) {
-                bb_error_msg_and_die("access to '%s' is denied", filename);
+
+#if ENABLE_FEATURE_TFTP_PUT
+        /* in case opcode is TFTP_RRQ: */
+        USE_GETPUT(cmd = 2;) /* CMD_PUT: we will send file's data */
+        open_mode = O_RDONLY;
+#endif
+#if ENABLE_FEATURE_TFTP_GET
+        if (!ENABLE_FEATURE_TFTP_PUT || opcode == TFTP_WRQ) {
+                if (opt_r)
+                        bb_error_msg_and_die("upload is prohibited");
+                USE_GETPUT(cmd = 1;) /* CMD_GET: we will receive file's data */
+                open_mode = O_WRONLY | O_TRUNC;
         }
+#endif
         local_fd = xopen(filename, open_mode);
 
         close(STDIN_FILENO); /* close old, possibly wildcard socket */