From 1e7e2e05c179a68aaf8830fe91547a87f4589e53 Mon Sep 17 00:00:00 2001 From: Jarod Wilson Date: Fri, 24 May 2013 15:55:31 -0700 Subject: drivers/char/random.c: fix priming of last_data Commit ec8f02da9ea5 ("random: prime last_data value per fips requirements") added priming of last_data per fips requirements. Unfortuantely, it did so in a way that can lead to multiple threads all incrementing nbytes, but only one actually doing anything with the extra data, which leads to some fun random corruption and panics. The fix is to simply do everything needed to prime last_data in a single shot, so there's no window for multiple cpus to increment nbytes -- in fact, we won't even increment or decrement nbytes anymore, we'll just extract the needed EXTRACT_SIZE one time per pool and then carry on with the normal routine. All these changes have been tested across multiple hosts and architectures where panics were previously encoutered. The code changes are are strictly limited to areas only touched when when booted in fips mode. This change should also go into 3.8-stable, to make the myriads of fips users on 3.8.x happy. Signed-off-by: Jarod Wilson Tested-by: Jan Stancek Tested-by: Jan Stodola Cc: Herbert Xu Acked-by: Neil Horman Cc: "David S. Miller" Cc: Matt Mackall Cc: "Theodore Ts'o" Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- drivers/char/random.c | 30 +++++++++++++++--------------- 1 file changed, 15 insertions(+), 15 deletions(-) (limited to 'drivers/char') diff --git a/drivers/char/random.c b/drivers/char/random.c index cd9a6211dcad..73e52b7796f9 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -957,10 +957,23 @@ static ssize_t extract_entropy(struct entropy_store *r, void *buf, { ssize_t ret = 0, i; __u8 tmp[EXTRACT_SIZE]; + unsigned long flags; /* if last_data isn't primed, we need EXTRACT_SIZE extra bytes */ - if (fips_enabled && !r->last_data_init) - nbytes += EXTRACT_SIZE; + if (fips_enabled) { + spin_lock_irqsave(&r->lock, flags); + if (!r->last_data_init) { + r->last_data_init = true; + spin_unlock_irqrestore(&r->lock, flags); + trace_extract_entropy(r->name, EXTRACT_SIZE, + r->entropy_count, _RET_IP_); + xfer_secondary_pool(r, EXTRACT_SIZE); + extract_buf(r, tmp); + spin_lock_irqsave(&r->lock, flags); + memcpy(r->last_data, tmp, EXTRACT_SIZE); + } + spin_unlock_irqrestore(&r->lock, flags); + } trace_extract_entropy(r->name, nbytes, r->entropy_count, _RET_IP_); xfer_secondary_pool(r, nbytes); @@ -970,19 +983,6 @@ static ssize_t extract_entropy(struct entropy_store *r, void *buf, extract_buf(r, tmp); if (fips_enabled) { - unsigned long flags; - - - /* prime last_data value if need be, per fips 140-2 */ - if (!r->last_data_init) { - spin_lock_irqsave(&r->lock, flags); - memcpy(r->last_data, tmp, EXTRACT_SIZE); - r->last_data_init = true; - nbytes -= EXTRACT_SIZE; - spin_unlock_irqrestore(&r->lock, flags); - extract_buf(r, tmp); - } - spin_lock_irqsave(&r->lock, flags); if (!memcmp(tmp, r->last_data, EXTRACT_SIZE)) panic("Hardware RNG duplicated output!\n"); -- cgit v1.2.3 From 10b3a32d292c21ea5b3ad5ca5975e88bb20b8d68 Mon Sep 17 00:00:00 2001 From: Jiri Kosina Date: Fri, 24 May 2013 15:55:33 -0700 Subject: random: fix accounting race condition with lockless irq entropy_count update Commit 902c098a3663 ("random: use lockless techniques in the interrupt path") turned IRQ path from being spinlock protected into lockless cmpxchg-retry update. That commit removed r->lock serialization between crediting entropy bits from IRQ context and accounting when extracting entropy on userspace read path, but didn't turn the r->entropy_count reads/updates in account() to use cmpxchg as well. It has been observed, that under certain circumstances this leads to read() on /dev/urandom to return 0 (EOF), as r->entropy_count gets corrupted and becomes negative, which in turn results in propagating 0 all the way from account() to the actual read() call. Convert the accounting code to be the proper lockless counterpart of what has been partially done by 902c098a3663. Signed-off-by: Jiri Kosina Cc: Theodore Ts'o Cc: Greg KH Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- drivers/char/random.c | 24 ++++++++++++++++-------- 1 file changed, 16 insertions(+), 8 deletions(-) (limited to 'drivers/char') diff --git a/drivers/char/random.c b/drivers/char/random.c index 73e52b7796f9..35487e8ded59 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -865,16 +865,24 @@ static size_t account(struct entropy_store *r, size_t nbytes, int min, if (r->entropy_count / 8 < min + reserved) { nbytes = 0; } else { + int entropy_count, orig; +retry: + entropy_count = orig = ACCESS_ONCE(r->entropy_count); /* If limited, never pull more than available */ - if (r->limit && nbytes + reserved >= r->entropy_count / 8) - nbytes = r->entropy_count/8 - reserved; - - if (r->entropy_count / 8 >= nbytes + reserved) - r->entropy_count -= nbytes*8; - else - r->entropy_count = reserved; + if (r->limit && nbytes + reserved >= entropy_count / 8) + nbytes = entropy_count/8 - reserved; + + if (entropy_count / 8 >= nbytes + reserved) { + entropy_count -= nbytes*8; + if (cmpxchg(&r->entropy_count, orig, entropy_count) != orig) + goto retry; + } else { + entropy_count = reserved; + if (cmpxchg(&r->entropy_count, orig, entropy_count) != orig) + goto retry; + } - if (r->entropy_count < random_write_wakeup_thresh) + if (entropy_count < random_write_wakeup_thresh) wakeup_write = 1; } -- cgit v1.2.3