[Tarantool-patches] [PATCH v1 1/1] sql: fix a segfault in hex() on receiving zeroblob

[Mergen Imeev via Tarantool-patches <tarantool-patches@dev.tarantool.org>]

This patch fixes a segmentation fault when zeroblob is received by the
SQL built-in HEX() function.

Closes #6113
---
https://github.com/tarantool/tarantool/issues/6113
https://github.com/tarantool/tarantool/tree/imeevma/gh-6113-fix-hex-segfault-2.8

 .../unreleased/gh-6113-fix-segfault-in-hex-func.md  |  4 ++++
 src/box/sql/func.c                                  | 10 ++++++++--
 test/sql-tap/engine.cfg                             |  1 +
 .../gh-6113-assert-in-hex-on-zeroblob.test.lua      | 13 +++++++++++++
 4 files changed, 26 insertions(+), 2 deletions(-)
 create mode 100644 changelogs/unreleased/gh-6113-fix-segfault-in-hex-func.md
 create mode 100755 test/sql-tap/gh-6113-assert-in-hex-on-zeroblob.test.lua

diff --git a/changelogs/unreleased/gh-6113-fix-segfault-in-hex-func.md b/changelogs/unreleased/gh-6113-fix-segfault-in-hex-func.md
new file mode 100644
index 000000000..d9bd9e279
--- /dev/null
+++ b/changelogs/unreleased/gh-6113-fix-segfault-in-hex-func.md
@@ -0,0 +1,4 @@
+## bugfix/sql
+
+* The HEX() SQL built-in function no longer throw an assert when its argument
+  consist of zero-bytes (gh-6113).
diff --git a/src/box/sql/func.c b/src/box/sql/func.c
index a5f1259cd..98670c6d7 100644
--- a/src/box/sql/func.c
+++ b/src/box/sql/func.c
@@ -1221,15 +1221,21 @@ hexFunc(sql_context * context, int argc, sql_value ** argv)
 	UNUSED_PARAMETER(argc);
 	pBlob = mem_as_bin(argv[0]);
 	n = mem_len_unsafe(argv[0]);
+	assert((argv[0]->flags & MEM_Zero) == 0 ||
+	       argv[0]->type == MEM_TYPE_BIN);
+	int zero_len = (argv[0]->flags & MEM_Zero) == 0 ? 0 : argv[0]->u.nZero;
 	assert(pBlob == mem_as_bin(argv[0]));	/* No encoding change */
 	z = zHex = contextMalloc(context, ((i64) n) * 2 + 1);
 	if (zHex) {
-		for (i = 0; i < n; i++, pBlob++) {
+		for (i = 0; i < n - zero_len; i++, pBlob++) {
 			unsigned char c = *pBlob;
 			*(z++) = hexdigits[(c >> 4) & 0xf];
 			*(z++) = hexdigits[c & 0xf];
 		}
-		*z = 0;
+		assert(i == n || (argv[0]->flags & MEM_Zero) != 0);
+		assert(n == zero_len + i);
+		memset(z, '0', 2 * zero_len);
+		z[2 * zero_len] = '\0';
 		sql_result_text(context, zHex, n * 2, sql_free);
 	}
 }
diff --git a/test/sql-tap/engine.cfg b/test/sql-tap/engine.cfg
index 8e15625f4..9f1811481 100644
--- a/test/sql-tap/engine.cfg
+++ b/test/sql-tap/engine.cfg
@@ -22,6 +22,7 @@
     },
     "gh-6157-unnecessary-free-on-string.test.lua": {},
     "gh-4077-iproto-execute-no-bind.test.lua": {},
+    "gh-6113-assert-in-hex-on-zeroblob.test.lua": {},
     "*": {
         "memtx": {"engine": "memtx"},
         "vinyl": {"engine": "vinyl"}
diff --git a/test/sql-tap/gh-6113-assert-in-hex-on-zeroblob.test.lua b/test/sql-tap/gh-6113-assert-in-hex-on-zeroblob.test.lua
new file mode 100755
index 000000000..91a29a5b4
--- /dev/null
+++ b/test/sql-tap/gh-6113-assert-in-hex-on-zeroblob.test.lua
@@ -0,0 +1,13 @@
+#!/usr/bin/env tarantool
+local test = require("sqltester")
+test:plan(1)
+
+test:do_execsql_test(
+    "gh-6113",
+    [[
+        SELECT hex(zeroblob(0)), hex(zeroblob(10));
+    ]], {
+        '', '00000000000000000000'
+    })
+
+test:finish_test()
-- 
2.25.1