[PATCH] ISDN: fix drivers, by handling errors thrown by ->readstat()

This is a particularly ugly on-failure bug, possibly security, since the
lack of error handling here is covering up another class of bug: failure to
handle copy_to_user() return values.

The I4L API function ->readstat() returns an integer, and by looking at
several existing driver implementations, it is clear that a negative return
value was meant to indicate an error.

Given that several drivers already return a negative value indicating an
errno-style error, the current code would blindly accept that [negative]
value as a valid amount of bytes read.  Obvious damage ensues.

Correcting ->readstat() handling to properly notice errors fixes the
existing code to work correctly on error, and enables future patches to
more easily indicate errors during operation.

Signed-off-by: Jeff Garzik <jeff@garzik.org>
Cc: Karsten Keil <kkeil@suse.de>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 6 insertions, 3 deletions

diff --git a/drivers/isdn/i4l/isdn_common.c b/drivers/isdn/i4l/isdn_common.c
index c3d79eef9e32..69aee2602aa6 100644
--- a/drivers/isdn/i4l/isdn_common.c
+++ b/drivers/isdn/i4l/isdn_common.c
@@ -1134,9 +1134,12 @@ isdn_read(struct file *file, char __user *buf, size_t count, loff_t * off)
                 if (dev->drv[drvidx]->interface->readstat) {
                         if (count > dev->drv[drvidx]->stavail)
                                 count = dev->drv[drvidx]->stavail;
-                        len = dev->drv[drvidx]->interface->
-                                readstat(buf, count, drvidx,
-                                         isdn_minor2chan(minor));
+                        len = dev->drv[drvidx]->interface->readstat(buf, count,
+                                                drvidx, isdn_minor2chan(minor));
+                        if (len < 0) {
+                                retval = len;
+                                goto out;
+                        }
                 } else {
                         len = 0;
                 }