3.16.83-rc1 review patch. If anyone has any objections, please let me know.
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From: Pete Zaitcev zaitcev@redhat.com
commit 19e6317d24c25ee737c65d1ffb7483bdda4bb54a upstream.
The problem arises because our read() function grabs a lock of the circular buffer, finds something of interest, then invokes copy_to_user() straight from the buffer, which in turn takes mm->mmap_sem. In the same time, the callback mon_bin_vma_fault() is invoked under mm->mmap_sem. It attempts to take the fetch lock and deadlocks.
This patch does away with protecting of our page list with any semaphores, and instead relies on the kernel not close the device while mmap is active in a process.
In addition, we prohibit re-sizing of a buffer while mmap is active. This way, when (now unlocked) fault is processed, it works with the page that is intended to be mapped-in, and not some other random page. Note that this may have an ABI impact, but hopefully no legitimate program is this wrong.
Signed-off-by: Pete Zaitcev zaitcev@redhat.com Reported-by: syzbot+56f9673bb4cdcbeb0e92@syzkaller.appspotmail.com Reviewed-by: Alan Stern stern@rowland.harvard.edu Fixes: 46eb14a6e158 ("USB: fix usbmon BUG trigger") Link: https://lore.kernel.org/r/20191204203941.3503452b@suzdal.zaitcev.lan Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org Signed-off-by: Ben Hutchings ben@decadent.org.uk --- drivers/usb/mon/mon_bin.c | 32 +++++++++++++++++++++----------- 1 file changed, 21 insertions(+), 11 deletions(-)
--- a/drivers/usb/mon/mon_bin.c +++ b/drivers/usb/mon/mon_bin.c @@ -1034,12 +1034,18 @@ static long mon_bin_ioctl(struct file *f
mutex_lock(&rp->fetch_lock); spin_lock_irqsave(&rp->b_lock, flags); - mon_free_buff(rp->b_vec, rp->b_size/CHUNK_SIZE); - kfree(rp->b_vec); - rp->b_vec = vec; - rp->b_size = size; - rp->b_read = rp->b_in = rp->b_out = rp->b_cnt = 0; - rp->cnt_lost = 0; + if (rp->mmap_active) { + mon_free_buff(vec, size/CHUNK_SIZE); + kfree(vec); + ret = -EBUSY; + } else { + mon_free_buff(rp->b_vec, rp->b_size/CHUNK_SIZE); + kfree(rp->b_vec); + rp->b_vec = vec; + rp->b_size = size; + rp->b_read = rp->b_in = rp->b_out = rp->b_cnt = 0; + rp->cnt_lost = 0; + } spin_unlock_irqrestore(&rp->b_lock, flags); mutex_unlock(&rp->fetch_lock); } @@ -1211,13 +1217,21 @@ mon_bin_poll(struct file *file, struct p static void mon_bin_vma_open(struct vm_area_struct *vma) { struct mon_reader_bin *rp = vma->vm_private_data; + unsigned long flags; + + spin_lock_irqsave(&rp->b_lock, flags); rp->mmap_active++; + spin_unlock_irqrestore(&rp->b_lock, flags); }
static void mon_bin_vma_close(struct vm_area_struct *vma) { + unsigned long flags; + struct mon_reader_bin *rp = vma->vm_private_data; + spin_lock_irqsave(&rp->b_lock, flags); rp->mmap_active--; + spin_unlock_irqrestore(&rp->b_lock, flags); }
/* @@ -1229,16 +1243,12 @@ static int mon_bin_vma_fault(struct vm_a unsigned long offset, chunk_idx; struct page *pageptr;
- mutex_lock(&rp->fetch_lock); offset = vmf->pgoff << PAGE_SHIFT; - if (offset >= rp->b_size) { - mutex_unlock(&rp->fetch_lock); + if (offset >= rp->b_size) 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; }