Commit 79a84687 authored by Hannes Frederic Sowa's avatar Hannes Frederic Sowa Committed by Theodore Ts'o
Browse files

random: check for increase of entropy_count because of signed conversion 



The expression entropy_count -= ibytes << (ENTROPY_SHIFT + 3) could
actually increase entropy_count if during assignment of the unsigned
expression on the RHS (mind the -=) we reduce the value modulo
2^width(int) and assign it to entropy_count. Trinity found this.

[ Commit modified by tytso to add an additional safety check for a
  negative entropy_count -- which should never happen, and to also add
  an additional paranoia check to prevent overly large count values to
  be passed into urandom_read().  ]

Reported-by: default avatarDave Jones <davej@redhat.com>
Signed-off-by: default avatarHannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: default avatarTheodore Ts'o <tytso@mit.edu>
Cc: stable@vger.kernel.org
parent 1795cd9b

drivers/char/random.c

+14 −3
Original line number Diff line number Diff line
@@ -641,7 +641,7 @@ retry: 
		} while (unlikely(entropy_count < pool_size-2 && pnfrac));

	}



	if (entropy_count < 0) {

	if (unlikely(entropy_count < 0)) {

		pr_warn("random: negative entropy/overflow: pool %s count %d\n",

			r->name, entropy_count);

		WARN_ON(1);
@@ -981,7 +981,7 @@ static size_t account(struct entropy_store *r, size_t nbytes, int min, 
		      int reserved)

{

	int entropy_count, orig;

	size_t ibytes;

	size_t ibytes, nfrac;



	BUG_ON(r->entropy_count > r->poolinfo->poolfracbits);
@@ -999,7 +999,17 @@ retry: 
	}

	if (ibytes < min)

		ibytes = 0;

	if ((entropy_count -= ibytes << (ENTROPY_SHIFT + 3)) < 0)



	if (unlikely(entropy_count < 0)) {

		pr_warn("random: negative entropy count: pool %s count %d\n",

			r->name, entropy_count);

		WARN_ON(1);

		entropy_count = 0;

	}

	nfrac = ibytes << (ENTROPY_SHIFT + 3);

	if ((size_t) entropy_count > nfrac)

		entropy_count -= nfrac;

	else

		entropy_count = 0;



	if (cmpxchg(&r->entropy_count, orig, entropy_count) != orig)
@@ -1376,6 +1386,7 @@ urandom_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos) 
			    "with %d bits of entropy available\n",

			    current->comm, nonblocking_pool.entropy_total);



	nbytes = min_t(size_t, nbytes, INT_MAX >> (ENTROPY_SHIFT + 3));

	ret = extract_entropy_user(&nonblocking_pool, buf, nbytes);



	trace_urandom_read(8 * nbytes, ENTROPY_BITS(&nonblocking_pool),

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