• David Howells's avatar
    FS-Cache: Handle a write to the page immediately beyond the EOF marker · 495b046a
    David Howells authored
    commit 102f4d90 upstream.
    
    Handle a write being requested to the page immediately beyond the EOF
    marker on a cache object.  Currently this gets an assertion failure in
    CacheFiles because the EOF marker is used there to encode information about
    a partial page at the EOF - which could lead to an unknown blank spot in
    the file if we extend the file over it.
    
    The problem is actually in fscache where we check the index of the page
    being written against store_limit.  store_limit is set to the number of
    pages that we're allowed to store by fscache_set_store_limit() - which
    means it's one more than the index of the last page we're allowed to store.
    The problem is that we permit writing to a page with an index _equal_ to
    the store limit - when we should reject that case.
    
    Whilst we're at it, change the triggered assertion in CacheFiles to just
    return -ENOBUFS instead.
    
    The assertion failure looks something like this:
    
    CacheFiles: Assertion failed
    1000 < 7b1 is false
    ------------[ cut here ]------------
    kernel BUG at fs/cachefiles/rdwr.c:962!
    ...
    RIP: 0010:[<ffffffffa02c9e83>]  [<ffffffffa02c9e83>] cachefiles_write_page+0x273/0x2d0 [cachefiles]
    Signed-off-by: default avatarDavid Howells <dhowells@redhat.com>
    Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
    [ kamal: backport to 3.13-stable: no __kernel_write(); thanks Ben H. ]
    Signed-off-by: default avatarKamal Mostafa <kamal@canonical.com>
    495b046a
rdwr.c 24.7 KB