Skip to content

Commit

Permalink
net_sched: fix RTNL deadlock again caused by request_module()
Browse files Browse the repository at this point in the history 
commit d349f99 upstream.

tcf_action_init_1() loads tc action modules automatically with
request_module() after parsing the tc action names, and it drops RTNL
lock and re-holds it before and after request_module(). This causes a
lot of troubles, as discovered by syzbot, because we can be in the
middle of batch initializations when we create an array of tc actions.

One of the problem is deadlock:

CPU 0					CPU 1
rtnl_lock();
for (...) {
  tcf_action_init_1();
    -> rtnl_unlock();
    -> request_module();
				rtnl_lock();
				for (...) {
				  tcf_action_init_1();
				    -> tcf_idr_check_alloc();
				   // Insert one action into idr,
				   // but it is not committed until
				   // tcf_idr_insert_many(), then drop
				   // the RTNL lock in the _next_
				   // iteration
				   -> rtnl_unlock();
    -> rtnl_lock();
    -> a_o->init();
      -> tcf_idr_check_alloc();
      // Now waiting for the same index
      // to be committed
				    -> request_module();
				    -> rtnl_lock()
				    // Now waiting for RTNL lock
				}
				rtnl_unlock();
}
rtnl_unlock();

This is not easy to solve, we can move the request_module() before
this loop and pre-load all the modules we need for this netlink
message and then do the rest initializations. So the loop breaks down
to two now:

        for (i = 1; i <= TCA_ACT_MAX_PRIO && tb[i]; i++) {
                struct tc_action_ops *a_o;

                a_o = tc_action_load_ops(name, tb[i]...);
                ops[i - 1] = a_o;
        }

        for (i = 1; i <= TCA_ACT_MAX_PRIO && tb[i]; i++) {
                act = tcf_action_init_1(ops[i - 1]...);
        }

Although this looks serious, it only has been reported by syzbot, so it
seems hard to trigger this by humans. And given the size of this patch,
I'd suggest to make it to net-next and not to backport to stable.

This patch has been tested by syzbot and tested with tdc.py by me.

Fixes: 0fedc63 ("net_sched: commit action insertions together")
Reported-and-tested-by: syzbot+82752bc5331601cf4899@syzkaller.appspotmail.com
Reported-and-tested-by: syzbot+b3b63b6bff456bd95294@syzkaller.appspotmail.com
Reported-by: syzbot+ba67b12b1ca729912834@syzkaller.appspotmail.com
Cc: Jiri Pirko <jiri@resnulli.us>
Signed-off-by: Cong Wang <cong.wang@bytedance.com>
Tested-by: Jamal Hadi Salim <jhs@mojatatu.com>
Acked-by: Jamal Hadi Salim <jhs@mojatatu.com>
Link: https://lore.kernel.org/r/20210117005657.14810-1-xiyou.wangcong@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
  • Loading branch information
Cong Wang authored and Greg Kroah-Hartman committed Mar 4, 2021
1 parent 750942f commit ad9ed72
Show file tree
Hide file tree
Showing 3 changed files with 79 additions and 41 deletions.
5 changes: 4 additions & 1 deletion include/net/act_api.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -187,10 +187,13 @@ int tcf_action_init(struct net *net, struct tcf_proto *tp, struct nlattr *nla,
struct nlattr *est, char *name, int ovr, int bind,
struct tc_action *actions[], size_t *attr_size,
bool rtnl_held, struct netlink_ext_ack *extack);
struct tc_action_ops *tc_action_load_ops(char *name, struct nlattr *nla,
bool rtnl_held,
struct netlink_ext_ack *extack);
struct tc_action *tcf_action_init_1(struct net *net, struct tcf_proto *tp,
struct nlattr *nla, struct nlattr *est,
char *name, int ovr, int bind,
bool rtnl_held,
struct tc_action_ops *ops, bool rtnl_held,
struct netlink_ext_ack *extack);
int tcf_action_dump(struct sk_buff *skb, struct tc_action *actions[], int bind,
int ref, bool terse);
Expand Down
104 changes: 66 additions & 38 deletions net/sched/act_api.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -928,53 +928,35 @@ void tcf_idr_insert_many(struct tc_action *actions[])
}
}

struct tc_action *tcf_action_init_1(struct net *net, struct tcf_proto *tp,
struct nlattr *nla, struct nlattr *est,
char *name, int ovr, int bind,
bool rtnl_held,
struct netlink_ext_ack *extack)
struct tc_action_ops *tc_action_load_ops(char *name, struct nlattr *nla,
bool rtnl_held,
struct netlink_ext_ack *extack)
{
struct nla_bitfield32 flags = { 0, 0 };
u8 hw_stats = TCA_ACT_HW_STATS_ANY;
struct tc_action *a;
struct nlattr *tb[TCA_ACT_MAX + 1];
struct tc_action_ops *a_o;
struct tc_cookie *cookie = NULL;
char act_name[IFNAMSIZ];
struct nlattr *tb[TCA_ACT_MAX + 1];
struct nlattr *kind;
int err;

if (name == NULL) {
err = nla_parse_nested_deprecated(tb, TCA_ACT_MAX, nla,
tcf_action_policy, extack);
if (err < 0)
goto err_out;
return ERR_PTR(err);
err = -EINVAL;
kind = tb[TCA_ACT_KIND];
if (!kind) {
NL_SET_ERR_MSG(extack, "TC action kind must be specified");
goto err_out;
return ERR_PTR(err);
}
if (nla_strscpy(act_name, kind, IFNAMSIZ) < 0) {
NL_SET_ERR_MSG(extack, "TC action name too long");
goto err_out;
}
if (tb[TCA_ACT_COOKIE]) {
cookie = nla_memdup_cookie(tb);
if (!cookie) {
NL_SET_ERR_MSG(extack, "No memory to generate TC cookie");
err = -ENOMEM;
goto err_out;
}
return ERR_PTR(err);
}
hw_stats = tcf_action_hw_stats_get(tb[TCA_ACT_HW_STATS]);
if (tb[TCA_ACT_FLAGS])
flags = nla_get_bitfield32(tb[TCA_ACT_FLAGS]);
} else {
if (strlcpy(act_name, name, IFNAMSIZ) >= IFNAMSIZ) {
NL_SET_ERR_MSG(extack, "TC action name too long");
err = -EINVAL;
goto err_out;
return ERR_PTR(-EINVAL);
}
}

Expand All @@ -996,24 +978,56 @@ struct tc_action *tcf_action_init_1(struct net *net, struct tcf_proto *tp,
* indicate this using -EAGAIN.
*/
if (a_o != NULL) {
err = -EAGAIN;
goto err_mod;
module_put(a_o->owner);
return ERR_PTR(-EAGAIN);
}
#endif
NL_SET_ERR_MSG(extack, "Failed to load TC action module");
err = -ENOENT;
goto err_free;
return ERR_PTR(-ENOENT);
}

return a_o;
}

struct tc_action *tcf_action_init_1(struct net *net, struct tcf_proto *tp,
struct nlattr *nla, struct nlattr *est,
char *name, int ovr, int bind,
struct tc_action_ops *a_o, bool rtnl_held,
struct netlink_ext_ack *extack)
{
struct nla_bitfield32 flags = { 0, 0 };
u8 hw_stats = TCA_ACT_HW_STATS_ANY;
struct nlattr *tb[TCA_ACT_MAX + 1];
struct tc_cookie *cookie = NULL;
struct tc_action *a;
int err;

/* backward compatibility for policer */
if (name == NULL)
if (name == NULL) {
err = nla_parse_nested_deprecated(tb, TCA_ACT_MAX, nla,
tcf_action_policy, extack);
if (err < 0)
return ERR_PTR(err);
if (tb[TCA_ACT_COOKIE]) {
cookie = nla_memdup_cookie(tb);
if (!cookie) {
NL_SET_ERR_MSG(extack, "No memory to generate TC cookie");
err = -ENOMEM;
goto err_out;
}
}
hw_stats = tcf_action_hw_stats_get(tb[TCA_ACT_HW_STATS]);
if (tb[TCA_ACT_FLAGS])
flags = nla_get_bitfield32(tb[TCA_ACT_FLAGS]);

err = a_o->init(net, tb[TCA_ACT_OPTIONS], est, &a, ovr, bind,
rtnl_held, tp, flags.value, extack);
else
} else {
err = a_o->init(net, nla, est, &a, ovr, bind, rtnl_held,
tp, flags.value, extack);
}
if (err < 0)
goto err_mod;
goto err_out;

if (!name && tb[TCA_ACT_COOKIE])
tcf_set_action_cookie(&a->act_cookie, cookie);
Expand All @@ -1030,14 +1044,11 @@ struct tc_action *tcf_action_init_1(struct net *net, struct tcf_proto *tp,

return a;

err_mod:
module_put(a_o->owner);
err_free:
err_out:
if (cookie) {
kfree(cookie->data);
kfree(cookie);
}
err_out:
return ERR_PTR(err);
}

Expand All @@ -1048,6 +1059,7 @@ int tcf_action_init(struct net *net, struct tcf_proto *tp, struct nlattr *nla,
struct tc_action *actions[], size_t *attr_size,
bool rtnl_held, struct netlink_ext_ack *extack)
{
struct tc_action_ops *ops[TCA_ACT_MAX_PRIO] = {};
struct nlattr *tb[TCA_ACT_MAX_PRIO + 1];
struct tc_action *act;
size_t sz = 0;
Expand All @@ -1059,9 +1071,20 @@ int tcf_action_init(struct net *net, struct tcf_proto *tp, struct nlattr *nla,
if (err < 0)
return err;

for (i = 1; i <= TCA_ACT_MAX_PRIO && tb[i]; i++) {
struct tc_action_ops *a_o;

a_o = tc_action_load_ops(name, tb[i], rtnl_held, extack);
if (IS_ERR(a_o)) {
err = PTR_ERR(a_o);
goto err_mod;
}
ops[i - 1] = a_o;
}

for (i = 1; i <= TCA_ACT_MAX_PRIO && tb[i]; i++) {
act = tcf_action_init_1(net, tp, tb[i], est, name, ovr, bind,
rtnl_held, extack);
ops[i - 1], rtnl_held, extack);
if (IS_ERR(act)) {
err = PTR_ERR(act);
goto err;
Expand All @@ -1081,6 +1104,11 @@ int tcf_action_init(struct net *net, struct tcf_proto *tp, struct nlattr *nla,

err:
tcf_action_destroy(actions, bind);
err_mod:
for (i = 0; i < TCA_ACT_MAX_PRIO; i++) {
if (ops[i])
module_put(ops[i]->owner);
}
return err;
}

Expand Down
11 changes: 9 additions & 2 deletions net/sched/cls_api.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -3043,12 +3043,19 @@ int tcf_exts_validate(struct net *net, struct tcf_proto *tp, struct nlattr **tb,
size_t attr_size = 0;

if (exts->police && tb[exts->police]) {
struct tc_action_ops *a_o;

a_o = tc_action_load_ops("police", tb[exts->police], rtnl_held, extack);
if (IS_ERR(a_o))
return PTR_ERR(a_o);
act = tcf_action_init_1(net, tp, tb[exts->police],
rate_tlv, "police", ovr,
TCA_ACT_BIND, rtnl_held,
TCA_ACT_BIND, a_o, rtnl_held,
extack);
if (IS_ERR(act))
if (IS_ERR(act)) {
module_put(a_o->owner);
return PTR_ERR(act);
}

act->type = exts->type = TCA_OLD_COMPAT;
exts->actions[0] = act;
Expand Down

0 comments on commit ad9ed72

Please sign in to comment.