tftpd: options -c (allow _new_ files to be uploaded) and -u USER

function                                             old     new   delta
tftp_protocol                                       1316    1466    +150
packed_usage                                       23774   23798     +24
tftpd_main                                           509     502      -7
tftp_main                                            311     252     -59
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 2/2 up/down: 174/-66)           Total: 108 bytes
   text    data     bss     dec     hex filename
 797700     641    7380  805721   c4b59 busybox_old
 797833     641    7380  805854   c4bde busybox_unstripped

2 files changed, 88 insertions, 65 deletions

diff --git a/include/usage.h b/include/usage.h
index 7fe9ad063..ad9009763 100644
--- a/include/usage.h
+++ b/include/usage.h
@@ -3977,11 +3977,13 @@
         )
 
 #define tftpd_trivial_usage \
-       "[-r] [DIR]"
+       "[-cr] [-u USER] [DIR]"
 #define tftpd_full_usage \
-       "Transfer a file on request from a tftp client.\n" \
+       "Transfer a file on tftp client's request.\n" \
      "\nOptions:" \
      "\n        -r      Prohibit upload" \
+     "\n        -c      Allow file creation via upload" \
+     "\n        -u      Access files as USER" \
 
 #define time_trivial_usage \
        "[OPTION]... COMMAND [ARGS...]"
diff --git a/networking/tftp.c b/networking/tftp.c
index e0f2b91cf..5fac48769 100644
--- a/networking/tftp.c
+++ b/networking/tftp.c
@@ -51,6 +51,17 @@
 #define ERR_BAD_USER 7
 #define ERR_BAD_OPT  8
 
+/* masks coming from getopt32 */
+enum {
+        TFTP_OPT_GET = (1 << 0),
+        TFTP_OPT_PUT = (1 << 1),
+        /* pseudo option: if set, it's tftpd */
+        TFTPD_OPT = (1 << 7) * ENABLE_TFTPD,
+        TFTPD_OPT_r = (1 << 8) * ENABLE_TFTPD,
+        TFTPD_OPT_c = (1 << 9) * ENABLE_TFTPD,
+        TFTPD_OPT_u = (1 << 10) * ENABLE_TFTPD,
+};
+
 #if ENABLE_FEATURE_TFTP_GET && !ENABLE_FEATURE_TFTP_PUT
 #define USE_GETPUT(...)
 #define CMD_GET(cmd) 1
@@ -61,9 +72,8 @@
 #define CMD_PUT(cmd) 1
 #else
 #define USE_GETPUT(...) __VA_ARGS__
-/* masks coming from getopt32 */
-#define CMD_GET(cmd) ((cmd) & 1)
-#define CMD_PUT(cmd) ((cmd) & 2)
+#define CMD_GET(cmd) ((cmd) & TFTP_OPT_GET)
+#define CMD_PUT(cmd) ((cmd) & TFTP_OPT_PUT)
 #endif
 /* NB: in the code below
  * CMD_GET(cmd) and CMD_PUT(cmd) are mutually exclusive
@@ -73,11 +83,15 @@
 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];
 };
 #define G (*(struct globals*)&bb_common_bufsiz1)
 #define block_buf        (G.block_buf   )
+#define user_opt         (G.user_opt    )
 #define error_pkt        (G.error_pkt   )
 #define INIT_G() \
         do { \
@@ -148,11 +162,10 @@ static char *tftp_get_blksize(char *buf, int len)
 #endif
 
 static int tftp_protocol(
-                USE_GETPUT(int cmd,)
                 len_and_sockaddr *our_lsa,
                 len_and_sockaddr *peer_lsa,
+                const char *local_file,
                 USE_TFTP(const char *remote_file,)
-                int local_fd,
                 int blksize)
 {
 #if !ENABLE_TFTP
@@ -167,6 +180,7 @@ static int tftp_protocol(
         uint16_t opcode;
         uint16_t block_nr;
         uint16_t recv_blk;
+        int open_mode, local_fd;
         int retries, waittime_ms;
         int io_bufsize = blksize + 4;
         char *cp;
@@ -180,6 +194,39 @@ 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 */
@@ -197,7 +244,7 @@ static int tftp_protocol(
                 if (error_pkt_reason || error_pkt_str[0])
                         goto send_err_pkt;
 
-                if (CMD_GET(cmd)) {
+                if (CMD_GET(option_mask32)) {
                         /* it's upload - we must ACK 1st packet (with filename)
                          * as if it's "block 0" */
                         block_nr = 0;
@@ -231,7 +278,7 @@ static int tftp_protocol(
 
                 /* build opcode */
                 opcode = TFTP_WRQ;
-                if (CMD_GET(cmd)) {
+                if (CMD_GET(option_mask32)) {
                         opcode = TFTP_RRQ;
                 }
                 cp = xbuf + 2;
@@ -276,7 +323,7 @@ static int tftp_protocol(
                 cp += 2;
                 block_nr++;
                 opcode = TFTP_ACK;
-                if (CMD_PUT(cmd)) {
+                if (CMD_PUT(option_mask32)) {
                         opcode = TFTP_DATA;
                         len = full_read(local_fd, cp, blksize);
                         if (len < 0) {
@@ -420,7 +467,7 @@ static int tftp_protocol(
                 /* block_nr is already advanced to next block# we expect
                  * to get / block# we are about to send next time */
 
-                if (CMD_GET(cmd) && (opcode == TFTP_DATA)) {
+                if (CMD_GET(option_mask32) && (opcode == TFTP_DATA)) {
                         if (recv_blk == block_nr) {
                                 int sz = full_write(local_fd, &rbuf[4], len - 4);
                                 if (sz != len - 4) {
@@ -440,7 +487,7 @@ static int tftp_protocol(
                         }
                 }
 
-                if (CMD_PUT(cmd) && (opcode == TFTP_ACK)) {
+                if (CMD_PUT(option_mask32) && (opcode == TFTP_ACK)) {
                         /* did peer ACK our last DATA pkt? */
                         if (recv_blk == (uint16_t) (block_nr - 1)) {
                                 if (finished)
@@ -462,6 +509,7 @@ static int tftp_protocol(
         } /* end of "while (1)" */
  ret:
         if (ENABLE_FEATURE_CLEAN_UP) {
+                close(local_fd);
                 close(socket_fd);
                 free(xbuf);
                 free(rbuf);
@@ -487,13 +535,11 @@ int tftp_main(int argc ATTRIBUTE_UNUSED, char **argv)
         len_and_sockaddr *peer_lsa;
         const char *local_file = NULL;
         const char *remote_file = NULL;
-        int port;
-        USE_GETPUT(int cmd;)
-        int local_fd;
-        int flags = 0;
-        int result;
-        int blksize;
         const char *blksize_str = "512";
+        int blksize;
+        int result;
+        int port;
+        USE_GETPUT(int opt;)
 
         INIT_G();
 
@@ -501,17 +547,13 @@ int tftp_main(int argc ATTRIBUTE_UNUSED, char **argv)
         opt_complementary = "" USE_FEATURE_TFTP_GET("g:") USE_FEATURE_TFTP_PUT("p:")
                         USE_GETPUT("g--p:p--g:");
 
-        USE_GETPUT(cmd =) getopt32(argv,
+        USE_GETPUT(opt =) getopt32(argv,
                         USE_FEATURE_TFTP_GET("g") USE_FEATURE_TFTP_PUT("p")
                                 "l:r:" USE_FEATURE_TFTP_BLOCKSIZE("b:"),
                         &local_file, &remote_file
                         USE_FEATURE_TFTP_BLOCKSIZE(, &blksize_str));
         argv += optind;
 
-        flags = O_RDONLY;
-        if (CMD_GET(cmd))
-                flags = O_WRONLY | O_CREAT | O_TRUNC;
-
 #if ENABLE_FEATURE_TFTP_BLOCKSIZE
         /* Check if the blksize is valid:
          * RFC2348 says between 8 and 65464 */
@@ -530,11 +572,6 @@ int tftp_main(int argc ATTRIBUTE_UNUSED, char **argv)
         if (!remote_file || !argv[0])
                 bb_show_usage();
 
-        local_fd = CMD_GET(cmd) ? STDOUT_FILENO : STDIN_FILENO;
-        if (!LONE_DASH(local_file)) {
-                local_fd = xopen(local_file, flags);
-        }
-
         port = bb_lookup_port(argv[1], "udp", 69);
         peer_lsa = xhost2sockaddr(argv[0], port);
 
@@ -545,14 +582,11 @@ int tftp_main(int argc ATTRIBUTE_UNUSED, char **argv)
 #endif
 
         result = tftp_protocol(
-                        USE_GETPUT(cmd,)
-                        NULL /* our_lsa*/,
-                        peer_lsa,
-                        remote_file, local_fd, blksize);
+                        NULL /* our_lsa*/, peer_lsa,
+                        local_file, remote_file,
+                        blksize);
 
-        if (ENABLE_FEATURE_CLEAN_UP)
-                close(local_fd);
-        if (result != EXIT_SUCCESS && !LONE_DASH(local_file) && CMD_GET(cmd)) {
+        if (result != EXIT_SUCCESS && NOT_LONE_DASH(local_file) && CMD_GET(opt)) {
                 unlink(local_file);
         }
         return result;
@@ -581,9 +615,9 @@ int tftpd_main(int argc ATTRIBUTE_UNUSED, char **argv)
 {
         len_and_sockaddr *our_lsa;
         len_and_sockaddr *peer_lsa;
-        char *filename, *mode;
+        char *local_file, *mode;
         const char *error_msg;
-        int opt_r, result, opcode, open_mode;
+        int opt, result, opcode;
         int local_fd = local_fd; /* for compiler */
         int blksize = blksize;
         USE_GETPUT(int cmd = cmd;)
@@ -596,7 +630,8 @@ int tftpd_main(int argc ATTRIBUTE_UNUSED, char **argv)
         peer_lsa = xzalloc(LSA_LEN_SIZE + our_lsa->len);
         peer_lsa->len = our_lsa->len;
 
-        opt_r = getopt32(argv, "r");
+        /* Shifting to not collide with TFTP_OPTs */
+        opt = option_mask32 = TFTPD_OPT | (getopt32(argv, "rcu:", &user_opt) << 8);
         argv += optind;
         if (argv[0])
                 xchdir(argv[0]);
@@ -616,15 +651,13 @@ int tftpd_main(int argc ATTRIBUTE_UNUSED, char **argv)
         ) {
                 goto err;
         }
-        filename = block_buf + 2;
-        if (filename[0] == '.' || strstr(filename, "/.")) {
-                error_msg = "dot in filename";
+        local_file = block_buf + 2;
+        if (local_file[0] == '.' || strstr(local_file, "/.")) {
+                error_msg = "dot in local_file";
                 goto err;
         }
-        mode = filename + strlen(filename) + 1;
-        if (mode >= block_buf + result
-         || strcmp(mode, "octet") != 0
-        ) {
+        mode = local_file + strlen(local_file) + 1;
+        if (mode >= block_buf + result || strcmp(mode, "octet") != 0) {
                 goto err;
         }
         blksize = TFTP_BLKSIZE_DEFAULT;
@@ -647,29 +680,16 @@ int tftpd_main(int argc ATTRIBUTE_UNUSED, char **argv)
         }
 #endif
 
-#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) {
+                if (opt & TFTPD_OPT_r) {
                         /* This would mean "disk full" - not true */
                         /*error_pkt_reason = ERR_WRITE;*/
                         error_msg = bb_msg_write_error;
                         goto err;
                 }
-                USE_GETPUT(cmd = 1;) /* CMD_GET: we will receive file's data */
-                open_mode = O_WRONLY | O_TRUNC;
-        }
-#endif
-        local_fd = open(filename, open_mode);
-        if (local_fd < 0) {
-                /*error_pkt_reason = ERR_NOFILE/ERR_ACCESS?*/
-                error_msg = "can't open file";
- err:
-                strcpy(error_pkt_str, error_msg);
+                USE_GETPUT(option_mask32 |= TFTP_OPT_GET;) /* will receive file's data */
+        } else {
+                USE_GETPUT(option_mask32 |= TFTP_OPT_PUT;) /* will send file's data */
         }
 
         close(STDIN_FILENO); /* close old, possibly wildcard socket */
@@ -679,14 +699,15 @@ int tftpd_main(int argc ATTRIBUTE_UNUSED, char **argv)
          * tftp_protocol() just sends one error pkt and returns */
  do_proto:
         result = tftp_protocol(
-                USE_GETPUT(cmd,)
                 our_lsa, peer_lsa,
-                USE_TFTP(NULL /*remote_file*/,)
-                local_fd,
+                local_file, USE_TFTP(NULL /*remote_file*/,)
                 blksize
         );
 
         return result;
+ err:
+        strcpy(error_pkt_str, error_msg);
+        goto do_proto;
 }
 
 #endif /* ENABLE_TFTPD */