2017-07-06 10:06:39

by Colin King

Subject: [PATCH] usb: storage: return on error to avoid a null pointer dereference

From: Colin Ian King <[email protected]>

When us->extra is null the driver is not initialized, however, a
later call to osd200_scsi_to_ata is made that dereferences
us->extra, causing a null pointer dereference. The code
currently detects and reports that the driver is not initialized;
add a return to avoid the subsequent dereference issue in this
check.

Detected by CoverityScan, CID#100308 ("Dereference after null check")

Signed-off-by: Colin Ian King <[email protected]>
---
drivers/usb/storage/isd200.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/usb/storage/isd200.c b/drivers/usb/storage/isd200.c
index fba4005dd737..174ad60679e7 100644
--- a/drivers/usb/storage/isd200.c
+++ b/drivers/usb/storage/isd200.c
@@ -1529,8 +1529,10 @@ static void isd200_ata_command(struct scsi_cmnd *srb, struct us_data *us)

/* Make sure driver was initialized */

- if (us->extra == NULL)
+ if (us->extra == NULL) {
usb_stor_dbg(us, "ERROR Driver not initialized\n");
+ return;
+ }

scsi_set_resid(srb, 0);
/* scsi_bufflen might change in protocol translation to ata */
--
2.11.0

2017-07-06 14:45:13

by Alan Stern

Subject: Re: [PATCH] usb: storage: return on error to avoid a null pointer dereference

On Thu, 6 Jul 2017, Colin King wrote:

> From: Colin Ian King <[email protected]>
>
> When us->extra is null the driver is not initialized, however, a
> later call to osd200_scsi_to_ata is made that dereferences
> us->extra, causing a null pointer dereference. The code
> currently detects and reports that the driver is not initialized;
> add a return to avoid the subsequent dereference issue in this
> check.
>
> Detected by CoverityScan, CID#100308 ("Dereference after null check")
>
> Signed-off-by: Colin Ian King <[email protected]>
> ---
> drivers/usb/storage/isd200.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/usb/storage/isd200.c b/drivers/usb/storage/isd200.c
> index fba4005dd737..174ad60679e7 100644
> --- a/drivers/usb/storage/isd200.c
> +++ b/drivers/usb/storage/isd200.c
> @@ -1529,8 +1529,10 @@ static void isd200_ata_command(struct scsi_cmnd *srb, struct us_data *us)
>
> /* Make sure driver was initialized */
>
> - if (us->extra == NULL)
> + if (us->extra == NULL) {
> usb_stor_dbg(us, "ERROR Driver not initialized\n");
> + return;
> + }

Good catch, but before returning you need to set

srb->result = DID_ERROR << 16;

so that the SCSI layer will realize the command wasn't handled.

Alan Stern

>
> scsi_set_resid(srb, 0);
> /* scsi_bufflen might change in protocol translation to ata */
>