[PATCH] sysctl: fix int -> unsigned long assignments in INT_MIN case

[Ilya Dryomov]

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 <idryo...@gmail.com>
---
 kernel/sysctl.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 19b62b522158..0b4092b9fa00 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -1995,7 +1995,7 @@ static int do_proc_dointvec_conv(bool *negp, unsigned 
long *lvalp,
                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 @@ static int do_proc_dointvec_minmax_conv(bool *negp, 
unsigned long *lvalp,
                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 @@ static int do_proc_dointvec_jiffies_conv(bool *negp, 
unsigned long *lvalp,
                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 @@ static int do_proc_dointvec_userhz_jiffies_conv(bool 
*negp, unsigned long *lvalp
                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 @@ static int do_proc_dointvec_ms_jiffies_conv(bool *negp, 
unsigned long *lvalp,
                unsigned long lval;
                if (val < 0) {
                        *negp = true;
-                       lval = (unsigned long)-val;
+                       lval = -(unsigned long)val;
                } else {
                        *negp = false;
                        lval = (unsigned long)val;
-- 
1.9.3

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