[PATCH 6.4 207/800] sch_netem: fix issues in netem_change() vs get_dist_table()

Greg Kroah-Hartman
2023-07-16T20:02:50Z

From: Eric Dumazet <edumazet@google.com>

[ Upstream commit 11b73313c12403f617b47752db0ab3deef201af7 ]

In blamed commit, I missed that get_dist_table() was allocating
memory using GFP_KERNEL, and acquiring qdisc lock to perform
the swap of newly allocated table with current one.

In this patch, get_dist_table() is allocating memory and
copy user data before we acquire the qdisc lock.

Then we perform swap operations while being protected by the lock.

Note that after this patch netem_change() no longer can do partial changes.
If an error is returned, qdisc conf is left unchanged.

Fixes: 2174a08db80d ("sch_netem: acquire qdisc lock in netem_change()")
Reported-by: syzbot <syzkaller@googlegroups.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Stephen Hemminger <stephen@networkplumber.org>
Acked-by: Jamal Hadi Salim <jhs@mojatatu.com>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Link: https://lore.kernel.org/r/20230622181503.2327695-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/sched/sch_netem.c | 59 ++++++++++++++++++-------------------------
1 file changed, 25 insertions(+), 34 deletions(-)

diff --git a/net/sched/sch_netem.c b/net/sched/sch_netem.c
index e79be1b3e74da..b93ec2a3454eb 100644
--- a/net/sched/sch_netem.c
+++ b/net/sched/sch_netem.c
@@ -773,12 +773,10 @@ static void dist_free(struct disttable *d)
* signed 16 bit values.
*/

-static int get_dist_table(struct Qdisc *sch, struct disttable **tbl,
- const struct nlattr *attr)
+static int get_dist_table(struct disttable **tbl, const struct nlattr *attr)
{
size_t n = nla_len(attr)/sizeof(__s16);
const __s16 *data = nla_data(attr);
- spinlock_t *root_lock;
struct disttable *d;
int i;

@@ -793,13 +791,7 @@ static int get_dist_table(struct Qdisc *sch, struct disttable **tbl,
for (i = 0; i < n; i++)
d->table[i] = data[i];

- root_lock = qdisc_root_sleeping_lock(sch);
-
- spin_lock_bh(root_lock);
- swap(*tbl, d);
- spin_unlock_bh(root_lock);
-
- dist_free(d);
+ *tbl = d;
return 0;
}

@@ -956,6 +948,8 @@ static int netem_change(struct Qdisc *sch, struct nlattr *opt,
{
struct netem_sched_data *q = qdisc_priv(sch);
struct nlattr *tb[TCA_NETEM_MAX + 1];
+ struct disttable *delay_dist = NULL;
+ struct disttable *slot_dist = NULL;
struct tc_netem_qopt *qopt;
struct clgstate old_clg;
int old_loss_model = CLG_RANDOM;
@@ -966,6 +960,18 @@ static int netem_change(struct Qdisc *sch, struct nlattr *opt,
if (ret < 0)
return ret;

+ if (tb[TCA_NETEM_DELAY_DIST]) {
+ ret = get_dist_table(&delay_dist, tb[TCA_NETEM_DELAY_DIST]);
+ if (ret)
+ goto table_free;
+ }
+
+ if (tb[TCA_NETEM_SLOT_DIST]) {
+ ret = get_dist_table(&slot_dist, tb[TCA_NETEM_SLOT_DIST]);
+ if (ret)
+ goto table_free;
+ }
+
sch_tree_lock(sch);
/* backup q->clg and q->loss_model */
old_clg = q->clg;
@@ -975,26 +981,17 @@ static int netem_change(struct Qdisc *sch, struct nlattr *opt,
ret = get_loss_clg(q, tb[TCA_NETEM_LOSS]);
if (ret) {
q->loss_model = old_loss_model;
+ q->clg = old_clg;
goto unlock;
}
} else {
q->loss_model = CLG_RANDOM;
}

- if (tb[TCA_NETEM_DELAY_DIST]) {
- ret = get_dist_table(sch, &q->delay_dist,
- tb[TCA_NETEM_DELAY_DIST]);
- if (ret)
- goto get_table_failure;
- }
-
- if (tb[TCA_NETEM_SLOT_DIST]) {
- ret = get_dist_table(sch, &q->slot_dist,
- tb[TCA_NETEM_SLOT_DIST]);
- if (ret)
- goto get_table_failure;
- }
-
+ if (delay_dist)
+ swap(q->delay_dist, delay_dist);
+ if (slot_dist)
+ swap(q->slot_dist, slot_dist);
sch->limit = qopt->limit;

q->latency = PSCHED_TICKS2NS(qopt->latency);
@@ -1044,17 +1041,11 @@ static int netem_change(struct Qdisc *sch, struct nlattr *opt,

unlock:
sch_tree_unlock(sch);
- return ret;

-get_table_failure:
- /* recover clg and loss_model, in case of
- * q->clg and q->loss_model were modified
- * in get_loss_clg()
- */
- q->clg = old_clg;
- q->loss_model = old_loss_model;
-
- goto unlock;
+table_free:
+ dist_free(delay_dist);
+ dist_free(slot_dist);
+ return ret;
}

static int netem_init(struct Qdisc *sch, struct nlattr *opt,
--
2.39.2