Messages in this thread | | | Date | Thu, 21 Sep 2017 04:26:05 +0100 | From | Al Viro <> | Subject | Re: [PATCH] mpt3sas: downgrade full copy_from_user to access_ok check |
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On Tue, Sep 19, 2017 at 11:11:11PM -0400, Meng Xu wrote: > Since right after the user copy, we are going to > memset(&karg, 0, sizeof(karg)), I guess an access_ok check is enough?
access_ok() is *NOT* "will copy_from_user() succeed?" Not even close. On a bunch of architectures (sparc64, for one) access_ok() is always true.
All it does is checking that address is not a kernel one - e.g. on i386 anything in range 0..3Gb qualifies. Whether anything's mapped at that address or not.
Why bother with that copy_from_user() at all? The same ioctl() proceeds to copy_to_user() on exact same range; all you get from it is "if the area passed by caller is writable, but not readable, fail with -EFAULT". Who cares?
Just drop that copy_from_user() completely. Anything access_ok() might've caught will be caught by copy_to_user() anyway.
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