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    Subject[019/264] xhci-mem.c: Check for ring->first_seg != NULL
    3.1-stable review patch.  If anyone has any objections, please let me know.

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

    From: Kautuk Consul <consul.kautuk@gmail.com>

    commit 0e6c7f746ea99089fb3263709075c20485a479ae upstream.

    There are 2 situations wherein the xhci_ring* might not get freed:
    - When xhci_ring_alloc() -> xhci_segment_alloc() returns NULL and
    we goto the fail: label in xhci_ring_alloc. In this case, the ring
    will not get kfreed.
    - When the num_segs argument to xhci_ring_alloc is passed as 0 and
    we try to free the rung after that.
    ( This doesn't really happen as of now in the code but we seem to
    be entertaining num_segs=0 in xhci_ring_alloc )

    This should be backported to kernels as old as 2.6.31.

    Signed-off-by: Kautuk Consul <consul.kautuk@gmail.com>
    Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

    ---
    drivers/usb/host/xhci-mem.c | 22 ++++++++++++----------
    1 file changed, 12 insertions(+), 10 deletions(-)

    --- a/drivers/usb/host/xhci-mem.c
    +++ b/drivers/usb/host/xhci-mem.c
    @@ -112,18 +112,20 @@ void xhci_ring_free(struct xhci_hcd *xhc
    struct xhci_segment *seg;
    struct xhci_segment *first_seg;

    - if (!ring || !ring->first_seg)
    + if (!ring)
    return;
    - first_seg = ring->first_seg;
    - seg = first_seg->next;
    - xhci_dbg(xhci, "Freeing ring at %p\n", ring);
    - while (seg != first_seg) {
    - struct xhci_segment *next = seg->next;
    - xhci_segment_free(xhci, seg);
    - seg = next;
    + if (ring->first_seg) {
    + first_seg = ring->first_seg;
    + seg = first_seg->next;
    + xhci_dbg(xhci, "Freeing ring at %p\n", ring);
    + while (seg != first_seg) {
    + struct xhci_segment *next = seg->next;
    + xhci_segment_free(xhci, seg);
    + seg = next;
    + }
    + xhci_segment_free(xhci, first_seg);
    + ring->first_seg = NULL;
    }
    - xhci_segment_free(xhci, first_seg);
    - ring->first_seg = NULL;
    kfree(ring);
    }




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