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commit 33e03f9cd2be4f2cd62f93fda539cc07d9c8130e
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Author: Joan Bruguera <joanbrugueram@gmail.com>
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Date: Mon Apr 11 19:49:56 2022 +0200
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misc: Fix rare fortify crash on wchar funcs. [BZ 29030]
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If `__glibc_objsize (__o) == (size_t) -1` (i.e. `__o` is unknown size), fortify
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checks should pass, and `__whatever_alias` should be called.
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Previously, `__glibc_objsize (__o) == (size_t) -1` was explicitly checked, but
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on commit a643f60c53876b, this was moved into `__glibc_safe_or_unknown_len`.
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A comment says the -1 case should work as: "The -1 check is redundant because
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since it implies that __glibc_safe_len_cond is true.". But this fails when:
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* `__s > 1`
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* `__osz == -1` (i.e. unknown size at compile time)
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* `__l` is big enough
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* `__l * __s <= __osz` can be folded to a constant
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(I only found this to be true for `mbsrtowcs` and other functions in wchar2.h)
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In this case `__l * __s <= __osz` is false, and `__whatever_chk_warn` will be
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called by `__glibc_fortify` or `__glibc_fortify_n` and crash the program.
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This commit adds the explicit `__osz == -1` check again.
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moc crashes on startup due to this, see: https://bugs.archlinux.org/task/74041
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Minimal test case (test.c):
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#include <wchar.h>
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int main (void)
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{
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const char *hw = "HelloWorld";
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mbsrtowcs (NULL, &hw, (size_t)-1, NULL);
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return 0;
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}
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Build with:
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gcc -O2 -Wp,-D_FORTIFY_SOURCE=2 test.c -o test && ./test
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Output:
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*** buffer overflow detected ***: terminated
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Fixes: BZ #29030
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Signed-off-by: Joan Bruguera <joanbrugueram@gmail.com>
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Signed-off-by: Siddhesh Poyarekar <siddhesh@sourceware.org>
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diff --git a/debug/tst-fortify.c b/debug/tst-fortify.c
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index 1668294e48b5c63c..701bffd1d664f289 100644
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--- a/debug/tst-fortify.c
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+++ b/debug/tst-fortify.c
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@@ -1505,6 +1505,11 @@ do_test (void)
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CHK_FAIL_END
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#endif
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+ /* Bug 29030 regresion check */
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+ cp = "HelloWorld";
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+ if (mbsrtowcs (NULL, &cp, (size_t)-1, &s) != 10)
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+ FAIL ();
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+
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cp = "A";
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if (mbstowcs (wenough, cp, 10) != 1
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|| wcscmp (wenough, L"A") != 0)
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diff --git a/misc/sys/cdefs.h b/misc/sys/cdefs.h
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index a17ae0ed87e6163f..404496c7d6da4fb3 100644
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--- a/misc/sys/cdefs.h
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+++ b/misc/sys/cdefs.h
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@@ -143,13 +143,13 @@
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|| (__builtin_constant_p (__l) && (__l) > 0))
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/* Length is known to be safe at compile time if the __L * __S <= __OBJSZ
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- condition can be folded to a constant and if it is true. The -1 check is
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- redundant because since it implies that __glibc_safe_len_cond is true. */
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+ condition can be folded to a constant and if it is true, or unknown (-1) */
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#define __glibc_safe_or_unknown_len(__l, __s, __osz) \
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- (__glibc_unsigned_or_positive (__l) \
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- && __builtin_constant_p (__glibc_safe_len_cond ((__SIZE_TYPE__) (__l), \
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- __s, __osz)) \
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- && __glibc_safe_len_cond ((__SIZE_TYPE__) (__l), __s, __osz))
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+ ((__osz) == (__SIZE_TYPE__) -1 \
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+ || (__glibc_unsigned_or_positive (__l) \
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+ && __builtin_constant_p (__glibc_safe_len_cond ((__SIZE_TYPE__) (__l), \
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+ (__s), (__osz))) \
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+ && __glibc_safe_len_cond ((__SIZE_TYPE__) (__l), (__s), (__osz))))
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/* Conversely, we know at compile time that the length is unsafe if the
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__L * __S <= __OBJSZ condition can be folded to a constant and if it is
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