netdev - [PATCH net] net: Fix memory leaks of napi->rx

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Date:   Wed, 2 Nov 2022 11:54:34 +0800
From:   Wang Yufen <wangyufen@...wei.com>
To:     <netdev@...r.kernel.org>, <bpf@...r.kernel.org>
CC:     <davem@...emloft.net>, <edumazet@...gle.com>, <kuba@...nel.org>,
        <pabeni@...hat.com>, <ecree@...arflare.com>,
        Wang Yufen <wangyufen@...wei.com>
Subject: [PATCH net] net: Fix memory leaks of napi->rx_list

kmemleak reports after running test_progs:

unreferenced object 0xffff8881b1672dc0 (size 232):
  comm "test_progs", pid 394388, jiffies 4354712116 (age 841.975s)
  hex dump (first 32 bytes):
    e0 84 d7 a8 81 88 ff ff 80 2c 67 b1 81 88 ff ff  .........,g.....
    00 40 c5 9b 81 88 ff ff 00 00 00 00 00 00 00 00  .@..............
  backtrace:
    [<00000000c8f01748>] napi_skb_cache_get+0xd4/0x150
    [<0000000041c7fc09>] __napi_build_skb+0x15/0x50
    [<00000000431c7079>] __napi_alloc_skb+0x26e/0x540
    [<000000003ecfa30e>] napi_get_frags+0x59/0x140
    [<0000000099b2199e>] tun_get_user+0x183d/0x3bb0 [tun]
    [<000000008a5adef0>] tun_chr_write_iter+0xc0/0x1b1 [tun]
    [<0000000049993ff4>] do_iter_readv_writev+0x19f/0x320
    [<000000008f338ea2>] do_iter_write+0x135/0x630
    [<000000008a3377a4>] vfs_writev+0x12e/0x440
    [<00000000a6b5639a>] do_writev+0x104/0x280
    [<00000000ccf065d8>] do_syscall_64+0x3b/0x90
    [<00000000d776e329>] entry_SYSCALL_64_after_hwframe+0x63/0xcd

The issue occurs in the following scenarios:
tun_get_user()
  napi_gro_frags()
    napi_frags_finish()
      case GRO_NORMAL:
        gro_normal_one()
          list_add_tail(&skb->list, &napi->rx_list);
          <-- While napi->rx_count < READ_ONCE(gro_normal_batch),
          <-- gro_normal_list() is not called, napi->rx_list is not empty
...
netif_napi_del()
  __netif_napi_del()
  <-- &napi->rx_list is not empty, which caused memory leaks

To fix, add flush_rx_list() to free skbs in napi->rx_list.

Fixes: 323ebb61e32b ("net: use listified RX for handling GRO_NORMAL skbs")
Signed-off-by: Wang Yufen <wangyufen@...wei.com>
---
 net/core/dev.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/net/core/dev.c b/net/core/dev.c
index 3be2560..de3bc9c 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -6461,6 +6461,16 @@ static void flush_gro_hash(struct napi_struct *napi)
 	}
 }
 
+static void flush_rx_list(struct napi_struct *napi)
+{
+	struct sk_buff *skb, *next;
+
+	list_for_each_entry_safe(skb, next, &napi->rx_list, list) {
+		skb_list_del_init(skb);
+		kfree_skb(skb);
+	}
+}
+
 /* Must be called in process context */
 void __netif_napi_del(struct napi_struct *napi)
 {
@@ -6471,6 +6481,7 @@ void __netif_napi_del(struct napi_struct *napi)
 	list_del_rcu(&napi->dev_list);
 	napi_free_frags(napi);
 
+	flush_rx_list(napi);
 	flush_gro_hash(napi);
 	napi->gro_bitmask = 0;
 
-- 
1.8.3.1