On Tue, Aug 18, 2020 at 12:58:07PM -0700, Kees Cook wrote: > On Tue, Aug 18, 2020 at 09:54:46PM +0200, Christoph Hellwig wrote: > > On Tue, Aug 18, 2020 at 12:39:34PM -0700, Kees Cook wrote: > > > On Mon, Aug 17, 2020 at 09:32:04AM +0200, Christoph Hellwig wrote: > > > > default_file_splice_write is the last piece of generic code that uses > > > > set_fs to make the uaccess routines operate on kernel pointers. It > > > > implements a "fallback loop" for splicing from files that do not actually > > > > provide a proper splice_read method. The usual file systems and other > > > > high bandwith instances all provide a ->splice_read, so this just removes > > > > support for various device drivers and procfs/debugfs files. If splice > > > > support for any of those turns out to be important it can be added back > > > > by switching them to the iter ops and using generic_file_splice_read. > > > > > > > > Signed-off-by: Christoph Hellwig <hch@xxxxxx> > > > > > > This seems a bit disruptive? I feel like this is going to make fuzzers > > > really noisy (e.g. trinity likes to splice random stuff out of /sys and > > > /proc). > > > > Noisy in the sence of triggering the pr_debug or because they can't > > handle -EINVAL? > > Well, maybe both? I doubt much _expects_ to be using splice, so I'm fine > with that, but it seems weird not to have a fall-back, especially if > something would like to splice a file out of there. But, I'm not opposed > to the change, it just seems like it might cause pain down the road. The problem is that without pretending a buffer is in user space when it actually isn't, we can't have a generic fallback. So we'll have to have specific support - I wrote generic support for seq_file, and willy did for /proc/sys, but at least the first caused a few problems and a fair amount of churn, so I'd rather see first if we can get away without it. > > -- > Kees Cook ---end quoted text---
