BUG/MINOR: hlua: Fix memory leak in hlua_alloc

During a configuration check valgrind reports:

    ==14425== 0 bytes in 106 blocks are definitely lost in loss record 1 of 107
    ==14425==    at 0x4C2DB8F: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
    ==14425==    by 0x4C2FDEF: realloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
    ==14425==    by 0x443CFC: hlua_alloc (hlua.c:8662)
    ==14425==    by 0x5F72B11: luaM_realloc_ (in /usr/lib/x86_64-linux-gnu/liblua5.3.so.0.0.0)
    ==14425==    by 0x5F78089: luaH_free (in /usr/lib/x86_64-linux-gnu/liblua5.3.so.0.0.0)
    ==14425==    by 0x5F707D3: sweeplist (in /usr/lib/x86_64-linux-gnu/liblua5.3.so.0.0.0)
    ==14425==    by 0x5F710D0: luaC_freeallobjects (in /usr/lib/x86_64-linux-gnu/liblua5.3.so.0.0.0)
    ==14425==    by 0x5F7715D: close_state (in /usr/lib/x86_64-linux-gnu/liblua5.3.so.0.0.0)
    ==14425==    by 0x443D4C: hlua_deinit (hlua.c:9302)
    ==14425==    by 0x543F88: deinit (haproxy.c:2742)
    ==14425==    by 0x5448E7: deinit_and_exit (haproxy.c:2830)
    ==14425==    by 0x5455D9: init (haproxy.c:2044)

This is due to Lua calling `hlua_alloc()` with `ptr = NULL` and `nsize = 0`.
While `realloc` is supposed to be equivalent `free()` if the size is `0` this
is only required for a non-NULL pointer. Apparently my allocator (or valgrind)
actually allocates a zero size area if the pointer is NULL, possibly taking up
some memory for management structures.

Fix this leak by specifically handling the case where both the pointer and the
size are `0`.

This bug appears to have been introduced with the introduction of the
multi-threaded Lua, thus this fix is specific for 2.4. No backport needed.

diff --git a/src/hlua.c b/src/hlua.c
index a52a1b50ddf238e1b5cb2860e5d062f9e47e2c4d..8ad9e9f4a3460321a01cc4c25e00eb119fae2790 100644 (file)
--- a/src/hlua.c
+++ b/src/hlua.c
@@ -8640,6 +8640,9 @@ static void *hlua_alloc(void *ud, void *ptr, size_t osize, size_t nsize)
        struct hlua_mem_allocator *zone = ud;
        size_t limit, old, new;
 
+       if (unlikely(!ptr && !nsize))
+               return NULL;
+
        /* a limit of ~0 means unlimited and boot complete, so there's no need
         * for accounting anymore.
         */