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Message-ID: <20230418180832.81430-1-kuniyu@amazon.com>
Date: Tue, 18 Apr 2023 11:08:32 -0700
From: Kuniyuki Iwashima <kuniyu@...zon.com>
To: "David S. Miller" <davem@...emloft.net>,
Eric Dumazet <edumazet@...gle.com>,
Jakub Kicinski <kuba@...nel.org>,
Paolo Abeni <pabeni@...hat.com>
CC: Willem de Bruijn <willemb@...gle.com>,
Kuniyuki Iwashima <kuniyu@...zon.com>,
Kuniyuki Iwashima <kuni1840@...il.com>,
<netdev@...r.kernel.org>, syzbot <syzkaller@...glegroups.com>
Subject: [PATCH v2 net] tcp/udp: Fix memleaks of sk and zerocopy skbs with TX timestamp.
syzkaller reported [0] memory leaks of an UDP socket and ZEROCOPY
skbs. We can reproduce the problem with these sequences:
sk = socket(AF_INET, SOCK_DGRAM, 0)
sk.setsockopt(SOL_SOCKET, SO_TIMESTAMPING, SOF_TIMESTAMPING_TX_SOFTWARE)
sk.setsockopt(SOL_SOCKET, SO_ZEROCOPY, 1)
sk.sendto(b'', MSG_ZEROCOPY, ('127.0.0.1', 53))
sk.close()
sendmsg() calls msg_zerocopy_alloc(), which allocates a skb, sets
skb->cb->ubuf.refcnt to 1, and calls sock_hold(). Here, struct
ubuf_info_msgzc indirectly holds a refcnt of the socket. When the
skb is sent, __skb_tstamp_tx() clones it and puts the clone into
the socket's error queue with the TX timestamp.
When the original skb is received locally, skb_copy_ubufs() calls
skb_unclone(), and pskb_expand_head() increments skb->cb->ubuf.refcnt.
This additional count is decremented while freeing the skb, but struct
ubuf_info_msgzc still has a refcnt, so __msg_zerocopy_callback() is
not called.
The last refcnt is not released unless we retrieve the TX timestamped
skb by recvmsg(). When we close() the socket holding such skb, we
never call sock_put() and leak the count, skb, and sk.
To avoid this problem, we must (i) call skb_queue_purge() after
flagging SOCK_DEAD during close() and (ii) make sure that TX tstamp
skb is not queued when SOCK_DEAD is flagged. UDP lacks (i) and (ii),
and TCP lacks (ii).
Without (ii), a skb queued in a qdisc or device could be put into
the error queue after skb_queue_purge().
sendmsg() /* return immediately, but packets
* are queued in a qdisc or device
*/
close()
skb_queue_purge()
__skb_tstamp_tx()
__skb_complete_tx_timestamp()
sock_queue_err_skb()
skb_queue_tail()
Also, we need to check SOCK_DEAD under sk->sk_error_queue.lock
in sock_queue_err_skb() to avoid this race.
if (!sock_flag(sk, SOCK_DEAD))
sock_set_flag(sk, SOCK_DEAD)
skb_queue_purge()
skb_queue_tail()
[0]:
BUG: memory leak
unreferenced object 0xffff88800c6d2d00 (size 1152):
comm "syz-executor392", pid 264, jiffies 4294785440 (age 13.044s)
hex dump (first 32 bytes):
00 00 00 00 00 00 00 00 cd af e8 81 00 00 00 00 ................
02 00 07 40 00 00 00 00 00 00 00 00 00 00 00 00 ...@............
backtrace:
[<0000000055636812>] sk_prot_alloc+0x64/0x2a0 net/core/sock.c:2024
[<0000000054d77b7a>] sk_alloc+0x3b/0x800 net/core/sock.c:2083
[<0000000066f3c7e0>] inet_create net/ipv4/af_inet.c:319 [inline]
[<0000000066f3c7e0>] inet_create+0x31e/0xe40 net/ipv4/af_inet.c:245
[<000000009b83af97>] __sock_create+0x2ab/0x550 net/socket.c:1515
[<00000000b9b11231>] sock_create net/socket.c:1566 [inline]
[<00000000b9b11231>] __sys_socket_create net/socket.c:1603 [inline]
[<00000000b9b11231>] __sys_socket_create net/socket.c:1588 [inline]
[<00000000b9b11231>] __sys_socket+0x138/0x250 net/socket.c:1636
[<000000004fb45142>] __do_sys_socket net/socket.c:1649 [inline]
[<000000004fb45142>] __se_sys_socket net/socket.c:1647 [inline]
[<000000004fb45142>] __x64_sys_socket+0x73/0xb0 net/socket.c:1647
[<0000000066999e0e>] do_syscall_x64 arch/x86/entry/common.c:50 [inline]
[<0000000066999e0e>] do_syscall_64+0x38/0x90 arch/x86/entry/common.c:80
[<0000000017f238c1>] entry_SYSCALL_64_after_hwframe+0x63/0xcd
BUG: memory leak
unreferenced object 0xffff888017633a00 (size 240):
comm "syz-executor392", pid 264, jiffies 4294785440 (age 13.044s)
hex dump (first 32 bytes):
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00 00 00 00 00 00 00 00 00 2d 6d 0c 80 88 ff ff .........-m.....
backtrace:
[<000000002b1c4368>] __alloc_skb+0x229/0x320 net/core/skbuff.c:497
[<00000000143579a6>] alloc_skb include/linux/skbuff.h:1265 [inline]
[<00000000143579a6>] sock_omalloc+0xaa/0x190 net/core/sock.c:2596
[<00000000be626478>] msg_zerocopy_alloc net/core/skbuff.c:1294 [inline]
[<00000000be626478>] msg_zerocopy_realloc+0x1ce/0x7f0 net/core/skbuff.c:1370
[<00000000cbfc9870>] __ip_append_data+0x2adf/0x3b30 net/ipv4/ip_output.c:1037
[<0000000089869146>] ip_make_skb+0x26c/0x2e0 net/ipv4/ip_output.c:1652
[<00000000098015c2>] udp_sendmsg+0x1bac/0x2390 net/ipv4/udp.c:1253
[<0000000045e0e95e>] inet_sendmsg+0x10a/0x150 net/ipv4/af_inet.c:819
[<000000008d31bfde>] sock_sendmsg_nosec net/socket.c:714 [inline]
[<000000008d31bfde>] sock_sendmsg+0x141/0x190 net/socket.c:734
[<0000000021e21aa4>] __sys_sendto+0x243/0x360 net/socket.c:2117
[<00000000ac0af00c>] __do_sys_sendto net/socket.c:2129 [inline]
[<00000000ac0af00c>] __se_sys_sendto net/socket.c:2125 [inline]
[<00000000ac0af00c>] __x64_sys_sendto+0xe1/0x1c0 net/socket.c:2125
[<0000000066999e0e>] do_syscall_x64 arch/x86/entry/common.c:50 [inline]
[<0000000066999e0e>] do_syscall_64+0x38/0x90 arch/x86/entry/common.c:80
[<0000000017f238c1>] entry_SYSCALL_64_after_hwframe+0x63/0xcd
Fixes: f214f915e7db ("tcp: enable MSG_ZEROCOPY")
Fixes: b5947e5d1e71 ("udp: msg_zerocopy")
Reported-by: syzbot <syzkaller@...glegroups.com>
Signed-off-by: Kuniyuki Iwashima <kuniyu@...zon.com>
---
v2:
* Move skb_queue_purge() after setting SOCK_DEAD in udp_destroy_sock()
* Check SOCK_DEAD in sock_queue_err_skb() with sk_error_queue.lock
* Add Fixes tag for TCP
v1: https://lore.kernel.org/netdev/20230417171155.22916-1-kuniyu@amazon.com/
---
net/core/skbuff.c | 15 ++++++++++++---
net/ipv4/udp.c | 5 +++++
2 files changed, 17 insertions(+), 3 deletions(-)
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 4c0879798eb8..287b834df9c8 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -4979,6 +4979,8 @@ static void skb_set_err_queue(struct sk_buff *skb)
*/
int sock_queue_err_skb(struct sock *sk, struct sk_buff *skb)
{
+ unsigned long flags;
+
if (atomic_read(&sk->sk_rmem_alloc) + skb->truesize >=
(unsigned int)READ_ONCE(sk->sk_rcvbuf))
return -ENOMEM;
@@ -4992,9 +4994,16 @@ int sock_queue_err_skb(struct sock *sk, struct sk_buff *skb)
/* before exiting rcu section, make sure dst is refcounted */
skb_dst_force(skb);
- skb_queue_tail(&sk->sk_error_queue, skb);
- if (!sock_flag(sk, SOCK_DEAD))
- sk_error_report(sk);
+ spin_lock_irqsave(&sk->sk_error_queue.lock, flags);
+ if (sock_flag(sk, SOCK_DEAD)) {
+ spin_unlock_irqrestore(&sk->sk_error_queue.lock, flags);
+ return -EINVAL;
+ }
+ __skb_queue_tail(&sk->sk_error_queue, skb);
+ spin_unlock_irqrestore(&sk->sk_error_queue.lock, flags);
+
+ sk_error_report(sk);
+
return 0;
}
EXPORT_SYMBOL(sock_queue_err_skb);
diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index c605d171eb2d..7060a5cda711 100644
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -2674,6 +2674,11 @@ void udp_destroy_sock(struct sock *sk)
if (up->encap_enabled)
static_branch_dec(&udp_encap_needed_key);
}
+
+ /* A zerocopy skb has a refcnt of sk and may be
+ * put into sk_error_queue with TX timestamp
+ */
+ skb_queue_purge(&sk->sk_error_queue);
}
/*
--
2.30.2
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