[PATCH 5.5 006/367] net_sched: fix an OOB access in cls_tcindex

Greg Kroah-Hartman
2020-02-10T13:09:09Z

From: Cong Wang <xiyou.wangcong@gmail.com>

[ Upstream commit 599be01ee567b61f4471ee8078870847d0a11e8e ]

As Eric noticed, tcindex_alloc_perfect_hash() uses cp->hash
to compute the size of memory allocation, but cp->hash is
set again after the allocation, this caused an out-of-bound
access.

So we have to move all cp->hash initialization and computation
before the memory allocation. Move cp->mask and cp->shift together
as cp->hash may need them for computation too.

Reported-and-tested-by: syzbot+35d4dea36c387813ed31@syzkaller.appspotmail.com
Fixes: 331b72922c5f ("net: sched: RCU cls_tcindex")
Cc: Eric Dumazet <eric.dumazet@gmail.com>
Cc: John Fastabend <john.fastabend@gmail.com>
Cc: Jamal Hadi Salim <jhs@mojatatu.com>
Cc: Jiri Pirko <jiri@resnulli.us>
Cc: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/sched/cls_tcindex.c | 40 ++++++++++++++++++++--------------------
1 file changed, 20 insertions(+), 20 deletions(-)

--- a/net/sched/cls_tcindex.c
+++ b/net/sched/cls_tcindex.c
@@ -333,12 +333,31 @@ tcindex_set_parms(struct net *net, struc
cp->fall_through = p->fall_through;
cp->tp = tp;

+ if (tb[TCA_TCINDEX_HASH])
+ cp->hash = nla_get_u32(tb[TCA_TCINDEX_HASH]);
+
+ if (tb[TCA_TCINDEX_MASK])
+ cp->mask = nla_get_u16(tb[TCA_TCINDEX_MASK]);
+
+ if (tb[TCA_TCINDEX_SHIFT])
+ cp->shift = nla_get_u32(tb[TCA_TCINDEX_SHIFT]);
+
+ if (!cp->hash) {
+ /* Hash not specified, use perfect hash if the upper limit
+ * of the hashing index is below the threshold.
+ */
+ if ((cp->mask >> cp->shift) < PERFECT_HASH_THRESHOLD)
+ cp->hash = (cp->mask >> cp->shift) + 1;
+ else
+ cp->hash = DEFAULT_HASH_SIZE;
+ }
+
if (p->perfect) {
int i;

if (tcindex_alloc_perfect_hash(net, cp) < 0)
goto errout;
- for (i = 0; i < cp->hash; i++)
+ for (i = 0; i < min(cp->hash, p->hash); i++)
cp->perfect[i].res = p->perfect[i].res;
balloc = 1;
}
@@ -350,15 +369,6 @@ tcindex_set_parms(struct net *net, struc
if (old_r)
cr = r->res;

- if (tb[TCA_TCINDEX_HASH])
- cp->hash = nla_get_u32(tb[TCA_TCINDEX_HASH]);
-
- if (tb[TCA_TCINDEX_MASK])
- cp->mask = nla_get_u16(tb[TCA_TCINDEX_MASK]);
-
- if (tb[TCA_TCINDEX_SHIFT])
- cp->shift = nla_get_u32(tb[TCA_TCINDEX_SHIFT]);
-
err = -EBUSY;

/* Hash already allocated, make sure that we still meet the
@@ -376,16 +386,6 @@ tcindex_set_parms(struct net *net, struc
if (tb[TCA_TCINDEX_FALL_THROUGH])
cp->fall_through = nla_get_u32(tb[TCA_TCINDEX_FALL_THROUGH]);

- if (!cp->hash) {
- /* Hash not specified, use perfect hash if the upper limit
- * of the hashing index is below the threshold.
- */
- if ((cp->mask >> cp->shift) < PERFECT_HASH_THRESHOLD)
- cp->hash = (cp->mask >> cp->shift) + 1;
- else
- cp->hash = DEFAULT_HASH_SIZE;
- }
-
if (!cp->perfect && !cp->h)
cp->alloc_hash = cp->hash;