Messages in this thread | | | Date | Mon, 8 Dec 2014 18:35:42 +0000 | From | Al Viro <> | Subject | Re: [RFC][PATCHES] iov_iter.c rewrite |
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On Mon, Dec 08, 2014 at 10:23:26AM -0800, Linus Torvalds wrote:
> Did this actually use to work? Or is it an issue of "the new iov_iter > is so generic that something that used to just return an error now > 'works' and triggers the problem"?
Looks like it failed with EINVAL. Which might very well be the sane reaction - if we run into a vmalloc/module address, act as if we failed to get that page and exit the loop.
> > What's the sane way to grab struct page * for a vmalloc'ed address? > > So "vmalloc_to_page()" should work. > > However, it's actually fundamentally racy unless you can guarantee > that the vmalloc()'ed area in question is stable (so you had better > have done that allocation yourself, and be in control of the freeing, > rather than "we look up random vmalloc'ed addresses).
If vfree(buffer) races with kernel_read() into buffer, we are so badly fucked that stability of pointers to pages is the least of our concerns...
> In general, it's really a horrible thing to use, and tends to be a big > red sign that "somebody misdesigned this badly"
More like "nobody has thought of that case", at a guess, but then I hadn't been involved in finit_module() design - I don't even remember the discussions around it. That would be what, something circa 3.7?
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