From: Kuniyuki Iwashima kuniyu@amazon.com
[ Upstream commit 50749f2dd6854a41830996ad302aef2ffaf011d8 ]
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(). Since we clear the error queue in inet_sock_destruct() after the socket's refcnt reaches 0, there is a circular dependency. If we close() the socket holding such skbs, we never call sock_put() and leak the count, sk, and skb.
TCP has the same problem, and commit e0c8bccd40fc ("net: stream: purge sk_error_queue in sk_stream_kill_queues()") tried to fix it by calling skb_queue_purge() during close(). However, there is a small chance that skb queued in a qdisc or device could be put into the error queue after the skb_queue_purge() call.
In __skb_tstamp_tx(), the cloned skb should not have a reference to the ubuf to remove the circular dependency, but skb_clone() does not call skb_copy_ubufs() for zerocopy skb. So, we need to call skb_orphan_frags_rx() for the cloned skb to call skb_copy_ubufs().
[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@googlegroups.com Signed-off-by: Kuniyuki Iwashima kuniyu@amazon.com Reviewed-by: Willem de Bruijn willemb@google.com Signed-off-by: David S. Miller davem@davemloft.net Signed-off-by: Sasha Levin sashal@kernel.org --- net/core/skbuff.c | 3 +++ 1 file changed, 3 insertions(+)
diff --git a/net/core/skbuff.c b/net/core/skbuff.c index 46cc3a7632f79..d4b25d6fd01d5 100644 --- a/net/core/skbuff.c +++ b/net/core/skbuff.c @@ -4960,6 +4960,9 @@ void __skb_tstamp_tx(struct sk_buff *orig_skb, skb = alloc_skb(0, GFP_ATOMIC); } else { skb = skb_clone(orig_skb, GFP_ATOMIC); + + if (skb_orphan_frags_rx(skb, GFP_ATOMIC)) + return; } if (!skb) return;