replace incorrect strscpy use in FORTIFY_SOURCE (077d2ba5) · Commits · 戴 / test

Using strscpy was wrong because FORTIFY_SOURCE is passing the maximum possible size of the outermost object, but strscpy defines the count parameter as the exact buffer size, so this could copy past the end of the source. This would still be wrong with the planned usage of __builtin_object_size(p, 1) for intra-object overflow checks since it's the maximum possible size of the specified object with no guarantee of it being that large. Reuse of the fortified functions like this currently makes the runtime error reporting less precise but that can be improved later on. Noticed by Dave Jones and KASAN. Signed-off-by:

Daniel Micay <danielmicay@gmail.com> Acked-by:

Kees Cook <keescook@chromium.org> Reported-by:

Dave Jones <davej@codemonkey.org.uk> Signed-off-by:

Linus Torvalds <torvalds@linux-foundation.org>

include/linux/string.h

+12 −11

Original line number	Diff line number	Diff line
		@@ -202,17 +202,6 @@ void __read_overflow2(void) __compiletime_error("detected read beyond size of ob
		void __write_overflow(void) __compiletime_error("detected write beyond size of object passed as 1st parameter");

		#if !defined(__NO_FORTIFY) && defined(__OPTIMIZE__) && defined(CONFIG_FORTIFY_SOURCE)
		__FORTIFY_INLINE char strcpy(char p, const char *q)
		{
		size_t p_size = __builtin_object_size(p, 0);
		size_t q_size = __builtin_object_size(q, 0);
		if (p_size == (size_t)-1 && q_size == (size_t)-1)
		return __builtin_strcpy(p, q);
		if (strscpy(p, q, p_size < q_size ? p_size : q_size) < 0)
		fortify_panic(__func__);
		return p;
		}

		__FORTIFY_INLINE char strncpy(char p, const char *q, __kernel_size_t size)
		{
		size_t p_size = __builtin_object_size(p, 0);
		@@ -391,6 +380,18 @@ __FORTIFY_INLINE void kmemdup(const void p, size_t size, gfp_t gfp)
		fortify_panic(__func__);
		return __real_kmemdup(p, size, gfp);
		}

		/* defined after fortified strlen and memcpy to reuse them */
		__FORTIFY_INLINE char strcpy(char p, const char *q)
		{
		size_t p_size = __builtin_object_size(p, 0);
		size_t q_size = __builtin_object_size(q, 0);
		if (p_size == (size_t)-1 && q_size == (size_t)-1)
		return __builtin_strcpy(p, q);
		memcpy(p, q, strlen(q) + 1);
		return p;
		}

		#endif

		#endif /* _LINUX_STRING_H_ */

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