kbuild: clamp SUBLEVEL to 255

BugLink: https://bugs.launchpad.net/bugs/1920246
[ Upstream commit 9b82f13e7ef316cdc0a8858f1349f4defce3f9e0 ]

Right now if SUBLEVEL becomes larger than 255 it will overflow into the
territory of PATCHLEVEL, causing havoc in userspace that tests for
specific kernel version.

While userspace code tests for MAJOR and PATCHLEVEL, it doesn't test
SUBLEVEL at any point as ABI changes don't happen in the context of
stable tree.

Thus, to avoid overflows, simply clamp SUBLEVEL to it's maximum value in
the context of LINUX_VERSION_CODE. This does not affect "make
kernelversion" and such.

Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Kelsey Skunberg <kelsey.skunberg@canonical.com>

diff --git a/Makefile b/Makefile
index a87083a184c71a3f8320c8fc09c9ce0f37bf4266..88b6b288db42c1546ca2732a07c6bb5342da3b78 100644 (file)
--- a/Makefile
+++ b/Makefile
@@ -1202,9 +1202,15 @@ define filechk_utsrelease.h
 endef
 
 define filechk_version.h
-       echo \#define LINUX_VERSION_CODE $(shell                         \
-       expr $(VERSION) \* 65536 + 0$(PATCHLEVEL) \* 256 + 0$(SUBLEVEL)); \
-       echo '#define KERNEL_VERSION(a,b,c) (((a) << 16) + ((b) << 8) + (c))'
+       if [ $(SUBLEVEL) -gt 255 ]; then                                 \
+               echo \#define LINUX_VERSION_CODE $(shell                 \
+               expr $(VERSION) \* 65536 + 0$(PATCHLEVEL) \* 256 + 255); \
+       else                                                             \
+               echo \#define LINUX_VERSION_CODE $(shell                 \
+               expr $(VERSION) \* 65536 + 0$(PATCHLEVEL) \* 256 + $(SUBLEVEL)); \
+       fi;                                                              \
+       echo '#define KERNEL_VERSION(a,b,c) (((a) << 16) + ((b) << 8) +  \
+       ((c) > 255 ? 255 : (c)))'
 endef
 
 $(version_h): FORCE