Hi, Sergey,

thanks for the patch!

See my comments below.

Sergey

From: Mike Pall <mike>

Reported by pwnhacker0x18.

(cherry picked from commit 4fc48c50fe3f3f5a9680bada5c0c0d0d7eb345a3)

When compiling `string.format()` with a huge sequence of elements, it is
possible that too many KGC IRs underflow the IR buffer. This patch
limits the maximum number of `string.format()` elements to be compiled
to 100.

Sergey Kaplun:
* added the description and the test for the problem

Part of tarantool/tarantool#10199
---

Branch: https://github.com/tarantool/luajit/tree/skaplun/lj-1203-limit-format-elements
Related issues:
* https://github.com/tarantool/tarantool/issues/10199
* https://github.com/LuaJIT/LuaJIT/issues/1203

 src/lj_ffrecord.c                             |  2 ++
 .../lj-1203-limit-format-elements.test.lua    | 28 +++++++++++++++++++
 2 files changed, 30 insertions(+)
 create mode 100644 test/tarantool-tests/lj-1203-limit-format-elements.test.lua

diff --git a/src/lj_ffrecord.c b/src/lj_ffrecord.c
index d5fc081e..3b82d044 100644
--- a/src/lj_ffrecord.c
+++ b/src/lj_ffrecord.c
@@ -962,6 +962,7 @@ static void LJ_FASTCALL recff_string_format(jit_State *J, RecordFFData *rd)
   TRef hdr, tr;
   FormatState fs;
   SFormat sf;
+  int nfmt = 0;
   /* Specialize to the format string. */
   emitir(IRTG(IR_EQ, IRT_STR), trfmt, lj_ir_kstr(J, fmt));
   tr = hdr = recff_bufhdr(J);
@@ -1031,6 +1032,7 @@ static void LJ_FASTCALL recff_string_format(jit_State *J, RecordFFData *rd)
       recff_nyiu(J, rd);
       return;
     }
+    if (++nfmt > 100) lj_trace_err(J, LJ_TRERR_TRACEOV);
   }
   J->base[0] = emitir(IRT(IR_BUFSTR, IRT_STR), tr, hdr);
 }
diff --git a/test/tarantool-tests/lj-1203-limit-format-elements.test.lua b/test/tarantool-tests/lj-1203-limit-format-elements.test.lua
new file mode 100644
index 00000000..f17d4e37
--- /dev/null
+++ b/test/tarantool-tests/lj-1203-limit-format-elements.test.lua
@@ -0,0 +1,28 @@
+local tap = require('tap')
+
+-- Test file to demonstrate LuaJIT incorrect recording of
+-- `string.format()` function with huge amount of elements.
+-- See also: https://github.com/LuaJIT/LuaJIT/issues/1173.

+
+local test = tap.test('lj-1203-limit-format-elements'):skipcond({
+  ['Test requires JIT enabled'] = not jit.status(),
+})
+
+test:plan(2)
+
+jit.opt.start('hotloop=1')
+
+-- XXX: Use a huge amount of format elements to process, which
+-- creates a lot of string constants.
+local NELEMENTS = 25000

Why 25000? It is reproduced with 10000 as well.

+local fmt = ('%'):rep(NELEMENTS * 2)
+local expected = ('%'):rep(NELEMENTS)
+local result
+for _ = 1, 4 do
+  result = fmt:format()
+end
+
+test:ok(true, 'no IR buffer underflow')

+test:is(result, expected, 'correct result')
+
+test:done(true)