[PATCH nft v2 2/4] gmputil: add nft_gmp_free() to free strings from mpz_get_str()

[Thomas Haller <thaller@xxxxxxxxxx>]

mpz_get_str() (with NULL as first argument) will allocate a buffer using
the allocator functions (mp_set_memory_functions()). We should free
those buffers with the corresponding free function.

Add nft_gmp_free() for that and use it.

The name nft_gmp_free() is chosen because "mini-gmp.c" already has an
internal define called gmp_free(). There wouldn't be a direct conflict,
but using the same name is confusing. And maybe our own defines should
have a clear nft prefix.

Signed-off-by: Thomas Haller <thaller@xxxxxxxxxx>
---
 include/gmputil.h |  2 ++
 src/evaluate.c    |  6 +++---
 src/gmputil.c     | 21 ++++++++++++++++++++-
 3 files changed, 25 insertions(+), 4 deletions(-)

diff --git a/include/gmputil.h b/include/gmputil.h
index c524aced16ac..d1f4dcd2f1c3 100644
--- a/include/gmputil.h
+++ b/include/gmputil.h
@@ -77,4 +77,6 @@ extern void __mpz_switch_byteorder(mpz_t rop, unsigned int len);
 	__mpz_switch_byteorder(rop, len);			\
 }
 
+void nft_gmp_free(void *ptr);
+
 #endif /* NFTABLES_GMPUTIL_H */
diff --git a/src/evaluate.c b/src/evaluate.c
index 2196e92813d0..9d5f0e4d94ad 100644
--- a/src/evaluate.c
+++ b/src/evaluate.c
@@ -400,7 +400,7 @@ static int expr_evaluate_integer(struct eval_ctx *ctx, struct expr **exprp)
 		expr_error(ctx->msgs, expr,
 			   "Value %s exceeds valid range 0-%u",
 			   valstr, ctx->ectx.maxval);
-		free(valstr);
+		nft_gmp_free(valstr);
 		return -1;
 	}
 
@@ -416,8 +416,8 @@ static int expr_evaluate_integer(struct eval_ctx *ctx, struct expr **exprp)
 		expr_error(ctx->msgs, expr,
 			   "Value %s exceeds valid range 0-%s",
 			   valstr, rangestr);
-		free(valstr);
-		free(rangestr);
+		nft_gmp_free(valstr);
+		nft_gmp_free(rangestr);
 		mpz_clear(mask);
 		return -1;
 	}
diff --git a/src/gmputil.c b/src/gmputil.c
index cb26b55810c2..b4529259b031 100644
--- a/src/gmputil.c
+++ b/src/gmputil.c
@@ -184,7 +184,7 @@ int mpz_vfprintf(FILE *fp, const char *f, va_list args)
 
 			str = mpz_get_str(NULL, base, *value);
 			ok = str && fwrite(str, 1, len, fp) == len;
-			free(str);
+			nft_gmp_free(str);
 
 			if (!ok)
 				return -1;
@@ -196,3 +196,22 @@ int mpz_vfprintf(FILE *fp, const char *f, va_list args)
 	return n;
 }
 #endif
+
+void nft_gmp_free(void *ptr)
+{
+	void (*free_fcn)(void *, size_t);
+
+	/* When we get allocated memory from gmp, it was allocated via the
+	 * allocator() from mp_set_memory_functions(). We should pair the free
+	 * with the corresponding free function, which we get via
+	 * mp_get_memory_functions().
+	 *
+	 * It's not clear what the correct blk_size is. The default allocator
+	 * function of gmp just wraps free() and ignores the extra argument.
+	 * Assume 0 is fine.
+	 */
+
+	mp_get_memory_functions(NULL, NULL, &free_fcn);
+
+	(*free_fcn)(ptr, 0);
+}
-- 
2.41.0