Provide some anti-footshooting. Don't allow the user to set the interval

for acctwatch() runs to be negative or zero as this could result in either
a possible hang (or panic if INVARIANTS is on).  Previously the accounting
code handled the <= 0 case by calling acctwatch on every clock tick (eww!)
due to an implementation detail of callout_reset().  (Tick counts of
<= 0 are converted to 1).

MFC after:	3 days

1 files changed, 23 insertions, 2 deletions

diff --git a/sys/kern/kern_acct.c b/sys/kern/kern_acct.c
index 6a66da1..ffc9496 100644
--- a/sys/kern/kern_acct.c
+++ b/sys/kern/kern_acct.c
@@ -122,8 +122,29 @@ SYSCTL_INT(_kern, OID_AUTO, acct_resume, CTLFLAG_RW,
 	&acctresume, 0, "percentage of free disk space above which accounting resumes");
 
 static int acctchkfreq = 15;	/* frequency (in seconds) to check space */
-SYSCTL_INT(_kern, OID_AUTO, acct_chkfreq, CTLFLAG_RW,
-	&acctchkfreq, 0, "frequency for checking the free space");
+
+static int
+sysctl_acct_chkfreq(SYSCTL_HANDLER_ARGS)
+{
+	int error, value;
+
+	/* Write out the old value. */
+	error = SYSCTL_OUT(req, &acctchkfreq, sizeof(int));
+	if (error || req->newptr == NULL)
+		return (error);
+
+	/* Read in and verify the new value. */
+	error = SYSCTL_IN(req, &value, sizeof(int));
+	if (error)
+		return (error);
+	if (value <= 0)
+		return (EINVAL);
+	acctchkfreq = value;
+	return (0);
+}
+SYSCTL_PROC(_kern, OID_AUTO, acct_chkfreq, CTLTYPE_INT|CTLFLAG_RW,
+    &acctchkfreq, 0, sysctl_acct_chkfreq, "I",
+    "frequency for checking the free space");
 
 SYSCTL_INT(_kern, OID_AUTO, acct_suspended, CTLFLAG_RD, &acct_suspended, 0,
 	"Accounting suspended or not");