tftp: fix memory leak on too long filename

Fixes

$ valgrind --leak-check=full ~/install-curl-git/bin/curl tftp://localhost/aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaz

==9752== Memcheck, a memory error detector
==9752== Copyright (C) 2002-2015, and GNU GPL'd, by Julian Seward et al.
==9752== Using Valgrind-3.11.0 and LibVEX; rerun with -h for copyright info
==9752== Command: /home/even/install-curl-git/bin/curl tftp://localhost/aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaz
==9752==
curl: (71) TFTP file name too long

==9752==
==9752== HEAP SUMMARY:
==9752== 505 bytes in 1 blocks are definitely lost in loss record 11 of 11
==9752==    at 0x4C2DB8F: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==9752==    by 0x4E61CED: Curl_urldecode (in /home/even/install-curl-git/lib/libcurl.so.4.4.0)
==9752==    by 0x4E75868: tftp_state_machine (in /home/even/install-curl-git/lib/libcurl.so.4.4.0)
==9752==    by 0x4E761B6: tftp_do (in /home/even/install-curl-git/lib/libcurl.so.4.4.0)
==9752==    by 0x4E711B6: multi_runsingle (in /home/even/install-curl-git/lib/libcurl.so.4.4.0)
==9752==    by 0x4E71D00: curl_multi_perform (in /home/even/install-curl-git/lib/libcurl.so.4.4.0)
==9752==    by 0x4E6950D: curl_easy_perform (in /home/even/install-curl-git/lib/libcurl.so.4.4.0)
==9752==    by 0x40E0B7: operate_do (in /home/even/install-curl-git/bin/curl)
==9752==    by 0x40E849: operate (in /home/even/install-curl-git/bin/curl)
==9752==    by 0x402693: main (in /home/even/install-curl-git/bin/curl)

Fixes https://oss-fuzz.com/v2/testcase-detail/5232311106797568
Credit to OSS Fuzz

Closes #1808

3 files changed, 40 insertions, 1 deletions

diff --git a/lib/tftp.c b/lib/tftp.c
index f6f4bce5b..6477e64ed 100644
--- a/lib/tftp.c
+++ b/lib/tftp.c
@@ -493,6 +493,7 @@ static CURLcode tftp_send_first(tftp_state_data_t *state, tftp_event_t event)
 
     if(strlen(filename) > (state->blksize - strlen(mode) - 4)) {
       failf(data, "TFTP file name too long\n");
+      free(filename);
       return CURLE_TFTP_ILLEGAL; /* too long file name field */
     }
 
diff --git a/tests/data/Makefile.inc b/tests/data/Makefile.inc
index 575cf48cc..9da3e7e94 100644
--- a/tests/data/Makefile.inc
+++ b/tests/data/Makefile.inc
@@ -155,7 +155,7 @@ test1424 test1425 test1426 test1427 \
 test1428 test1429 test1430 test1431 test1432 test1433 test1434 test1435 \
 test1436 test1437 test1438 test1439 test1440 test1441 test1442 test1443 \
 test1444 test1445 test1446 test1447 test1448 test1449 test1450 test1451 \
-test1452 \
+test1452 test1453 \
 test1500 test1501 test1502 test1503 test1504 test1505 test1506 test1507 \
 test1508 test1509 test1510 test1511 test1512 test1513 test1514 test1515 \
 test1516 test1517 \
diff --git a/tests/data/test1453 b/tests/data/test1453
new file mode 100644
index 000000000..da0897184
--- /dev/null
+++ b/tests/data/test1453
@@ -0,0 +1,38 @@
+<testcase>
+<info>
+<keywords>
+Too long tftp filename
+FAILURE
+</keywords>
+</info>
+#
+# Server-side
+<reply>
+</reply>
+
+#
+# Client-side
+<client>
+<server>
+none
+</server>
+<features>
+http
+</features>
+ <name>
+Too long tftp filename
+ </name>
+ <command>
+tftp://%HOSTIP:%TFTPPORT/aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaz
+</command>
+</client>
+
+#
+# Verify data after the test has been "shot"
+<verify>
+# TFTP file name too long
+<errorcode>
+71
+</errorcode>
+</verify>
+</testcase>