diff options
| author | Kees Cook <[email protected]> | 2022-10-28 15:32:07 -0700 |
|---|---|---|
| committer | Kees Cook <[email protected]> | 2022-10-28 16:07:01 -0700 |
| commit | 6f7630b1b5bc672b54c1285ee6aba752b446672c (patch) | |
| tree | b2788ba0eb2c4c5d5aaa2fa6dbe91c8349782672 | |
| parent | 72c3ebea375c39413d02113758319b74ecd790bd (diff) | |
fortify: Capture __bos() results in const temp vars
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/[email protected]/
[2] https://syzkaller.appspot.com/bug?id=23d613df5259b977dac1696bec77f61a85890e3d
[3] https://lore.kernel.org/all/[email protected]/
Cc: "Dr. David Alan Gilbert" <[email protected]>
Cc: [email protected]
Cc: [email protected]
Signed-off-by: Kees Cook <[email protected]>
| -rw-r--r-- | include/linux/fortify-string.h | 13 |
1 files changed, 9 insertions, 4 deletions
diff --git a/include/linux/fortify-string.h b/include/linux/fortify-string.h index 4029fe368a4f..0f00a551939a 100644 --- a/include/linux/fortify-string.h +++ b/include/linux/fortify-string.h @@ -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); \ }) |