sysctl: fix int -> unsigned long assignments in INT_MIN case
The following
if (val < 0)
*lvalp = (unsigned long)-val;
is incorrect because the compiler is free to assume -val to be positive
and use a sign-extend instruction for extending the bit pattern. This is
a problem if val == INT_MIN:
# echo -2147483648 >/proc/sys/dev/scsi/logging_level
# cat /proc/sys/dev/scsi/logging_level
-18446744071562067968
Cast to unsigned long before negation - that way we first sign-extend and
then negate an unsigned, which is well defined. With this:
# cat /proc/sys/dev/scsi/logging_level
-2147483648
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
Cc: Mikulas Patocka <mikulas@twibright.com>
Cc: Robert Xiao <nneonneo@gmail.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Kees Cook <keescook@chromium.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 715cc57..e69201d 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -1995,7 +1995,7 @@
int val = *valp;
if (val < 0) {
*negp = true;
- *lvalp = (unsigned long)-val;
+ *lvalp = -(unsigned long)val;
} else {
*negp = false;
*lvalp = (unsigned long)val;
@@ -2201,7 +2201,7 @@
int val = *valp;
if (val < 0) {
*negp = true;
- *lvalp = (unsigned long)-val;
+ *lvalp = -(unsigned long)val;
} else {
*negp = false;
*lvalp = (unsigned long)val;
@@ -2436,7 +2436,7 @@
unsigned long lval;
if (val < 0) {
*negp = true;
- lval = (unsigned long)-val;
+ lval = -(unsigned long)val;
} else {
*negp = false;
lval = (unsigned long)val;
@@ -2459,7 +2459,7 @@
unsigned long lval;
if (val < 0) {
*negp = true;
- lval = (unsigned long)-val;
+ lval = -(unsigned long)val;
} else {
*negp = false;
lval = (unsigned long)val;
@@ -2484,7 +2484,7 @@
unsigned long lval;
if (val < 0) {
*negp = true;
- lval = (unsigned long)-val;
+ lval = -(unsigned long)val;
} else {
*negp = false;
lval = (unsigned long)val;