| Message ID | 20241009174226.7738-1-kuniyu@amazon.com (mailing list archive) |
|---|---|
| State | Superseded |
| Delegated to: | Netdev Maintainers |
| Headers | show |
| Series | [v2,net] tcp/dccp: Don't use timer_pending() in reqsk_queue_unlink(). | expand |
On 10/9/24 10:42 AM, Kuniyuki Iwashima wrote: > diff --git a/net/ipv4/inet_connection_sock.c b/net/ipv4/inet_connection_sock.c > index 2c5632d4fddb..23cff5278a64 100644 > --- a/net/ipv4/inet_connection_sock.c > +++ b/net/ipv4/inet_connection_sock.c > @@ -1045,12 +1045,13 @@ static bool reqsk_queue_unlink(struct request_sock *req) > found = __sk_nulls_del_node_init_rcu(sk); > spin_unlock(lock); > } > - if (timer_pending(&req->rsk_timer) && del_timer_sync(&req->rsk_timer)) > - reqsk_put(req); > + > return found; > } > > -bool inet_csk_reqsk_queue_drop(struct sock *sk, struct request_sock *req) > +static bool __inet_csk_reqsk_queue_drop(struct sock *sk, > + struct request_sock *req, > + bool from_timer) > { > bool unlinked = reqsk_queue_unlink(req); > > @@ -1058,8 +1059,17 @@ bool inet_csk_reqsk_queue_drop(struct sock *sk, struct request_sock *req) > reqsk_queue_removed(&inet_csk(sk)->icsk_accept_queue, req); > reqsk_put(req); > } > + > + if (!from_timer && timer_delete_sync(&req->rsk_timer)) timer_delete_sync() is now done after the above reqsk_queue_removed(). The reqsk_timer_handler() may do the "req->num_timeout++" while the above reqsk_queue_removed() needs to check for req->num_timeout. Would it race? Others lgtm. Thanks for the patch. > + reqsk_put(req); > + > return unlinked; > }
From: Martin KaFai Lau <martin.lau@linux.dev> Date: Wed, 9 Oct 2024 22:46:57 -0700 > On 10/9/24 10:42 AM, Kuniyuki Iwashima wrote: > > diff --git a/net/ipv4/inet_connection_sock.c b/net/ipv4/inet_connection_sock.c > > index 2c5632d4fddb..23cff5278a64 100644 > > --- a/net/ipv4/inet_connection_sock.c > > +++ b/net/ipv4/inet_connection_sock.c > > @@ -1045,12 +1045,13 @@ static bool reqsk_queue_unlink(struct request_sock *req) > > found = __sk_nulls_del_node_init_rcu(sk); > > spin_unlock(lock); > > } > > - if (timer_pending(&req->rsk_timer) && del_timer_sync(&req->rsk_timer)) > > - reqsk_put(req); > > + > > return found; > > } > > > > -bool inet_csk_reqsk_queue_drop(struct sock *sk, struct request_sock *req) > > +static bool __inet_csk_reqsk_queue_drop(struct sock *sk, > > + struct request_sock *req, > > + bool from_timer) > > { > > bool unlinked = reqsk_queue_unlink(req); > > > > @@ -1058,8 +1059,17 @@ bool inet_csk_reqsk_queue_drop(struct sock *sk, struct request_sock *req) > > reqsk_queue_removed(&inet_csk(sk)->icsk_accept_queue, req); > > reqsk_put(req); > > } > > + > > + if (!from_timer && timer_delete_sync(&req->rsk_timer)) > > timer_delete_sync() is now done after the above reqsk_queue_removed(). > The reqsk_timer_handler() may do the "req->num_timeout++" while the above > reqsk_queue_removed() needs to check for req->num_timeout. Would it race? Ah thanks! I moved it for better @unlinked access, but will move above. Btw, do you have any hint why the connection was processed on a different cpu, not one where reqsk timer was pinned ?
On 10/10/24 10:36 AM, Kuniyuki Iwashima wrote: > From: Martin KaFai Lau <martin.lau@linux.dev> > Date: Wed, 9 Oct 2024 22:46:57 -0700 >> On 10/9/24 10:42 AM, Kuniyuki Iwashima wrote: >>> diff --git a/net/ipv4/inet_connection_sock.c b/net/ipv4/inet_connection_sock.c >>> index 2c5632d4fddb..23cff5278a64 100644 >>> --- a/net/ipv4/inet_connection_sock.c >>> +++ b/net/ipv4/inet_connection_sock.c >>> @@ -1045,12 +1045,13 @@ static bool reqsk_queue_unlink(struct request_sock *req) >>> found = __sk_nulls_del_node_init_rcu(sk); >>> spin_unlock(lock); >>> } >>> - if (timer_pending(&req->rsk_timer) && del_timer_sync(&req->rsk_timer)) >>> - reqsk_put(req); >>> + >>> return found; >>> } >>> >>> -bool inet_csk_reqsk_queue_drop(struct sock *sk, struct request_sock *req) >>> +static bool __inet_csk_reqsk_queue_drop(struct sock *sk, >>> + struct request_sock *req, >>> + bool from_timer) >>> { >>> bool unlinked = reqsk_queue_unlink(req); >>> >>> @@ -1058,8 +1059,17 @@ bool inet_csk_reqsk_queue_drop(struct sock *sk, struct request_sock *req) >>> reqsk_queue_removed(&inet_csk(sk)->icsk_accept_queue, req); >>> reqsk_put(req); >>> } >>> + >>> + if (!from_timer && timer_delete_sync(&req->rsk_timer)) >> >> timer_delete_sync() is now done after the above reqsk_queue_removed(). >> The reqsk_timer_handler() may do the "req->num_timeout++" while the above >> reqsk_queue_removed() needs to check for req->num_timeout. Would it race? > > Ah thanks! > I moved it for better @unlinked access, but will move above. > > Btw, do you have any hint why the connection was processed on a different > cpu, not one where reqsk timer was pinned ? Just saw this after replying on v1. I don't know what exactly caused this. I am only aware we have a recent steering test to test different packet steering setup. [ I had some email client issues, so the reply ordering has been wrong :( ]
diff --git a/net/ipv4/inet_connection_sock.c b/net/ipv4/inet_connection_sock.c index 2c5632d4fddb..23cff5278a64 100644 --- a/net/ipv4/inet_connection_sock.c +++ b/net/ipv4/inet_connection_sock.c @@ -1045,12 +1045,13 @@ static bool reqsk_queue_unlink(struct request_sock *req) found = __sk_nulls_del_node_init_rcu(sk); spin_unlock(lock); } - if (timer_pending(&req->rsk_timer) && del_timer_sync(&req->rsk_timer)) - reqsk_put(req); + return found; } -bool inet_csk_reqsk_queue_drop(struct sock *sk, struct request_sock *req) +static bool __inet_csk_reqsk_queue_drop(struct sock *sk, + struct request_sock *req, + bool from_timer) { bool unlinked = reqsk_queue_unlink(req); @@ -1058,8 +1059,17 @@ bool inet_csk_reqsk_queue_drop(struct sock *sk, struct request_sock *req) reqsk_queue_removed(&inet_csk(sk)->icsk_accept_queue, req); reqsk_put(req); } + + if (!from_timer && timer_delete_sync(&req->rsk_timer)) + reqsk_put(req); + return unlinked; } + +bool inet_csk_reqsk_queue_drop(struct sock *sk, struct request_sock *req) +{ + return __inet_csk_reqsk_queue_drop(sk, req, false); +} EXPORT_SYMBOL(inet_csk_reqsk_queue_drop); void inet_csk_reqsk_queue_drop_and_put(struct sock *sk, struct request_sock *req) @@ -1152,7 +1162,7 @@ static void reqsk_timer_handler(struct timer_list *t) if (!inet_ehash_insert(req_to_sk(nreq), req_to_sk(oreq), NULL)) { /* delete timer */ - inet_csk_reqsk_queue_drop(sk_listener, nreq); + __inet_csk_reqsk_queue_drop(sk_listener, nreq, true); goto no_ownership; } @@ -1178,7 +1188,8 @@ static void reqsk_timer_handler(struct timer_list *t) } drop: - inet_csk_reqsk_queue_drop_and_put(oreq->rsk_listener, oreq); + __inet_csk_reqsk_queue_drop(sk_listener, oreq, true); + reqsk_put(req); } static bool reqsk_queue_hash_req(struct request_sock *req,
Martin KaFai Lau reported use-after-free [0] in reqsk_timer_handler(). """ We are seeing a use-after-free from a bpf prog attached to trace_tcp_retransmit_synack. The program passes the req->sk to the bpf_sk_storage_get_tracing kernel helper which does check for null before using it. """ The commit 83fccfc3940c ("inet: fix potential deadlock in reqsk_queue_unlink()") added timer_pending() in reqsk_queue_unlink() not to call del_timer_sync() from reqsk_timer_handler(), but it introduced a small race window. Before the timer is called, expire_timers() calls detach_timer(timer, true) to clear timer->entry.pprev and marks it as not pending. If reqsk_queue_unlink() checks timer_pending() just before expire_timers() calls detach_timer(), TCP will miss del_timer_sync(); the reqsk timer will continue running and send multiple SYN+ACKs until it expires. The reported UAF could happen if req->sk is close()d earlier than the timer expiration, which is 63s by default. The scenario would be 1. inet_csk_complete_hashdance() calls inet_csk_reqsk_queue_drop(), but del_timer_sync() is missed 2. reqsk timer is executed and scheduled again 3. req->sk is accept()ed and reqsk_put() decrements rsk_refcnt, but reqsk timer still has another one, and inet_csk_accept() does not clear req->sk for non-TFO sockets 4. sk is close()d 5. reqsk timer is executed again, and BPF touches req->sk Let's not use timer_pending() by passing the caller context to __inet_csk_reqsk_queue_drop(). Note that reqsk timer is pinned, so del_timer_sync() should not be missed in most use cases. [0] BUG: KFENCE: use-after-free read in bpf_sk_storage_get_tracing+0x2e/0x1b0 Use-after-free read at 0x00000000a891fb3a (in kfence-#1): bpf_sk_storage_get_tracing+0x2e/0x1b0 bpf_prog_5ea3e95db6da0438_tcp_retransmit_synack+0x1d20/0x1dda bpf_trace_run2+0x4c/0xc0 tcp_rtx_synack+0xf9/0x100 reqsk_timer_handler+0xda/0x3d0 run_timer_softirq+0x292/0x8a0 irq_exit_rcu+0xf5/0x320 sysvec_apic_timer_interrupt+0x6d/0x80 asm_sysvec_apic_timer_interrupt+0x16/0x20 intel_idle_irq+0x5a/0xa0 cpuidle_enter_state+0x94/0x273 cpu_startup_entry+0x15e/0x260 start_secondary+0x8a/0x90 secondary_startup_64_no_verify+0xfa/0xfb kfence-#1: 0x00000000a72cc7b6-0x00000000d97616d9, size=2376, cache=TCPv6 allocated by task 0 on cpu 9 at 260507.901592s: sk_prot_alloc+0x35/0x140 sk_clone_lock+0x1f/0x3f0 inet_csk_clone_lock+0x15/0x160 tcp_create_openreq_child+0x1f/0x410 tcp_v6_syn_recv_sock+0x1da/0x700 tcp_check_req+0x1fb/0x510 tcp_v6_rcv+0x98b/0x1420 ipv6_list_rcv+0x2258/0x26e0 napi_complete_done+0x5b1/0x2990 mlx5e_napi_poll+0x2ae/0x8d0 net_rx_action+0x13e/0x590 irq_exit_rcu+0xf5/0x320 common_interrupt+0x80/0x90 asm_common_interrupt+0x22/0x40 cpuidle_enter_state+0xfb/0x273 cpu_startup_entry+0x15e/0x260 start_secondary+0x8a/0x90 secondary_startup_64_no_verify+0xfa/0xfb freed by task 0 on cpu 9 at 260507.927527s: rcu_core_si+0x4ff/0xf10 irq_exit_rcu+0xf5/0x320 sysvec_apic_timer_interrupt+0x6d/0x80 asm_sysvec_apic_timer_interrupt+0x16/0x20 cpuidle_enter_state+0xfb/0x273 cpu_startup_entry+0x15e/0x260 start_secondary+0x8a/0x90 secondary_startup_64_no_verify+0xfa/0xfb Fixes: 83fccfc3940c ("inet: fix potential deadlock in reqsk_queue_unlink()") Reported-by: Martin KaFai Lau <martin.lau@kernel.org> Closes: https://lore.kernel.org/netdev/eb6684d0-ffd9-4bdc-9196-33f690c25824@linux.dev/ Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com> --- v2: * Added issue scenario in changelog * Correct reqsk for __inet_csk_reqsk_queue_drop() v1: https://lore.kernel.org/netdev/20241007141557.14424-1-kuniyu@amazon.com/ --- net/ipv4/inet_connection_sock.c | 21 ++++++++++++++++----- 1 file changed, 16 insertions(+), 5 deletions(-)