@@ -441,13 +441,18 @@ __FORTIFY_INLINE bool fortify_memcpy_chk(__kernel_size_t size,
#define __fortify_memcpy_chk(p, q, size, p_size, q_size, \
p_size_field, q_size_field, op) ({ \
- size_t __fortify_size = (size_t)(size); \
- WARN_ONCE(fortify_memcpy_chk(__fortify_size, p_size, q_size, \
- p_size_field, q_size_field, #op), \
+ const size_t __fortify_size = (size_t)(size); \
+ const size_t __p_size = (p_size); \
+ const size_t __q_size = (q_size); \
+ const size_t __p_size_field = (p_size_field); \
+ const size_t __q_size_field = (q_size_field); \
+ WARN_ONCE(fortify_memcpy_chk(__fortify_size, __p_size, \
+ __q_size, __p_size_field, \
+ __q_size_field, #op), \
#op ": detected field-spanning write (size %zu) of single %s (size %zu)\n", \
__fortify_size, \
"field \"" #p "\" at " __FILE__ ":" __stringify(__LINE__), \
- p_size_field); \
+ __p_size_field); \
__underlying_##op(p, q, __fortify_size); \
})
In two recent run-time memcpy() bound checking bug reports (NFS[1] and JFS[2]), the _detection_ was working correctly (in the sense that the requested copy size was larger than the destination field size), but the _warning text_ was showing the destination field size as SIZE_MAX ("unknown size"). This should be impossible, since the detection function will explicitly give up if the destination field size is unknown. For example, the JFS warning was: memcpy: detected field-spanning write (size 132) of single field "ip->i_link" at fs/jfs/namei.c:950 (size 18446744073709551615) Other cases of this warning (e.g.[3]) have reported correctly, and the reproducer only happens under GCC (at least 10.2 and 12.1), so this currently appears to be a GCC bug. Explicitly capturing the __builtin_object_size() results in const temporary variables fixes the report. For example, the JFS reproducer now correctly reports the field size (128): memcpy: detected field-spanning write (size 132) of single field "ip->i_link" at fs/jfs/namei.c:950 (size 128) Examination of the .text delta (which is otherwise identical), shows the literal value used in the report changing: - mov $0xffffffffffffffff,%rcx + mov $0x80,%ecx [1] https://lore.kernel.org/lkml/Y0zEzZwhOxTDcBTB@codemonkey.org.uk/ [2] https://syzkaller.appspot.com/bug?id=23d613df5259b977dac1696bec77f61a85890e3d [3] https://lore.kernel.org/all/202210110948.26b43120-yujie.liu@intel.com/ Cc: "Dr. David Alan Gilbert" <linux@treblig.org> Cc: llvm@lists.linux.dev Cc: linux-hardening@vger.kernel.org Signed-off-by: Kees Cook <keescook@chromium.org> --- include/linux/fortify-string.h | 13 +++++++++---- 1 file changed, 9 insertions(+), 4 deletions(-)