Messages in this thread |  | | From | Linus Torvalds <> | Date | Sat, 1 Jun 2019 09:14:17 -0700 | Subject | Re: [PATCH 03/16] mm: simplify gup_fast_permitted |
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On Sat, Jun 1, 2019 at 12:50 AM Christoph Hellwig <hch@lst.de> wrote: > > Pass in the already calculated end value instead of recomputing it, and > leave the end > start check in the callers instead of duplicating them > in the arch code.
Good cleanup, except it's wrong.
> - if (nr_pages <= 0) > + if (end < start) > return 0;
You moved the overflow test to generic code - good.
You removed the sign and zero test on nr_pages - bad.
The zero test in particular is _important_ - the GUP range operators know and depend on the fact that they are passed a non-empty range.
The sign test it less so, but is definitely appropriate. It might be even better to check that the "<< PAGE_SHIFT" doesn't overflow in "long", of course, but with callers being supposed to be trusted, the sign test at least checks for stupid underflow issues.
So at the very least that "(end < start)" needs to be "(end <= start)", but honestly, I think the sign of the nr_pages should be continued to be checked.
Linus
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