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random: fix entropy accounting bug introduced in v3.15

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Merge tag 'random_for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tytso/random

Pull randomness bugfix from Ted Ts'o:
 "random: fix entropy accounting bug introduced in v3.15"

* tag 'random_for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tytso/random:
  random: fix nasty entropy accounting bug
This commit is contained in:
Linus Torvalds 2014-06-17 14:23:14 -10:00
commit 5ee22beeb2
1 changed files with 9 additions and 8 deletions
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17
drivers/char/random.c
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@ -980,7 +980,6 @@ static void push_to_pool(struct work_struct *work)
static size_t account(struct entropy_store *r, size_t nbytes, int min,
int reserved)
{
int have_bytes;
int entropy_count, orig;
size_t ibytes;
@ -989,17 +988,19 @@ static size_t account(struct entropy_store *r, size_t nbytes, int min,
/* Can we pull enough? */
retry:
entropy_count = orig = ACCESS_ONCE(r->entropy_count);
have_bytes = entropy_count >> (ENTROPY_SHIFT + 3);
ibytes = nbytes;
/* If limited, never pull more than available */
if (r->limit)
ibytes = min_t(size_t, ibytes, have_bytes - reserved);
if (r->limit) {
int have_bytes = entropy_count >> (ENTROPY_SHIFT + 3);
if ((have_bytes -= reserved) < 0)
have_bytes = 0;
ibytes = min_t(size_t, ibytes, have_bytes);
}
if (ibytes < min)
ibytes = 0;
if (have_bytes >= ibytes + reserved)
entropy_count -= ibytes << (ENTROPY_SHIFT + 3);
else
entropy_count = reserved << (ENTROPY_SHIFT + 3);
if ((entropy_count -= ibytes << (ENTROPY_SHIFT + 3)) < 0)
entropy_count = 0;
if (cmpxchg(&r->entropy_count, orig, entropy_count) != orig)
goto retry;