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| H A D | random.c | diff 8b76f46a2db29407fed66cf4aca19d61b3dcb3e1 Tue Sep 02 23:36:14 CEST 2008 Andrew Morton <akpm@linux-foundation.org> drivers/char/random.c: fix a race which can lead to a bogus BUG()
Fix a bug reported by and diagnosed by Aaron Straus.
This is a regression intruduced into 2.6.26 by
commit adc782dae6c4c0f6fb679a48a544cfbcd79ae3dc
Author: Matt Mackall <mpm@selenic.com>
Date: Tue Apr 29 01:03:07 2008 -0700
random: simplify and rename credit_entropy_store
credit_entropy_bits() does:
spin_lock_irqsave(&r->lock, flags);
...
if (r->entropy_count > r->poolinfo->POOLBITS)
r->entropy_count = r->poolinfo->POOLBITS;
so there is a time window in which this BUG_ON():
static size_t account(struct entropy_store *r, size_t nbytes, int min,
int reserved)
{
unsigned long flags;
BUG_ON(r->entropy_count > r->poolinfo->POOLBITS);
/* Hold lock while accounting */
spin_lock_irqsave(&r->lock, flags);
can trigger.
We could fix this by moving the assertion inside the lock, but it seems
safer and saner to revert to the old behaviour wherein
entropy_store.entropy_count at no time exceeds
entropy_store.poolinfo->POOLBITS.
Reported-by: Aaron Straus <aaron@merfinllc.com>
Cc: Matt Mackall <mpm@selenic.com>
Cc: Theodore Ts'o <tytso@mit.edu>
Cc: <stable@kernel.org> [2.6.26.x]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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