• J. Bruce Fields's avatar
    nfsd4: fix corruption of NFSv4 read data · 15b23ef5
    J. Bruce Fields authored
    The calculation of page_ptr here is wrong in the case the read doesn't
    start at an offset that is a multiple of a page.
    
    The result is that nfs4svc_encode_compoundres sets rq_next_page to a
    value one too small, and then the loop in svc_free_res_pages may
    incorrectly fail to clear a page pointer in rq_respages[].
    
    Pages left in rq_respages[] are available for the next rpc request to
    use, so xdr data may be written to that page, which may hold data still
    waiting to be transmitted to the client or data in the page cache.
    
    The observed result was silent data corruption seen on an NFSv4 client.
    
    We tag this as "fixing" 05638dc7 because that commit exposed this
    bug, though the incorrect calculation predates it.
    
    Particular thanks to Andrea Arcangeli and David Gilbert for analysis and
    testing.
    
    Fixes: 05638dc7 "nfsd4: simplify server xdr->next_page use"
    Cc: stable@vger.kernel.org
    Reported-by: default avatarAndrea Arcangeli <aarcange@redhat.com>
    Tested-by: default avatar"Dr. David Alan Gilbert" <dgilbert@redhat.com>
    Signed-off-by: default avatarJ. Bruce Fields <bfields@redhat.com>
    15b23ef5
nfs4xdr.c 102 KB