[PATCH 5.6 146/194] usb: xhci: Fix NULL pointer dereference when enqueuing trbs from urb sg list

Greg Kroah-Hartman
2020-05-18T18:10:16Z

From: Sriharsha Allenki <sallenki@codeaurora.org>

commit 3c6f8cb92c9178fc0c66b580ea3df1fa3ac1155a upstream.

On platforms with IOMMU enabled, multiple SGs can be coalesced into one
by the IOMMU driver. In that case the SG list processing as part of the
completion of a urb on a bulk endpoint can result into a NULL pointer
dereference with the below stack dump.

<6> Unable to handle kernel NULL pointer dereference at virtual address 0000000c
<6> pgd = c0004000
<6> [0000000c] *pgd=00000000
<6> Internal error: Oops: 5 [#1] PREEMPT SMP ARM
<2> PC is at xhci_queue_bulk_tx+0x454/0x80c
<2> LR is at xhci_queue_bulk_tx+0x44c/0x80c
<2> pc : [<c08907c4>] lr : [<c08907bc>] psr: 000000d3
<2> sp : ca337c80 ip : 00000000 fp : ffffffff
<2> r10: 00000000 r9 : 50037000 r8 : 00004000
<2> r7 : 00000000 r6 : 00004000 r5 : 00000000 r4 : 00000000
<2> r3 : 00000000 r2 : 00000082 r1 : c2c1a200 r0 : 00000000
<2> Flags: nzcv IRQs off FIQs off Mode SVC_32 ISA ARM Segment none
<2> Control: 10c0383d Table: b412c06a DAC: 00000051
<6> Process usb-storage (pid: 5961, stack limit = 0xca336210)
<snip>
<2> [<c08907c4>] (xhci_queue_bulk_tx)
<2> [<c0881b3c>] (xhci_urb_enqueue)
<2> [<c0831068>] (usb_hcd_submit_urb)
<2> [<c08350b4>] (usb_sg_wait)
<2> [<c089f384>] (usb_stor_bulk_transfer_sglist)
<2> [<c089f2c0>] (usb_stor_bulk_srb)
<2> [<c089fe38>] (usb_stor_Bulk_transport)
<2> [<c089f468>] (usb_stor_invoke_transport)
<2> [<c08a11b4>] (usb_stor_control_thread)
<2> [<c014a534>] (kthread)

The above NULL pointer dereference is the result of block_len and the
sent_len set to zero after the first SG of the list when IOMMU driver
is enabled. Because of this the loop of processing the SGs has run
more than num_sgs which resulted in a sg_next on the last SG of the
list which has SG_END set.

Fix this by check for the sg before any attributes of the sg are
accessed.

[modified reason for null pointer dereference in commit message subject -Mathias]
Fixes: f9c589e142d04 ("xhci: TD-fragment, align the unsplittable case with a bounce buffer")
Cc: stable@vger.kernel.org
Signed-off-by: Sriharsha Allenki <sallenki@codeaurora.org>
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Link: https://lore.kernel.org/r/20200514110432.25564-2-mathias.nyman@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/usb/host/xhci-ring.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

--- a/drivers/usb/host/xhci-ring.c
+++ b/drivers/usb/host/xhci-ring.c
@@ -3425,8 +3425,8 @@ int xhci_queue_bulk_tx(struct xhci_hcd *
/* New sg entry */
--num_sgs;
sent_len -= block_len;
- if (num_sgs != 0) {
- sg = sg_next(sg);
+ sg = sg_next(sg);
+ if (num_sgs != 0 && sg) {
block_len = sg_dma_len(sg);
addr = (u64) sg_dma_address(sg);
addr += sent_len;