sysctl: return -EINVAL if val violates minmax

Currently when userspace gives us a values that overflow e.g.  file-max
and other callers of __do_proc_doulongvec_minmax() we simply ignore the
new value and leave the current value untouched.

This can be problematic as it gives the illusion that the limit has
indeed be bumped when in fact it failed.  This commit makes sure to
return EINVAL when an overflow is detected.  Please note that this is a
userspace facing change.

Link: http://lkml.kernel.org/r/20190210203943.8227-4-christian@brauner.io
Signed-off-by: Christian Brauner <christian@brauner.io>
Acked-by: Luis Chamberlain <mcgrof@kernel.org>
Cc: Kees Cook <keescook@chromium.org>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Dominik Brodowski <linux@dominikbrodowski.net>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Joe Lawrence <joe.lawrence@redhat.com>
Cc: Waiman Long <longman@redhat.com>
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 d82f9161adb8f408eadaa0cdc42ae01e333ce895..f7bd1aead3bf143f12ef156467846d985117b9e9 100644 (file)
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -2886,8 +2886,10 @@ static int __do_proc_doulongvec_minmax(void *data, struct ctl_table *table, int
                        if (neg)
                                continue;
                        val = convmul * val / convdiv;
-                       if ((min && val < *min) || (max && val > *max))
-                               continue;
+                       if ((min && val < *min) || (max && val > *max)) {
+                               err = -EINVAL;
+                               break;
+                       }
                        *i = val;
                } else {
                        val = convdiv * (*i) / convmul;