From 33e03f9cd2be4f2cd62f93fda539cc07d9c8130e Mon Sep 17 00:00:00 2001 From: Joan Bruguera Date: Mon, 11 Apr 2022 19:49:56 +0200 Subject: misc: Fix rare fortify crash on wchar funcs. [BZ 29030] 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 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 Signed-off-by: Siddhesh Poyarekar --- misc/sys/cdefs.h | 12 ++++++------ 1 file changed, 6 insertions(+), 6 deletions(-) (limited to 'misc') diff --git a/misc/sys/cdefs.h b/misc/sys/cdefs.h index 44d3826bca..f1faf8292c 100644 --- a/misc/sys/cdefs.h +++ b/misc/sys/cdefs.h @@ -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 -- cgit 1.4.1