• Wenwen Wang's avatar
    isdn: eicon: fix a missing-check bug · ebe79f9c
    Wenwen Wang authored
    [ Upstream commit 6009d1fe6ba3bb2dab55921da60465329cc1cd89 ]
    
    In divasmain.c, the function divas_write() firstly invokes the function
    diva_xdi_open_adapter() to open the adapter that matches with the adapter
    number provided by the user, and then invokes the function diva_xdi_write()
    to perform the write operation using the matched adapter. The two functions
    diva_xdi_open_adapter() and diva_xdi_write() are located in diva.c.
    
    In diva_xdi_open_adapter(), the user command is copied to the object 'msg'
    from the userspace pointer 'src' through the function pointer 'cp_fn',
    which eventually calls copy_from_user() to do the copy. Then, the adapter
    number 'msg.adapter' is used to find out a matched adapter from the
    'adapter_queue'. A matched adapter will be returned if it is found.
    Otherwise, NULL is returned to indicate the failure of the verification on
    the adapter number.
    
    As mentioned above, if a matched adapter is returned, the function
    diva_xdi_write() is invoked to perform the write operation. In this
    function, the user command is copied once again from the userspace pointer
    'src', which is the same as the 'src' pointer in diva_xdi_open_adapter() as
    both of them are from the 'buf' pointer in divas_write(). Similarly, the
    copy is achieved through the function pointer 'cp_fn', which finally calls
    copy_from_user(). After the successful copy, the corresponding command
    processing handler of the matched adapter is invoked to perform the write
    operation.
    
    It is obvious that there are two copies here from userspace, one is in
    diva_xdi_open_adapter(), and one is in diva_xdi_write(). Plus, both of
    these two copies share the same source userspace pointer, i.e., the 'buf'
    pointer in divas_write(). Given that a malicious userspace process can race
    to change the content pointed by the 'buf' pointer, this can pose potential
    security issues. For example, in the first copy, the user provides a valid
    adapter number to pass the verification process and a valid adapter can be
    found. Then the user can modify the adapter number to an invalid number.
    This way, the user can bypass the verification process of the adapter
    number and inject inconsistent data.
    
    This patch reuses the data copied in
    diva_xdi_open_adapter() and passes it to diva_xdi_write(). This way, the
    above issues can be avoided.
    Signed-off-by: 's avatarWenwen Wang <wang6495@umn.edu>
    Signed-off-by: 's avatarDavid S. Miller <davem@davemloft.net>
    Signed-off-by: 's avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
    ebe79f9c
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