• David Howells's avatar
    assoc_array: Fix a buggy node-splitting case · ea678998
    David Howells authored
    This fixes CVE-2017-12193.
    
    Fix a case in the assoc_array implementation in which a new leaf is
    added that needs to go into a node that happens to be full, where the
    existing leaves in that node cluster together at that level to the
    exclusion of new leaf.
    
    What needs to happen is that the existing leaves get moved out to a new
    node, N1, at level + 1 and the existing node needs replacing with one,
    N0, that has pointers to the new leaf and to N1.
    
    The code that tries to do this gets this wrong in two ways:
    
     (1) The pointer that should've pointed from N0 to N1 is set to point
         recursively to N0 instead.
    
     (2) The backpointer from N0 needs to be set correctly in the case N0 is
         either the root node or reached through a shortcut.
    
    Fix this by removing this path and using the split_node path instead,
    which achieves the same end, but in a more general way (thanks to Eric
    Biggers for spotting the redundancy).
    
    The problem manifests itself as:
    
      BUG: unable to handle kernel NULL pointer dereference at 0000000000000010
      IP: assoc_array_apply_edit+0x59/0xe5
    
    Fixes: 3cb98950 ("Add a generic associative array implementation.")
    Reported-and-tested-by: 's avatarWU Fan <u3536072@connect.hku.hk>
    Signed-off-by: 's avatarDavid Howells <dhowells@redhat.com>
    Cc: stable@vger.kernel.org [v3.13-rc1+]
    Signed-off-by: 's avatarLinus Torvalds <torvalds@linux-foundation.org>
    ea678998
assoc_array.c 52 KB