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fortify: Do not special-case 0-sized destinations

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All fake flexible arrays should have been removed now, so remove the
special casing that was avoiding checking them. If a destination claims
to be 0 sized, believe it. This is especially important for cases where
__counted_by is in use and may have a 0 element count.

Link: https://lore.kernel.org/r/20240619203105.work.747-kees@kernel.org
Signed-off-by: Kees Cook <kees@kernel.org>
This commit is contained in:
Kees Cook 2024-06-19 13:31:05 -07:00
parent d6f635bcac
commit 2003e483a8
2 changed files with 3 additions and 8 deletions
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8
include/linux/fortify-string.h
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@ -601,11 +601,7 @@ __FORTIFY_INLINE bool fortify_memcpy_chk(__kernel_size_t size,
/*
* Warn when writing beyond destination field size.
*
* We must ignore p_size_field == 0 for existing 0-element
* fake flexible arrays, until they are all converted to
* proper flexible arrays.
*
* The implementation of __builtin_*object_size() behaves
* Note the implementation of __builtin_*object_size() behaves
* like sizeof() when not directly referencing a flexible
* array member, which means there will be many bounds checks
* that will appear at run-time, without a way for them to be
@ -613,7 +609,7 @@ __FORTIFY_INLINE bool fortify_memcpy_chk(__kernel_size_t size,
* is specifically the flexible array member).
* https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101832
*/
if (p_size_field != 0 && p_size_field != SIZE_MAX &&
if (p_size_field != SIZE_MAX &&
p_size != p_size_field && p_size_field < size)
return true;

3
lib/fortify_kunit.c
View File

@ -910,10 +910,9 @@ static void fortify_test_##memfunc(struct kunit *test) \
memfunc(zero.buf, srcB, 0 + unconst); \
KUNIT_EXPECT_EQ(test, fortify_read_overflows, 0); \
KUNIT_EXPECT_EQ(test, fortify_write_overflows, 0); \
/* We currently explicitly ignore zero-sized dests. */ \
memfunc(zero.buf, srcB, 1 + unconst); \
KUNIT_EXPECT_EQ(test, fortify_read_overflows, 0); \
KUNIT_EXPECT_EQ(test, fortify_write_overflows, 0); \
KUNIT_EXPECT_EQ(test, fortify_write_overflows, 1); \
}
__fortify_test(memcpy)
__fortify_test(memmove)