Author: mjg
Date: Tue Mar 25 23:30:35 2014
New Revision: 263755
URL: http://svnweb.freebsd.org/changeset/base/263755
Log:
Document a known problem with handling the process intended to receive
SIGIO in /dev/devctl.
Suggested by: adrian
MFC after: 6 days
Modified:
head/sys/kern/subr_bus.c
Modified: head/sys/kern/subr_bus.c
==============================================================================
--- head/sys/kern/subr_bus.c Tue Mar 25 23:19:45 2014 (r263754)
+++ head/sys/kern/subr_bus.c Tue Mar 25 23:30:35 2014 (r263755)
@@ -490,6 +490,21 @@ devioctl(struct cdev *dev, u_long cmd, c
devsoftc.nonblock = 0;
return (0);
case FIOASYNC:
+ /*
+ * FIXME:
+ * Since this is a simple assignment there is no guarantee that
+ * devsoftc.async_proc consumers will get a valid pointer.
+ *
+ * Example scenario where things break (processes A and B):
+ * 1. A opens devctl
+ * 2. A sends fd to B
+ * 3. B sets itself as async_proc
+ * 4. B exits
+ *
+ * However, normally this requires root privileges and the only
+ * in-tree consumer does not behave in a dangerous way so the
+ * issue is not critical.
+ */
if (*(int*)data)
devsoftc.async_proc = td->td_proc;
else
@@ -575,6 +590,7 @@ devctl_queue_data_f(char *data, int flag
cv_broadcast(&devsoftc.cv);
mtx_unlock(&devsoftc.mtx);
selwakeup(&devsoftc.sel);
+ /* XXX see a comment in devioctl */
p = devsoftc.async_proc;
if (p != NULL) {
PROC_LOCK(p);
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