[PATCH] kconfig: fix memory leak from range properties

[PATCH] kconfig: fix memory leak from range properties

[Masahiro Yamada]

Currently, sym_validate_range() duplicates the range string using
xstrdup(), which is overwritten by a subsequent sym_calc_value() call.
It results in a memory leak.

Instead, only the pointer should be copied.

Below is a test case, with a summary from Valgrind.

[Test Kconfig]

  config FOO
          int "foo"
          range 10 20

[Test .config]

  CONFIG_FOO=0

[Before]

  LEAK SUMMARY:
     definitely lost: 3 bytes in 1 blocks
     indirectly lost: 0 bytes in 0 blocks
       possibly lost: 0 bytes in 0 blocks
     still reachable: 17,465 bytes in 21 blocks
          suppressed: 0 bytes in 0 blocks

[After]

  LEAK SUMMARY:
     definitely lost: 0 bytes in 0 blocks
     indirectly lost: 0 bytes in 0 blocks
       possibly lost: 0 bytes in 0 blocks
     still reachable: 17,462 bytes in 20 blocks
          suppressed: 0 bytes in 0 blocks

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
---

 scripts/kconfig/symbol.c | 14 ++++++--------
 1 file changed, 6 insertions(+), 8 deletions(-)

diff --git a/scripts/kconfig/symbol.c b/scripts/kconfig/symbol.c
index 0572330bf8a7..a76925b46ce6 100644
--- a/scripts/kconfig/symbol.c
+++ b/scripts/kconfig/symbol.c
@@ -122,9 +122,9 @@ static long long sym_get_range_val(struct symbol *sym, int base)
 static void sym_validate_range(struct symbol *sym)
 {
 	struct property *prop;
+	struct symbol *range_sym;
 	int base;
 	long long val, val2;
-	char str[64];
 
 	switch (sym->type) {
 	case S_INT:
@@ -140,17 +140,15 @@ static void sym_validate_range(struct symbol *sym)
 	if (!prop)
 		return;
 	val = strtoll(sym->curr.val, NULL, base);
-	val2 = sym_get_range_val(prop->expr->left.sym, base);
+	range_sym = prop->expr->left.sym;
+	val2 = sym_get_range_val(range_sym, base);
 	if (val >= val2) {
-		val2 = sym_get_range_val(prop->expr->right.sym, base);
+		range_sym = prop->expr->right.sym;
+		val2 = sym_get_range_val(range_sym, base);
 		if (val <= val2)
 			return;
 	}
-	if (sym->type == S_INT)
-		sprintf(str, "%lld", val2);
-	else
-		sprintf(str, "0x%llx", val2);
-	sym->curr.val = xstrdup(str);
+	sym->curr.val = range_sym->curr.val;
 }
 
 static void sym_set_changed(struct symbol *sym)
-- 
2.40.1

Re: [PATCH] kconfig: fix memory leak from range properties

[Boris Kolpackov]

Masahiro Yamada <masahiroy@kernel.org> writes:

> Currently, sym_validate_range() duplicates the range string using
> xstrdup(), which is overwritten by a subsequent sym_calc_value() call.
> It results in a memory leak.
> 
> [After]
> 
>   LEAK SUMMARY:
>      definitely lost: 0 bytes in 0 blocks
>      indirectly lost: 0 bytes in 0 blocks
>        possibly lost: 0 bytes in 0 blocks
>      still reachable: 17,462 bytes in 20 blocks
>           suppressed: 0 bytes in 0 blocks

FYI, there are quite a few other memory leaks in Kconfig (as evident from
the still reachable value in the above report). I believe I've fixed most
of them in this commit:

https://github.com/build2-packaging/kconfig/commit/cd9910e3636515b2980ce1d37d1984ccfd6b4cb9

In particular, I could load the Linux kernel configuration repeatedly
in a loop without causing any memory leaks or crashes (which were common
due to the state not being reset properly).

I believe the above commit also includes a fix for the sym_validate_range()
leak in question, though the way it's fixed is different. The potential
problem with the proposed fix is that it may be impossible to decide who
should free the shared value.