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 715cc57cc66acbec4b9c67cbbe4768fe4a1f9b7b..e69201d8094eb8bed747329afc17528c4315a6b7 100644 (file)
--- 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;