[committed] misc: Fix rare fortify crash on wchar funcs. [BZ 29030]
Commit Message
From: Joan Bruguera <joanbrugueram@gmail.com>
Hi,
I've pushed this now, which is your fix + changes I suggested during review.
Thanks,
Siddhesh
--->8---
If `__glibc_objsize (__o) == (size_t) -1` (i.e. `__o` is unknown size), fortify
checks should pass, and `__whatever_alias` should be called.
Previously, `__glibc_objsize (__o) == (size_t) -1` was explicitly checked, but
on commit a643f60c53876b, this was moved into `__glibc_safe_or_unknown_len`.
A comment says the -1 case should work as: "The -1 check is redundant because
since it implies that __glibc_safe_len_cond is true.". But this fails when:
* `__s > 1`
* `__osz == -1` (i.e. unknown size at compile time)
* `__l` is big enough
* `__l * __s <= __osz` can be folded to a constant
(I only found this to be true for `mbsrtowcs` and other functions in wchar2.h)
In this case `__l * __s <= __osz` is false, and `__whatever_chk_warn` will be
called by `__glibc_fortify` or `__glibc_fortify_n` and crash the program.
This commit adds the explicit `__osz == -1` check again.
moc crashes on startup due to this, see: https://bugs.archlinux.org/task/74041
Minimal test case (test.c):
#include <wchar.h>
int main (void)
{
const char *hw = "HelloWorld";
mbsrtowcs (NULL, &hw, (size_t)-1, NULL);
return 0;
}
Build with:
gcc -O2 -Wp,-D_FORTIFY_SOURCE=2 test.c -o test && ./test
Output:
*** buffer overflow detected ***: terminated
Fixes: BZ #29030
Signed-off-by: Joan Bruguera <joanbrugueram@gmail.com>
Signed-off-by: Siddhesh Poyarekar <siddhesh@sourceware.org>
---
debug/tst-fortify.c | 5 +++++
misc/sys/cdefs.h | 12 ++++++------
2 files changed, 11 insertions(+), 6 deletions(-)
@@ -1504,6 +1504,11 @@ do_test (void)
CHK_FAIL_END
#endif
+ /* Bug 29030 regresion check */
+ cp = "HelloWorld";
+ if (mbsrtowcs (NULL, &cp, (size_t)-1, &s) != 10)
+ FAIL ();
+
cp = "A";
if (mbstowcs (wenough, cp, 10) != 1
|| wcscmp (wenough, L"A") != 0)
@@ -162,13 +162,13 @@
|| (__builtin_constant_p (__l) && (__l) > 0))
/* Length is known to be safe at compile time if the __L * __S <= __OBJSZ
- condition can be folded to a constant and if it is true. The -1 check is
- redundant because since it implies that __glibc_safe_len_cond is true. */
+ condition can be folded to a constant and if it is true, or unknown (-1) */
#define __glibc_safe_or_unknown_len(__l, __s, __osz) \
- (__glibc_unsigned_or_positive (__l) \
- && __builtin_constant_p (__glibc_safe_len_cond ((__SIZE_TYPE__) (__l), \
- __s, __osz)) \
- && __glibc_safe_len_cond ((__SIZE_TYPE__) (__l), __s, __osz))
+ ((__osz) == (__SIZE_TYPE__) -1 \
+ || (__glibc_unsigned_or_positive (__l) \
+ && __builtin_constant_p (__glibc_safe_len_cond ((__SIZE_TYPE__) (__l), \
+ (__s), (__osz))) \
+ && __glibc_safe_len_cond ((__SIZE_TYPE__) (__l), (__s), (__osz))))
/* Conversely, we know at compile time that the length is unsafe if the
__L * __S <= __OBJSZ condition can be folded to a constant and if it is