This is a note to let you know that I've just added the patch titled
random: check for increase of entropy_count because of signed conversion
to the 3.15-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
random-check-for-increase-of-entropy_count-because-of-signed-conversion.patch
and it can be found in the queue-3.15 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 79a8468747c5f95ed3d5ce8376a3e82e0c5857fc Mon Sep 17 00:00:00 2001
From: Hannes Frederic Sowa <hannes@xxxxxxxxxxxxxxxxxxx>
Date: Fri, 18 Jul 2014 17:26:41 -0400
Subject: random: check for increase of entropy_count because of signed conversion
From: Hannes Frederic Sowa <hannes@xxxxxxxxxxxxxxxxxxx>
commit 79a8468747c5f95ed3d5ce8376a3e82e0c5857fc upstream.
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@xxxxxxxxxx>
Signed-off-by: Hannes Frederic Sowa <hannes@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Theodore Ts'o <tytso@xxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/char/random.c | 17 ++++++++++++++---
1 file changed, 14 insertions(+), 3 deletions(-)
--- 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);
@@ -980,7 +980,7 @@ static size_t account(struct entropy_sto
int reserved)
{
int entropy_count, orig;
- size_t ibytes;
+ size_t ibytes, nfrac;
BUG_ON(r->entropy_count > r->poolinfo->poolfracbits);
@@ -998,7 +998,17 @@ 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)
@@ -1375,6 +1385,7 @@ urandom_read(struct file *file, char __u
"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),
Patches currently in stable-queue which might be from hannes@xxxxxxxxxxxxxxxxxxx are
queue-3.15/random-check-for-increase-of-entropy_count-because-of-signed-conversion.patch
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