George Spelvin 81d7c56d6f random32: make prandom_u32() output unpredictable ... commit c51f8f88d7 upstream. Non-cryptographic PRNGs may have great statistical properties, but are usually trivially predictable to someone who knows the algorithm, given a small sample of their output. An LFSR like prandom_u32() is particularly simple, even if the sample is widely scattered bits. It turns out the network stack uses prandom_u32() for some things like random port numbers which it would prefer are *not* trivially predictable. Predictability led to a practical DNS spoofing attack. Oops. This patch replaces the LFSR with a homebrew cryptographic PRNG based on the SipHash round function, which is in turn seeded with 128 bits of strong random key. (The authors of SipHash have *not* been consulted about this abuse of their algorithm.) Speed is prioritized over security; attacks are rare, while performance is always wanted. Replacing all callers of prandom_u32() is the quick fix. Whether to reinstate a weaker PRNG for uses which can tolerate it is an open question. Commit f227e3ec3b ("random32: update the net random state on interrupt and activity") was an earlier attempt at a solution. This patch replaces it. Reported-by: Amit Klein <aksecurity@gmail.com> Cc: Willy Tarreau <w@1wt.eu> Cc: Eric Dumazet <edumazet@google.com> Cc: "Jason A. Donenfeld" <Jason@zx2c4.com> Cc: Andy Lutomirski <luto@kernel.org> Cc: Kees Cook <keescook@chromium.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: tytso@mit.edu Cc: Florian Westphal <fw@strlen.de> Cc: Marc Plumb <lkml.mplumb@gmail.com> Fixes: f227e3ec3b ("random32: update the net random state on interrupt and activity") Signed-off-by: George Spelvin <lkml@sdf.org> Link: https://lore.kernel.org/netdev/20200808152628.GA27941@SDF.ORG/ [ willy: partial reversal of f227e3ec3b5c; moved SIPROUND definitions to prandom.h for later use; merged George's prandom_seed() proposal; inlined siprand_u32(); replaced the net_rand_state[] array with 4 members to fix a build issue; cosmetic cleanups to make checkpatch happy; fixed RANDOM32_SELFTEST build ] [wt: backported to 4.19 -- various context adjustments] Signed-off-by: Willy Tarreau <w@1wt.eu> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>		2020-11-18 19:18:52 +01:00
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alarmtimer.c
clockevents.c
clocksource.c	clocksource: Prevent double add_timer_on() for watchdog_timer	2020-02-11 04:34:18 -08:00
hrtimer.c
itimer.c	time: Prevent undefined behaviour in timespec64_to_ns()	2020-11-18 19:18:40 +01:00
jiffies.c
Kconfig
Makefile
ntp_internal.h
ntp.c
posix-clock.c
posix-cpu-timers.c
posix-stubs.c
posix-timers.c
posix-timers.h
sched_clock.c
test_udelay.c
tick-broadcast-hrtimer.c
tick-broadcast.c
tick-common.c	tick/common: Touch watchdog in tick_unfreeze() on all CPUs	2020-11-18 19:18:46 +01:00
tick-internal.h
tick-oneshot.c
tick-sched.c
tick-sched.h
time.c
timeconst.bc
timeconv.c
timecounter.c
timekeeping_debug.c
timekeeping_internal.h
timekeeping.c	timekeeping: Prevent 32bit truncation in scale64_check_overflow()	2020-10-01 13:14:36 +02:00
timekeeping.h
timer_list.c
timer.c	random32: make prandom_u32() output unpredictable	2020-11-18 19:18:52 +01:00