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    Subject[PATCH 3.16 141/370] USB: gadgetfs: fix unbounded memory allocation bug
    3.16.42-rc1 review patch.  If anyone has any objections, please let me know.

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

    From: Alan Stern <stern@rowland.harvard.edu>

    commit faab50984fe6636e616c7cc3d30308ba391d36fd upstream.

    Andrey Konovalov reports that fuzz testing with syzkaller causes a
    KASAN warning in gadgetfs:

    BUG: KASAN: slab-out-of-bounds in dev_config+0x86f/0x1190 at addr ffff88003c47e160
    Write of size 65537 by task syz-executor0/6356
    CPU: 3 PID: 6356 Comm: syz-executor0 Not tainted 4.9.0-rc7+ #19
    Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
    ffff88003c107ad8 ffffffff81f96aba ffffffff3dc11ef0 1ffff10007820eee
    ffffed0007820ee6 ffff88003dc11f00 0000000041b58ab3 ffffffff8598b4c8
    ffffffff81f96828 ffffffff813fb4a0 ffff88003b6eadc0 ffff88003c107738
    Call Trace:
    [< inline >] __dump_stack lib/dump_stack.c:15
    [<ffffffff81f96aba>] dump_stack+0x292/0x398 lib/dump_stack.c:51
    [<ffffffff817e4dec>] kasan_object_err+0x1c/0x70 mm/kasan/report.c:159
    [< inline >] print_address_description mm/kasan/report.c:197
    [<ffffffff817e5080>] kasan_report_error+0x1f0/0x4e0 mm/kasan/report.c:286
    [<ffffffff817e5705>] kasan_report+0x35/0x40 mm/kasan/report.c:306
    [< inline >] check_memory_region_inline mm/kasan/kasan.c:308
    [<ffffffff817e3fb9>] check_memory_region+0x139/0x190 mm/kasan/kasan.c:315
    [<ffffffff817e4044>] kasan_check_write+0x14/0x20 mm/kasan/kasan.c:326
    [< inline >] copy_from_user arch/x86/include/asm/uaccess.h:689
    [< inline >] ep0_write drivers/usb/gadget/legacy/inode.c:1135
    [<ffffffff83228caf>] dev_config+0x86f/0x1190 drivers/usb/gadget/legacy/inode.c:1759
    [<ffffffff817fdd55>] __vfs_write+0x5d5/0x760 fs/read_write.c:510
    [<ffffffff817ff650>] vfs_write+0x170/0x4e0 fs/read_write.c:560
    [< inline >] SYSC_write fs/read_write.c:607
    [<ffffffff81803a5b>] SyS_write+0xfb/0x230 fs/read_write.c:599
    [<ffffffff84f47ec1>] entry_SYSCALL_64_fastpath+0x1f/0xc2

    Indeed, there is a comment saying that the value of len is restricted
    to a 16-bit integer, but the code doesn't actually do this.

    This patch fixes the warning. It replaces the comment with a
    computation that forces the amount of data copied from the user in
    ep0_write() to be no larger than the wLength size for the control
    transfer, which is a 16-bit quantity.

    Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
    Reported-by: Andrey Konovalov <andreyknvl@google.com>
    Tested-by: Andrey Konovalov <andreyknvl@google.com>
    Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>
    [bwh: Backported to 3.16: adjust filename]
    Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
    ---
    drivers/usb/gadget/inode.c | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    --- a/drivers/usb/gadget/inode.c
    +++ b/drivers/usb/gadget/inode.c
    @@ -1200,7 +1200,7 @@ ep0_write (struct file *fd, const char _
    /* data and/or status stage for control request */
    } else if (dev->state == STATE_DEV_SETUP) {

    - /* IN DATA+STATUS caller makes len <= wLength */
    + len = min_t(size_t, len, dev->setup_wLength);
    if (dev->setup_in) {
    retval = setup_req (dev->gadget->ep0, dev->req, len);
    if (retval == 0) {
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