Messages in this thread | | | Date | Wed, 9 Dec 2015 17:21:30 -0800 | From | Christoph Hellwig <> | Subject | Re: [PATCH v5] fs: clear file privilege bits when mmap writing |
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> Changing the bits requires holding inode->i_mutex, so it cannot be done > during the page fault (due to mmap_sem being held during the fault). We > could do this during vm_mmap_pgoff, but that would need coverage in > mprotect as well, but to check for MAP_SHARED, we'd need to hold mmap_sem > again. We could clear at open() time, but it's possible things are > accidentally opening with O_RDWR and only reading. Better to clear on > close and error failures (i.e. an improvement over now, which is not > clearing at all). > > Instead, detect the need to clear the bits during the page fault, and > actually remove the bits during final fput. Since the file was open for > writing, it wouldn't have been possible to execute it yet.
> > Signed-off-by: Kees Cook <keescook@chromium.org> > --- > I think this is the best we can do; everything else is blocked by mmap_sem.
It should be done at mmap time, before even taking mmap_sem.
Adding a new field for this to strut file isn't really acceptable.
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