[PATCH 3.2 060/115] usb: renesas_usbhs: avoid NULL pointer derefernce in usbhsf_pkt_handler()

[Ben Hutchings]

3.2.80-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Yoshihiro Shimoda <yoshihiro.shimoda.uh@xxxxxxxxxxx>

commit 894f2fc44f2f3f48c36c973b1123f6ab298be160 upstream.

When unexpected situation happened (e.g. tx/rx irq happened while
DMAC is used), the usbhsf_pkt_handler() was possible to cause NULL
pointer dereference like the followings:

Unable to handle kernel NULL pointer dereference at virtual address 00000000
pgd = c0004000
[00000000] *pgd=00000000
Internal error: Oops: 80000007 [#1] SMP ARM
Modules linked in: usb_f_acm u_serial g_serial libcomposite
CPU: 0 PID: 0 Comm: swapper/0 Not tainted 4.5.0-rc6-00842-gac57066-dirty #63
Hardware name: Generic R8A7790 (Flattened Device Tree)
task: c0729c00 ti: c0724000 task.ti: c0724000
PC is at 0x0
LR is at usbhsf_pkt_handler+0xac/0x118
pc : [<00000000>]    lr : [<c03257e0>]    psr: 60000193
sp : c0725db8  ip : 00000000  fp : c0725df4
r10: 00000001  r9 : 00000193  r8 : ef3ccab4
r7 : ef3cca10  r6 : eea4586c  r5 : 00000000  r4 : ef19ceb4
r3 : 00000000  r2 : 0000009c  r1 : c0725dc4  r0 : ef19ceb4

This patch adds a condition to avoid the dereference.

Fixes: e73a989 ("usb: renesas_usbhs: add DMAEngine support")
Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@xxxxxxxxxxx>
Signed-off-by: Felipe Balbi <felipe.balbi@xxxxxxxxxxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 drivers/usb/renesas_usbhs/fifo.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/drivers/usb/renesas_usbhs/fifo.c
+++ b/drivers/usb/renesas_usbhs/fifo.c
@@ -166,7 +166,8 @@ static int usbhsf_pkt_handler(struct usb
 		goto __usbhs_pkt_handler_end;
 	}
 
-	ret = func(pkt, &is_done);
+	if (likely(func))
+		ret = func(pkt, &is_done);
 
 	if (is_done)
 		__usbhsf_pkt_del(pkt);