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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: Wenwen Wang <wang6495@umn.edu> Signed-off-by: David S. Miller <davem@davemloft.net> |
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