• Dave Chinner's avatar
    iomap: dio data corruption and spurious errors when pipes fill · 4721a601
    Dave Chinner authored
    When doing direct IO to a pipe for do_splice_direct(), then pipe is
    trivial to fill up and overflow as it can only hold 16 pages. At
    this point bio_iov_iter_get_pages() then returns -EFAULT, and we
    abort the IO submission process. Unfortunately, iomap_dio_rw()
    propagates the error back up the stack.
    
    The error is converted from the EFAULT to EAGAIN in
    generic_file_splice_read() to tell the splice layers that the pipe
    is full. do_splice_direct() completely fails to handle EAGAIN errors
    (it aborts on error) and returns EAGAIN to the caller.
    
    copy_file_write() then completely fails to handle EAGAIN as well,
    and so returns EAGAIN to userspace, having failed to copy the data
    it was asked to.
    
    Avoid this whole steaming pile of fail by having iomap_dio_rw()
    silently swallow EFAULT errors and so do short reads.
    
    To make matters worse, iomap_dio_actor() has a stale data exposure
    bug bio_iov_iter_get_pages() fails - it does not zero the tail block
    that it may have been left uncovered by partial IO. Fix the error
    handling case to drop to the sub-block zeroing rather than
    immmediately returning the -EFAULT error.
    Signed-off-by: default avatarDave Chinner <dchinner@redhat.com>
    Reviewed-by: default avatarDarrick J. Wong <darrick.wong@oracle.com>
    Reviewed-by: default avatarChristoph Hellwig <hch@lst.de>
    Signed-off-by: default avatarDarrick J. Wong <darrick.wong@oracle.com>
    4721a601
iomap.c 53.1 KB