On Sat, Feb 16, 2019 at 11:47:02PM +0000, Al Viro wrote: > On Sat, Feb 16, 2019 at 02:50:15PM -0800, Andy Lutomirski wrote: > > > What is the actual problem? We’re not actually demand-faulting this data, > > are we? Are we just overrunning the buffer because the from_user helpers > > are too clever? Can we fix it for real by having the fancy helpers do > > *aligned* loads so that they don’t overrun the buffer? Heck, this might be > > faster, too. > > Unaligned _stores_ are not any cheaper, and you'd get one hell of > extra arithmetics from trying to avoid both. Check something > like e.g. memcpy() on alpha, where you really have to keep all > accesses aligned, both on load and on store side. > > Can't we just pad the buffers a bit? Making sure that name_buf > and symlink_buf are _not_ followed by unmapped pages shouldn't > be hard. Both are allocated by kmalloc(), so... > > What am I missing here?
... the fact that read_info() might skip copying if everything it wants is already in the buffer passed by decompressor ;-/ It's been a while since I looked into that code...
