6.6-stable review patch. If anyone has any objections, please let me know.
------------------
From: Kees Cook <keescook@xxxxxxxxxxxx>
[ Upstream commit 0e108725f6cc5b3be9e607f89c9fbcbb236367b7 ]
Arnd noticed we have a case where a shorter source string is being copied
into a destination byte array, but this results in a strnlen() call that
exceeds the size of the source. This is seen with -Wstringop-overread:
In file included from ../include/linux/uuid.h:11,
from ../include/linux/mod_devicetable.h:14,
from ../include/linux/cpufeature.h:12,
from ../arch/x86/coco/tdx/tdx.c:7:
../arch/x86/coco/tdx/tdx.c: In function 'tdx_panic.constprop':
../include/linux/string.h:284:9: error: 'strnlen' specified bound 64 exceeds source size 60 [-Werror=stringop-overread]
284 | memcpy_and_pad(dest, _dest_len, src, strnlen(src, _dest_len), pad); \
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
../arch/x86/coco/tdx/tdx.c:124:9: note: in expansion of macro 'strtomem_pad'
124 | strtomem_pad(message.str, msg, '\0');
| ^~~~~~~~~~~~
Use the smaller of the two buffer sizes when calling strnlen(). When
src length is unknown (SIZE_MAX), it is adjusted to use dest length,
which is what the original code did.
Reported-by: Arnd Bergmann <arnd@xxxxxxxx>
Fixes: dfbafa70bde2 ("string: Introduce strtomem() and strtomem_pad()")
Tested-by: Arnd Bergmann <arnd@xxxxxxxx>
Cc: Andy Shevchenko <andy@xxxxxxxxxx>
Cc: linux-hardening@xxxxxxxxxxxxxxx
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
include/linux/string.h | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)
diff --git a/include/linux/string.h b/include/linux/string.h
index dbfc66400050f..9e3cb6923b0ef 100644
--- a/include/linux/string.h
+++ b/include/linux/string.h
@@ -277,10 +277,12 @@ void memcpy_and_pad(void *dest, size_t dest_len, const void *src, size_t count,
*/
#define strtomem_pad(dest, src, pad) do { \
const size_t _dest_len = __builtin_object_size(dest, 1); \
+ const size_t _src_len = __builtin_object_size(src, 1); \
\
BUILD_BUG_ON(!__builtin_constant_p(_dest_len) || \
_dest_len == (size_t)-1); \
- memcpy_and_pad(dest, _dest_len, src, strnlen(src, _dest_len), pad); \
+ memcpy_and_pad(dest, _dest_len, src, \
+ strnlen(src, min(_src_len, _dest_len)), pad); \
} while (0)
/**
@@ -298,10 +300,11 @@ void memcpy_and_pad(void *dest, size_t dest_len, const void *src, size_t count,
*/
#define strtomem(dest, src) do { \
const size_t _dest_len = __builtin_object_size(dest, 1); \
+ const size_t _src_len = __builtin_object_size(src, 1); \
\
BUILD_BUG_ON(!__builtin_constant_p(_dest_len) || \
_dest_len == (size_t)-1); \
- memcpy(dest, src, min(_dest_len, strnlen(src, _dest_len))); \
+ memcpy(dest, src, strnlen(src, min(_src_len, _dest_len))); \
} while (0)
/**
--
2.42.0
