USB: fix usbmon BUG trigger

commit 46eb14a6e1585d99c1b9f58d0e7389082a5f466b upstream.

Automated tests triggered this by opening usbmon and accessing the
mmap while simultaneously resizing the buffers. This bug was with
us since 2006, because typically applications only size the buffers
once and thus avoid racing. Reported by Kirill A. Shutemov.

Reported-by: <syzbot+f9831b881b3e849829fc@syzkaller.appspotmail.com>
Signed-off-by: Pete Zaitcev <zaitcev@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/usb/mon/mon_bin.c b/drivers/usb/mon/mon_bin.c
index 9a62e89d6dc0b720cf7cdd59b1530be024187c28..bbec84dd34fb55b8292a0d66d3fdecf7684e25e6 100644 (file)
--- a/drivers/usb/mon/mon_bin.c
+++ b/drivers/usb/mon/mon_bin.c
@@ -1000,7 +1000,9 @@ static long mon_bin_ioctl(struct file *file, unsigned int cmd, unsigned long arg
                break;
 
        case MON_IOCQ_RING_SIZE:
+               mutex_lock(&rp->fetch_lock);
                ret = rp->b_size;
+               mutex_unlock(&rp->fetch_lock);
                break;
 
        case MON_IOCT_RING_SIZE:
@@ -1227,12 +1229,16 @@ static int mon_bin_vma_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
        unsigned long offset, chunk_idx;
        struct page *pageptr;
 
+       mutex_lock(&rp->fetch_lock);
        offset = vmf->pgoff << PAGE_SHIFT;
-       if (offset >= rp->b_size)
+       if (offset >= rp->b_size) {
+               mutex_unlock(&rp->fetch_lock);
                return VM_FAULT_SIGBUS;
+       }
        chunk_idx = offset / CHUNK_SIZE;
        pageptr = rp->b_vec[chunk_idx].pg;
        get_page(pageptr);
+       mutex_unlock(&rp->fetch_lock);
        vmf->page = pageptr;
        return 0;
 }