On Thu, Aug 22, 2019 at 06:59:25PM +0900, Tetsuo Handa wrote: > Tetsuo Handa wrote: > > Greg Kroah-Hartman wrote: > > > Oh, nice! This shouldn't break anything that is assuming that the read > > > will complete before a signal is delivered, right? > > > > > > I know userspace handling of "short" reads is almost always not there... > > > > Since this check will give up upon SIGKILL, userspace won't be able to see > > the return value from read(). Thus, returning 0 upon SIGKILL will be safe. > > ;-) > > Maybe we also want to add cond_resched()... > > > > By the way, do we want similar check on write_mem() side? > > If aborting "write to /dev/mem" upon SIGKILL (results in partial write) is > > unexpected, we might want to ignore SIGKILL for write_mem() case. > > But copying data from killed threads (especially when killed by OOM killer > > and userspace memory is reclaimed by OOM reaper before write_mem() returns) > > would be after all unexpected. Then, it might be preferable to check SIGKILL > > on write_mem() side... > > > > Ha, ha. syzbot reported the same problem using write_mem(). > https://syzkaller.appspot.com/text?tag=CrashLog&x=1018055a600000 > We want fatal_signal_pending() check on both sides.
Ok, want to send a patch for that? And does anything use /dev/mem anymore? I think X stopped using it a long time ago. > By the way, write_mem() worries me whether there is possibility of replacing > kernel code/data with user-defined memory data supplied from userspace. > If write_mem() were by chance replaced with code that does > > while (1); > > we won't be able to return from write_mem() even if we added > fatal_signal_pending() check. > Ditto for replacing local variables with unexpected values... I'm sorry, I don't really understand what you mean here, but I haven't had my morning coffee... Any hints as to an example? thanks, greg k-h