USB: w1 ds2490: Fix bug caused by improper use of altsetting array [Linux 5.1]

USB: w1 ds2490: Fix bug caused by improper use of altsetting array [Linux 5.1]

This Linux kernel change "USB: w1 ds2490: Fix bug caused by improper use of altsetting array" is included in the Linux 5.1 release. This change is authored by Alan Stern <stern [at] rowland.harvard.edu> on Mon Apr 22 11:16:04 2019 -0400. The commit for this change in Linux stable tree is c114944 (patch).

USB: w1 ds2490: Fix bug caused by improper use of altsetting array

The syzkaller USB fuzzer spotted a slab-out-of-bounds bug in the
ds2490 driver.  This bug is caused by improper use of the altsetting
array in the usb_interface structure (the array's entries are not
always stored in numerical order), combined with a naive assumption
that all interfaces probed by the driver will have the expected number
of altsettings.

The bug can be fixed by replacing references to the possibly
non-existent intf->altsetting[alt] entry with the guaranteed-to-exist
intf->cur_altsetting entry.

Signed-off-by: Alan Stern <[email protected]>
Reported-and-tested-by: [email protected]
CC: <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>

There are 6 lines of Linux source code added/deleted in this change. Code changes to Linux kernel are as follows.

 drivers/w1/masters/ds2490.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/w1/masters/ds2490.c b/drivers/w1/masters/ds2490.c
index 0f4ecfc..a9fb775 100644
--- a/drivers/w1/masters/ds2490.c
+++ b/drivers/w1/masters/ds2490.c
@@ -1016,15 +1016,15 @@ static int ds_probe(struct usb_interface *intf,
    /* alternative 3, 1ms interrupt (greatly speeds search), 64 byte bulk */
    alt = 3;
    err = usb_set_interface(dev->udev,
-       intf->altsetting[alt].desc.bInterfaceNumber, alt);
+       intf->cur_altsetting->desc.bInterfaceNumber, alt);
    if (err) {
        dev_err(&dev->udev->dev, "Failed to set alternative setting %d "
            "for %d interface: err=%d.\n", alt,
-           intf->altsetting[alt].desc.bInterfaceNumber, err);
+           intf->cur_altsetting->desc.bInterfaceNumber, err);
        goto err_out_clear;
    }

-   iface_desc = &intf->altsetting[alt];
+   iface_desc = intf->cur_altsetting;
    if (iface_desc->desc.bNumEndpoints != NUM_EP-1) {
        pr_info("Num endpoints=%d. It is not DS9490R.\n",
            iface_desc->desc.bNumEndpoints);

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