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authorJoan Bruguera <joanbrugueram@gmail.com>2022-04-11 19:49:56 +0200
committerSiddhesh Poyarekar <siddhesh@sourceware.org>2022-04-25 17:32:30 +0530
commit33e03f9cd2be4f2cd62f93fda539cc07d9c8130e (patch)
treebd58ea330df9eab5caac54b3ebcfe65e94c79954 /misc/sys
parent693517b92293e7ee817acf38f227f483248d33af (diff)
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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 <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>
Diffstat (limited to 'misc/sys')
-rw-r--r--misc/sys/cdefs.h12
1 files changed, 6 insertions, 6 deletions
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