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

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
...@@ -641,7 +641,7 @@ static void credit_entropy_bits(struct entropy_store *r, int nbits) ...@@ -641,7 +641,7 @@ static void credit_entropy_bits(struct entropy_store *r, int nbits)
} while (unlikely(entropy_count < pool_size-2 && pnfrac)); } 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", pr_warn("random: negative entropy/overflow: pool %s count %d\n",
r->name, entropy_count); r->name, entropy_count);
WARN_ON(1); WARN_ON(1);
...@@ -981,7 +981,7 @@ static size_t account(struct entropy_store *r, size_t nbytes, int min, ...@@ -981,7 +981,7 @@ static size_t account(struct entropy_store *r, size_t nbytes, int min,
int reserved) int reserved)
{ {
int entropy_count, orig; int entropy_count, orig;
size_t ibytes; size_t ibytes, nfrac;
BUG_ON(r->entropy_count > r->poolinfo->poolfracbits); BUG_ON(r->entropy_count > r->poolinfo->poolfracbits);
...@@ -999,7 +999,17 @@ static size_t account(struct entropy_store *r, size_t nbytes, int min, ...@@ -999,7 +999,17 @@ static size_t account(struct entropy_store *r, size_t nbytes, int min,
} }
if (ibytes < min) if (ibytes < min)
ibytes = 0; 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; entropy_count = 0;
if (cmpxchg(&r->entropy_count, orig, entropy_count) != orig) 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) ...@@ -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", "with %d bits of entropy available\n",
current->comm, nonblocking_pool.entropy_total); 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); ret = extract_entropy_user(&nonblocking_pool, buf, nbytes);
trace_urandom_read(8 * nbytes, ENTROPY_BITS(&nonblocking_pool), trace_urandom_read(8 * nbytes, ENTROPY_BITS(&nonblocking_pool),
......
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