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    SubjectRe: [linux-next PATCH] rapidio: Fix error handling path
    On Wed, Sep 16, 2020 at 01:02:32PM +0300, Dan Carpenter wrote:
    > On Wed, Sep 16, 2020 at 09:12:17AM +0530, Souptick Joarder wrote:
    > > There is an error when pin_user_pages_fast() returns -ERRNO and
    > > inside error handling path driver end up calling unpin_user_pages()
    > > with -ERRNO which is not correct.
    > >
    > > This patch will fix the problem.
    >
    > There are a few ways we could prevent bug in the future.
    >
    > 1) This could have been caught with existing static analysis tools
    > which warn about when a value is set but not used.
    >
    > 2) I've created a Smatch check which warngs about:
    >
    > drivers/rapidio/devices/rio_mport_cdev.c:955 rio_dma_transfer() warn: unpinning negative pages 'nr_pages'
    >
    > I'll test it out tonight and see how well it works. I don't
    > immediately see any other bugs allthough Smatch doesn't like the code
    > in siw_umem_release(). It uses "min_t(int" which suggests that
    > negative pages are okay.
    >
    > int to_free = min_t(int, PAGES_PER_CHUNK, num_pages);
    >
    > 3) We could add a check in unpin_user_pages().
    >
    > if (WARN_ON(IS_ERR_VALUE(npages)))
    > return;

    Does IS_ERR_VALUE() work on an unsigned variable? The issue with adding a
    check in unpin_user_pages() is that npages is unsigned long.

    Ira

    >
    > It's not possible to pin more than "ULONG_MAX - 4095" because otherwise
    > returning error pointers wouldn't work. So this check can't break
    > anything and it could prevent a crash.
    >
    > regards,
    > dan carpenter
    >

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