[2.6.20.17 review 50/58] random: fix bound check ordering (CVE-2007-3105)

Willy Tarreau
2007-08-22T09:11:20Z

[-- Attachment #1: 0050-random-fix-bound-check-ordering-CVE-2007-3105.patch --]
[-- Type: text/plain, Size: 1480 bytes --]

If root raised the default wakeup threshold over the size of the
output pool, the pool transfer function could overflow the stack with
RNG bytes, causing a DoS or potential privilege escalation.

(Bug reported by the PaX Team <pageexec@freemail.hu>)

Cc: Theodore Tso <tytso@mit.edu>
Cc: Willy Tarreau <w@1wt.eu>
Signed-off-by: Matt Mackall <mpm@selenic.com>
Signed-off-by: Chris Wright <chrisw@sous-sol.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Signed-off-by: Willy Tarreau <w@1wt.eu>
---
drivers/char/random.c | 9 +++++++--
1 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/drivers/char/random.c b/drivers/char/random.c
index 263e5e5..96561c8 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -693,9 +693,14 @@ static void xfer_secondary_pool(struct entropy_store *r, size_t nbytes)

if (r->pull && r->entropy_count < nbytes * 8 &&
r->entropy_count < r->poolinfo->POOLBITS) {
- int bytes = max_t(int, random_read_wakeup_thresh / 8,
- min_t(int, nbytes, sizeof(tmp)));
+ /* If we're limited, always leave two wakeup worth's BITS */
int rsvd = r->limit ? 0 : random_read_wakeup_thresh/4;
+ int bytes = nbytes;
+
+ /* pull at least as many as BYTES as wakeup BITS */
+ bytes = max_t(int, bytes, random_read_wakeup_thresh / 8);
+ /* but never more than the buffer size */
+ bytes = min_t(int, bytes, sizeof(tmp));

DEBUG_ENT("going to reseed %s with %d bits "
"(%d of %d requested)
",
--
1.5.2.5

--