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authorHannes Frederic Sowa <hannes@stressinduktion.org>2014-07-18 17:26:41 -0400
committerTheodore Ts'o <tytso@mit.edu>2014-07-19 01:42:13 -0400
commit79a8468747c5f95ed3d5ce8376a3e82e0c5857fc (patch)
treec84aca1e2222c1966b62bd87f9b702f7782b8f9c
parent1795cd9b3a91d4b5473c97f491d63892442212ab (diff)
downloadlinux-stericsson-79a8468747c5f95ed3d5ce8376a3e82e0c5857fc.tar.gz
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: Dave Jones <davej@redhat.com> Signed-off-by: Hannes Frederic Sowa <hannes@stressinduktion.org> Signed-off-by: Theodore Ts'o <tytso@mit.edu> Cc: stable@vger.kernel.org
-rw-r--r--drivers/char/random.c17
1 files changed, 14 insertions, 3 deletions
diff --git a/drivers/char/random.c b/drivers/char/random.c
index 0a7ac0a7b252..71529e196b84 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -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),