[PATCH net 0/2] net/sched: two fixes for cls_u32

[PATCH net 0/2] net/sched: two fixes for cls_u32

[Eric Dumazet]

From: Eric Dumazet <edumazet@google.com>

One syzbot report brought my attention to cls_u32.

This series addresses the syzbot report, and an additional
issue discovered in code review.

Eric Dumazet (2):
  net/sched: cls_u32: fix netns refcount changes in u32_change()
  net/sched: cls_u32: fix possible leak in u32_init_knode()

 net/sched/cls_u32.c | 24 ++++++++++++++----------
 1 file changed, 14 insertions(+), 10 deletions(-)

-- 
2.35.1.1178.g4f1659d476-goog

[PATCH net 1/2] net/sched: cls_u32: fix netns refcount changes in u32_change()

[Eric Dumazet]

From: Eric Dumazet <edumazet@google.com>

We are now able to detect extra put_net() at the moment
they happen, instead of much later in correct code paths.

u32_init_knode() / tcf_exts_init() populates the ->exts.net
pointer, but as mentioned in tcf_exts_init(),
the refcount on netns has not been elevated yet.

The refcount is taken only once tcf_exts_get_net()
is called.

So the two u32_destroy_key() calls from u32_change()
are attempting to release an invalid reference on the netns.

syzbot report:

refcount_t: decrement hit 0; leaking memory.
WARNING: CPU: 0 PID: 21708 at lib/refcount.c:31 refcount_warn_saturate+0xbf/0x1e0 lib/refcount.c:31
Modules linked in:
CPU: 0 PID: 21708 Comm: syz-executor.5 Not tainted 5.18.0-rc2-next-20220412-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
RIP: 0010:refcount_warn_saturate+0xbf/0x1e0 lib/refcount.c:31
Code: 1d 14 b6 b2 09 31 ff 89 de e8 6d e9 89 fd 84 db 75 e0 e8 84 e5 89 fd 48 c7 c7 40 aa 26 8a c6 05 f4 b5 b2 09 01 e8 e5 81 2e 05 <0f> 0b eb c4 e8 68 e5 89 fd 0f b6 1d e3 b5 b2 09 31 ff 89 de e8 38
RSP: 0018:ffffc900051af1b0 EFLAGS: 00010286
RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000
RDX: 0000000000040000 RSI: ffffffff8160a0c8 RDI: fffff52000a35e28
RBP: 0000000000000004 R08: 0000000000000000 R09: 0000000000000000
R10: ffffffff81604a9e R11: 0000000000000000 R12: 1ffff92000a35e3b
R13: 00000000ffffffef R14: ffff8880211a0194 R15: ffff8880577d0a00
FS:  00007f25d183e700(0000) GS:ffff8880b9c00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f19c859c028 CR3: 0000000051009000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 __refcount_dec include/linux/refcount.h:344 [inline]
 refcount_dec include/linux/refcount.h:359 [inline]
 ref_tracker_free+0x535/0x6b0 lib/ref_tracker.c:118
 netns_tracker_free include/net/net_namespace.h:327 [inline]
 put_net_track include/net/net_namespace.h:341 [inline]
 tcf_exts_put_net include/net/pkt_cls.h:255 [inline]
 u32_destroy_key.isra.0+0xa7/0x2b0 net/sched/cls_u32.c:394
 u32_change+0xe01/0x3140 net/sched/cls_u32.c:909
 tc_new_tfilter+0x98d/0x2200 net/sched/cls_api.c:2148
 rtnetlink_rcv_msg+0x80d/0xb80 net/core/rtnetlink.c:6016
 netlink_rcv_skb+0x153/0x420 net/netlink/af_netlink.c:2495
 netlink_unicast_kernel net/netlink/af_netlink.c:1319 [inline]
 netlink_unicast+0x543/0x7f0 net/netlink/af_netlink.c:1345
 netlink_sendmsg+0x904/0xe00 net/netlink/af_netlink.c:1921
 sock_sendmsg_nosec net/socket.c:705 [inline]
 sock_sendmsg+0xcf/0x120 net/socket.c:725
 ____sys_sendmsg+0x6e2/0x800 net/socket.c:2413
 ___sys_sendmsg+0xf3/0x170 net/socket.c:2467
 __sys_sendmsg+0xe5/0x1b0 net/socket.c:2496
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae
RIP: 0033:0x7f25d0689049
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 b8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f25d183e168 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00007f25d079c030 RCX: 00007f25d0689049
RDX: 0000000000000000 RSI: 0000000020000340 RDI: 0000000000000005
RBP: 00007f25d06e308d R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007ffd0b752e3f R14: 00007f25d183e300 R15: 0000000000022000
 </TASK>

Fixes: 35c55fc156d8 ("cls_u32: use tcf_exts_get_net() before call_rcu()")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: syzbot <syzkaller@googlegroups.com>
Cc: Jamal Hadi Salim <jhs@mojatatu.com>
Cc: Cong Wang <xiyou.wangcong@gmail.com>
Cc: Jiri Pirko <jiri@resnulli.us>
---
 net/sched/cls_u32.c | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/net/sched/cls_u32.c b/net/sched/cls_u32.c
index cf5649292ee00941e5c4a4d5b11b1c3dc98cce3f..fcba6c43ba509a069c593d525daf2943b4079538 100644
--- a/net/sched/cls_u32.c
+++ b/net/sched/cls_u32.c
@@ -386,14 +386,19 @@ static int u32_init(struct tcf_proto *tp)
 	return 0;
 }
 
-static int u32_destroy_key(struct tc_u_knode *n, bool free_pf)
+static void __u32_destroy_key(struct tc_u_knode *n)
 {
 	struct tc_u_hnode *ht = rtnl_dereference(n->ht_down);
 
 	tcf_exts_destroy(&n->exts);
-	tcf_exts_put_net(&n->exts);
 	if (ht && --ht->refcnt == 0)
 		kfree(ht);
+	kfree(n);
+}
+
+static void u32_destroy_key(struct tc_u_knode *n, bool free_pf)
+{
+	tcf_exts_put_net(&n->exts);
 #ifdef CONFIG_CLS_U32_PERF
 	if (free_pf)
 		free_percpu(n->pf);
@@ -402,8 +407,7 @@ static int u32_destroy_key(struct tc_u_knode *n, bool free_pf)
 	if (free_pf)
 		free_percpu(n->pcpu_success);
 #endif
-	kfree(n);
-	return 0;
+	__u32_destroy_key(n);
 }
 
 /* u32_delete_key_rcu should be called when free'ing a copied
@@ -900,13 +904,13 @@ static int u32_change(struct net *net, struct sk_buff *in_skb,
 				    extack);
 
 		if (err) {
-			u32_destroy_key(new, false);
+			__u32_destroy_key(new);
 			return err;
 		}
 
 		err = u32_replace_hw_knode(tp, new, flags, extack);
 		if (err) {
-			u32_destroy_key(new, false);
+			__u32_destroy_key(new);
 			return err;
 		}
 
-- 
2.35.1.1178.g4f1659d476-goog

Re: [PATCH net 1/2] net/sched: cls_u32: fix netns refcount changes in u32_change()

[Jamal Hadi Salim]

On 2022-04-13 13:35, Eric Dumazet wrote:
> From: Eric Dumazet <edumazet@google.com>
> 
> We are now able to detect extra put_net() at the moment
> they happen, instead of much later in correct code paths.
> 
> u32_init_knode() / tcf_exts_init() populates the ->exts.net
> pointer, but as mentioned in tcf_exts_init(),
> the refcount on netns has not been elevated yet.
> 
> The refcount is taken only once tcf_exts_get_net()
> is called.
> 
> So the two u32_destroy_key() calls from u32_change()
> are attempting to release an invalid reference on the netns.
> 

Looks good to me.

Acked-by: Jamal Hadi Salim <jhs@mojatatu.com>

cheers,
jamal

[PATCH net 2/2] net/sched: cls_u32: fix possible leak in u32_init_knode()

[Eric Dumazet]

From: Eric Dumazet <edumazet@google.com>

While investigating a related syzbot report,
I found that whenever call to tcf_exts_init()
from u32_init_knode() is failing, we end up
with an elevated refcount on ht->refcnt

To avoid that, only increase the refcount after
all possible errors have been evaluated.

Fixes: b9a24bb76bf6 ("net_sched: properly handle failure case of tcf_exts_init()")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Jamal Hadi Salim <jhs@mojatatu.com>
Cc: Cong Wang <xiyou.wangcong@gmail.com>
Cc: Jiri Pirko <jiri@resnulli.us>
---
 net/sched/cls_u32.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/net/sched/cls_u32.c b/net/sched/cls_u32.c
index fcba6c43ba509a069c593d525daf2943b4079538..4d27300c287c46d11bf9d44f8c66eded9e734581 100644
--- a/net/sched/cls_u32.c
+++ b/net/sched/cls_u32.c
@@ -815,10 +815,6 @@ static struct tc_u_knode *u32_init_knode(struct net *net, struct tcf_proto *tp,
 	new->flags = n->flags;
 	RCU_INIT_POINTER(new->ht_down, ht);
 
-	/* bump reference count as long as we hold pointer to structure */
-	if (ht)
-		ht->refcnt++;
-
 #ifdef CONFIG_CLS_U32_PERF
 	/* Statistics may be incremented by readers during update
 	 * so we must keep them in tact. When the node is later destroyed
@@ -840,6 +836,10 @@ static struct tc_u_knode *u32_init_knode(struct net *net, struct tcf_proto *tp,
 		return NULL;
 	}
 
+	/* bump reference count as long as we hold pointer to structure */
+	if (ht)
+		ht->refcnt++;
+
 	return new;
 }
 
-- 
2.35.1.1178.g4f1659d476-goog

Re: [PATCH net 2/2] net/sched: cls_u32: fix possible leak in u32_init_knode()

[Jamal Hadi Salim]

On 2022-04-13 13:35, Eric Dumazet wrote:
> From: Eric Dumazet<edumazet@google.com>
> 
> While investigating a related syzbot report,
> I found that whenever call to tcf_exts_init()
> from u32_init_knode() is failing, we end up
> with an elevated refcount on ht->refcnt
> 
> To avoid that, only increase the refcount after
> all possible errors have been evaluated.
> 
> Fixes: b9a24bb76bf6 ("net_sched: properly handle failure case of tcf_exts_init()")
> Signed-off-by: Eric Dumazet<edumazet@google.com>
> Cc: Jamal Hadi Salim<jhs@mojatatu.com>
> Cc: Cong Wang<xiyou.wangcong@gmail.com>
> Cc: Jiri Pirko<jiri@resnulli.us>


Acked-by: Jamal Hadi Salim <jhs@mojatatu.com>


cheers,
jamal

Re: [PATCH net 0/2] net/sched: two fixes for cls_u32

[patchwork-bot+netdevbpf]

Hello:

This series was applied to netdev/net.git (master)
by Jakub Kicinski <kuba@kernel.org>:

On Wed, 13 Apr 2022 10:35:40 -0700 you wrote:
> From: Eric Dumazet <edumazet@google.com>
> 
> One syzbot report brought my attention to cls_u32.
> 
> This series addresses the syzbot report, and an additional
> issue discovered in code review.
> 
> [...]

Here is the summary with links:
  - [net,1/2] net/sched: cls_u32: fix netns refcount changes in u32_change()
    https://git.kernel.org/netdev/net/c/3db09e762dc7
  - [net,2/2] net/sched: cls_u32: fix possible leak in u32_init_knode()
    https://git.kernel.org/netdev/net/c/ec5b0f605b10

You are awesome, thank you!
-- 
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