Author: lwhsu
Date: Mon Feb 10 20:53:59 2020
New Revision: 357745
URL: https://svnweb.freebsd.org/changeset/base/357745

Log:
  Restore the behavior of allowing empty string in a string sysctl
  
  Added as a special case to avoid unnecessary memory operations.
  
  Reviewed by:  delphij
  Sponsored by: The FreeBSD Foundation

Modified:
  head/sys/kern/kern_sysctl.c

Modified: head/sys/kern/kern_sysctl.c
==============================================================================
--- head/sys/kern/kern_sysctl.c Mon Feb 10 20:23:08 2020        (r357744)
+++ head/sys/kern/kern_sysctl.c Mon Feb 10 20:53:59 2020        (r357745)
@@ -1687,8 +1687,12 @@ sysctl_handle_string(SYSCTL_HANDLER_ARGS)
                return (error);
 
        if (req->newlen - req->newidx >= arg2 ||
-           req->newlen - req->newidx <= 0) {
+           req->newlen - req->newidx < 0) {
                error = EINVAL;
+       } else if (req->newlen - req->newidx == 0) {
+               sx_xlock(&sysctlstringlock);
+               ((char *)arg1)[0] = '\0';
+               sx_xunlock(&sysctlstringlock);
        } else {
                arg2 = req->newlen - req->newidx;
                tmparg = malloc(arg2, M_SYSCTLTMP, M_WAITOK);
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