timekeeping: contribute wall clock to rng on time change

[ Upstream commit aa8463e7830a273ebc04ae78270c9e596b9d3b9d ]

The rng's random_init() function contributes the real time to the rng at
boot time, so that events can at least start in relation to something
particular in the real world. But this clock might not yet be set that
point in boot, so nothing is contributed. In addition, the relation
between minor clock changes from, say, NTP, and the cycle counter is
potentially useful entropic data.

This commit addresses this by mixing in a time stamp on calls to
settimeofday and adjtimex. No entropy is credited in doing so, so it
doesn't make initialization faster, but it is still useful input to
have.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Cc: stable@vger.kernel.org
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index 871c912860ed508505c1eef9a2af7fd050fba877..d6a0ff68df410fc0432569ee4b94a47a1bc6dffc 100644 (file)
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -23,6 +23,7 @@
 #include <linux/pvclock_gtod.h>
 #include <linux/compiler.h>
 #include <linux/audit.h>
+#include <linux/random.h>
 
 #include "tick-internal.h"
 #include "ntp_internal.h"
@@ -1326,8 +1327,10 @@ out:
        /* Signal hrtimers about time change */
        clock_was_set(CLOCK_SET_WALL);
 
-       if (!ret)
+       if (!ret) {
                audit_tk_injoffset(ts_delta);
+               add_device_randomness(ts, sizeof(*ts));
+       }
 
        return ret;
 }
@@ -2413,6 +2416,7 @@ int do_adjtimex(struct __kernel_timex *txc)
        ret = timekeeping_validate_timex(txc);
        if (ret)
                return ret;
+       add_device_randomness(txc, sizeof(*txc));
 
        if (txc->modes & ADJ_SETOFFSET) {
                struct timespec64 delta;
@@ -2430,6 +2434,7 @@ int do_adjtimex(struct __kernel_timex *txc)
        audit_ntp_init(&ad);
 
        ktime_get_real_ts64(&ts);
+       add_device_randomness(&ts, sizeof(ts));
 
        raw_spin_lock_irqsave(&timekeeper_lock, flags);
        write_seqcount_begin(&tk_core.seq);