kernel/sysctl.c: detect overflows when converting to int

When converting unsigned long to int overflows may occur.  These currently
are not detected when writing to the sysctl file system.

E.g. on a system where int has 32 bits and long has 64 bits
  echo 0x800001234 > /proc/sys/kernel/threads-max
has the same effect as
  echo 0x1234 > /proc/sys/kernel/threads-max

The patch adds the missing check in do_proc_dointvec_conv.

With the patch an overflow will result in an error EINVAL when writing to
the the sysctl file system.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 9 insertions, 1 deletions

diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 3c0998426b57..2082b1a88fb9 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -1981,7 +1981,15 @@ static int do_proc_dointvec_conv(bool *negp, unsigned long *lvalp,
                                  int write, void *data)
 {
         if (write) {
-                *valp = *negp ? -*lvalp : *lvalp;
+                if (*negp) {
+                        if (*lvalp > (unsigned long) INT_MAX + 1)
+                                return -EINVAL;
+                        *valp = -*lvalp;
+                } else {
+                        if (*lvalp > (unsigned long) INT_MAX)
+                                return -EINVAL;
+                        *valp = *lvalp;
+                }
         } else {
                 int val = *valp;
                 if (val < 0) {