On Tue, Jun 20, 2017 at 3:33 PM, Theodore Ts'o <tytso@xxxxxxx> wrote: > On Mon, Jun 19, 2017 at 10:57:18PM +0200, Jason A. Donenfeld wrote: >> >> With rc6 already released and rc7 coming up, I'd really appreciate you >> stepping in here and either ACKing the above commit, or giving your >> two cents about it in case I need to roll something different. > > I actually had set up an earlier version of your patch for on Saturday > while I was in Beijing. (Like Linus, I'm attending the LinuxCon China > conference Monday and Tuesday.) I had even created the signed tag, > but I didn't send the pull request to Linus because I was waiting to > see about how discussions over the locking strategy and the spammy log > messages on PowerPC was going to get resolved. > > I've since respun the commit to reflect your newer patch (see the > random_for_linus_stable tag on random.git) and rebased the dev branch > on top of that. Please take a look and comment. > > The other open issue I want to resolve before sending a pull request > this week is whether we want to change the default for > CONFIG_WARN_UNSEEDED_RANDOM so that the answer is 'n'. It *is* spammy > for PowerPC, because they aren't getting their CRNG initialized > quickly enough, so several userspace processes are getting > fork/exec'ed with an uninitialized CRNG. It's very spammy for ARM as well. I booted next-20170619 on an Aspeed (32-bit ARM) board and by the time I made it to a shell the log buffer contained only warnings: [ 10.452921] random: arch_pick_mmap_layout+0xa8/0xe8 get_random_u32 called with crng_init=0 [ 10.461255] random: load_elf_binary+0x3c8/0x104c get_random_u32 called with crng_init=0 [ 10.471464] random: arch_setup_additional_pages+0x6c/0x110 get_random_u32 called with crng_init=0 [ 10.480429] random: randomize_page+0x44/0x58 get_random_u32 called with crng_init=0 [ 10.494802] random: arch_pick_mmap_layout+0xa8/0xe8 get_random_u32 called with crng_init=0 [ 10.503141] random: load_elf_binary+0x3c8/0x104c get_random_u32 called with crng_init=0 [ 10.511571] random: arch_setup_additional_pages+0x6c/0x110 get_random_u32 called with crng_init=0 [ 10.520527] random: randomize_page+0x44/0x58 get_random_u32 called with crng_init=0 [ 10.537847] random: arch_pick_mmap_layout+0xa8/0xe8 get_random_u32 called with crng_init=0 [ 10.546182] random: load_elf_binary+0x3c8/0x104c get_random_u32 called with crng_init=0 [ 10.554611] random: arch_setup_additional_pages+0x6c/0x110 get_random_u32 called with crng_init=0 [ 10.563563] random: randomize_page+0x44/0x58 get_random_u32 called with crng_init=0 So +1 for defaulting CONFIG_WARN_UNSEEDED_RANDOM=n. Cheers, Joel > That being said, it is a > valid warning because it means that the initial stack canary for the > first couple of PowerPC processes are being created without a fully > initialized CRNG, which may mean that an attacker might be able to > circumvent the stack canary on the first couple of processes. So that > could potentially be a real security issue on Power. OTOH, most Power > users aren't going to be able to do anything about the fact the stack > canaries of the system daemons started during early boot don't have > strong randomness, so perhaps we should disable the warning by > default. > > Opinions? > > - Ted
