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Message-ID: <644702c8e1ec5_1ad44a29462@willemb.c.googlers.com.notmuch> Date: Mon, 24 Apr 2023 18:29:28 -0400 From: Willem de Bruijn <willemdebruijn.kernel@...il.com> To: Kuniyuki Iwashima <kuniyu@...zon.com>, "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: RE: [PATCH v4 net] tcp/udp: Fix memleaks of sk and zerocopy skbs with TX timestamp. Kuniyuki Iwashima wrote: > 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@...glegroups.com> > Signed-off-by: Kuniyuki Iwashima <kuniyu@...zon.com> Reviewed-by: Willem de Bruijn <willemb@...gle.com> Thanks for the analysis and fix!
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