From 93dd5f185916b05e931cffae636596f21f98546e Mon Sep 17 00:00:00 2001 From: John Fastabend Date: Thu, 25 Jun 2020 16:12:59 -0700 Subject: bpf, sockmap: RCU splat with redirect and strparser error or TLS There are two paths to generate the below RCU splat the first and most obvious is the result of the BPF verdict program issuing a redirect on a TLS socket (This is the splat shown below). Unlike the non-TLS case the caller of the *strp_read() hooks does not wrap the call in a rcu_read_lock/unlock. Then if the BPF program issues a redirect action we hit the RCU splat. However, in the non-TLS socket case the splat appears to be relatively rare, because the skmsg caller into the strp_data_ready() is wrapped in a rcu_read_lock/unlock. Shown here, static void sk_psock_strp_data_ready(struct sock *sk) { struct sk_psock *psock; rcu_read_lock(); psock = sk_psock(sk); if (likely(psock)) { if (tls_sw_has_ctx_rx(sk)) { psock->parser.saved_data_ready(sk); } else { write_lock_bh(&sk->sk_callback_lock); strp_data_ready(&psock->parser.strp); write_unlock_bh(&sk->sk_callback_lock); } } rcu_read_unlock(); } If the above was the only way to run the verdict program we would be safe. But, there is a case where the strparser may throw an ENOMEM error while parsing the skb. This is a result of a failed skb_clone, or alloc_skb_for_msg while building a new merged skb when the msg length needed spans multiple skbs. This will in turn put the skb on the strp_wrk workqueue in the strparser code. The skb will later be dequeued and verdict programs run, but now from a different context without the rcu_read_lock()/unlock() critical section in sk_psock_strp_data_ready() shown above. In practice I have not seen this yet, because as far as I know most users of the verdict programs are also only working on single skbs. In this case no merge happens which could trigger the above ENOMEM errors. In addition the system would need to be under memory pressure. For example, we can't hit the above case in selftests because we missed having tests to merge skbs. (Added in later patch) To fix the below splat extend the rcu_read_lock/unnlock block to include the call to sk_psock_tls_verdict_apply(). This will fix both TLS redirect case and non-TLS redirect+error case. Also remove psock from the sk_psock_tls_verdict_apply() function signature its not used there. [ 1095.937597] WARNING: suspicious RCU usage [ 1095.940964] 5.7.0-rc7-02911-g463bac5f1ca79 #1 Tainted: G W [ 1095.944363] ----------------------------- [ 1095.947384] include/linux/skmsg.h:284 suspicious rcu_dereference_check() usage! [ 1095.950866] [ 1095.950866] other info that might help us debug this: [ 1095.950866] [ 1095.957146] [ 1095.957146] rcu_scheduler_active = 2, debug_locks = 1 [ 1095.961482] 1 lock held by test_sockmap/15970: [ 1095.964501] #0: ffff9ea6b25de660 (sk_lock-AF_INET){+.+.}-{0:0}, at: tls_sw_recvmsg+0x13a/0x840 [tls] [ 1095.968568] [ 1095.968568] stack backtrace: [ 1095.975001] CPU: 1 PID: 15970 Comm: test_sockmap Tainted: G W 5.7.0-rc7-02911-g463bac5f1ca79 #1 [ 1095.977883] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.12.0-1 04/01/2014 [ 1095.980519] Call Trace: [ 1095.982191] dump_stack+0x8f/0xd0 [ 1095.984040] sk_psock_skb_redirect+0xa6/0xf0 [ 1095.986073] sk_psock_tls_strp_read+0x1d8/0x250 [ 1095.988095] tls_sw_recvmsg+0x714/0x840 [tls] v2: Improve commit message to identify non-TLS redirect plus error case condition as well as more common TLS case. In the process I decided doing the rcu_read_unlock followed by the lock/unlock inside branches was unnecessarily complex. We can just extend the current rcu block and get the same effeective without the shuffling and branching. Thanks Martin! Fixes: e91de6afa81c1 ("bpf: Fix running sk_skb program types with ktls") Reported-by: Jakub Sitnicki Reported-by: kernel test robot Signed-off-by: John Fastabend Signed-off-by: Alexei Starovoitov Acked-by: Martin KaFai Lau Acked-by: Jakub Sitnicki Link: https://lore.kernel.org/bpf/159312677907.18340.11064813152758406626.stgit@john-XPS-13-9370 --- net/core/skmsg.c | 13 ++++++------- 1 file changed, 6 insertions(+), 7 deletions(-) diff --git a/net/core/skmsg.c b/net/core/skmsg.c index 351afbf6bfba..c41ab6906b21 100644 --- a/net/core/skmsg.c +++ b/net/core/skmsg.c @@ -683,7 +683,7 @@ static struct sk_psock *sk_psock_from_strp(struct strparser *strp) return container_of(parser, struct sk_psock, parser); } -static void sk_psock_skb_redirect(struct sk_psock *psock, struct sk_buff *skb) +static void sk_psock_skb_redirect(struct sk_buff *skb) { struct sk_psock *psock_other; struct sock *sk_other; @@ -715,12 +715,11 @@ static void sk_psock_skb_redirect(struct sk_psock *psock, struct sk_buff *skb) } } -static void sk_psock_tls_verdict_apply(struct sk_psock *psock, - struct sk_buff *skb, int verdict) +static void sk_psock_tls_verdict_apply(struct sk_buff *skb, int verdict) { switch (verdict) { case __SK_REDIRECT: - sk_psock_skb_redirect(psock, skb); + sk_psock_skb_redirect(skb); break; case __SK_PASS: case __SK_DROP: @@ -741,8 +740,8 @@ int sk_psock_tls_strp_read(struct sk_psock *psock, struct sk_buff *skb) ret = sk_psock_bpf_run(psock, prog, skb); ret = sk_psock_map_verd(ret, tcp_skb_bpf_redirect_fetch(skb)); } + sk_psock_tls_verdict_apply(skb, ret); rcu_read_unlock(); - sk_psock_tls_verdict_apply(psock, skb, ret); return ret; } EXPORT_SYMBOL_GPL(sk_psock_tls_strp_read); @@ -770,7 +769,7 @@ static void sk_psock_verdict_apply(struct sk_psock *psock, } goto out_free; case __SK_REDIRECT: - sk_psock_skb_redirect(psock, skb); + sk_psock_skb_redirect(skb); break; case __SK_DROP: /* fall-through */ @@ -794,8 +793,8 @@ static void sk_psock_strp_read(struct strparser *strp, struct sk_buff *skb) ret = sk_psock_bpf_run(psock, prog, skb); ret = sk_psock_map_verd(ret, tcp_skb_bpf_redirect_fetch(skb)); } - rcu_read_unlock(); sk_psock_verdict_apply(psock, skb, ret); + rcu_read_unlock(); } static int sk_psock_strp_read_done(struct strparser *strp, int err) -- cgit From 8025751d4d55a2f32be6bdf825b6a80c299875f5 Mon Sep 17 00:00:00 2001 From: John Fastabend Date: Thu, 25 Jun 2020 16:13:18 -0700 Subject: bpf, sockmap: RCU dereferenced psock may be used outside RCU block If an ingress verdict program specifies message sizes greater than skb->len and there is an ENOMEM error due to memory pressure we may call the rcv_msg handler outside the strp_data_ready() caller context. This is because on an ENOMEM error the strparser will retry from a workqueue. The caller currently protects the use of psock by calling the strp_data_ready() inside a rcu_read_lock/unlock block. But, in above workqueue error case the psock is accessed outside the read_lock/unlock block of the caller. So instead of using psock directly we must do a look up against the sk again to ensure the psock is available. There is an an ugly piece here where we must handle the case where we paused the strp and removed the psock. On psock removal we first pause the strparser and then remove the psock. If the strparser is paused while an skb is scheduled on the workqueue the skb will be dropped on the flow and kfree_skb() is called. If the workqueue manages to get called before we pause the strparser but runs the rcvmsg callback after the psock is removed we will hit the unlikely case where we run the sockmap rcvmsg handler but do not have a psock. For now we will follow strparser logic and drop the skb on the floor with skb_kfree(). This is ugly because the data is dropped. To date this has not caused problems in practice because either the application controlling the sockmap is coordinating with the datapath so that skbs are "flushed" before removal or we simply wait for the sock to be closed before removing it. This patch fixes the describe RCU bug and dropping the skb doesn't make things worse. Future patches will improve this by allowing the normal case where skbs are not merged to skip the strparser altogether. In practice many (most?) use cases have no need to merge skbs so its both a code complexity hit as seen above and a performance issue. For example, in the Cilium case we always set the strparser up to return sbks 1:1 without any merging and have avoided above issues. Fixes: e91de6afa81c1 ("bpf: Fix running sk_skb program types with ktls") Signed-off-by: John Fastabend Signed-off-by: Alexei Starovoitov Acked-by: Martin KaFai Lau Link: https://lore.kernel.org/bpf/159312679888.18340.15248924071966273998.stgit@john-XPS-13-9370 --- net/core/skmsg.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) diff --git a/net/core/skmsg.c b/net/core/skmsg.c index c41ab6906b21..6a32a1fd34f8 100644 --- a/net/core/skmsg.c +++ b/net/core/skmsg.c @@ -781,11 +781,18 @@ out_free: static void sk_psock_strp_read(struct strparser *strp, struct sk_buff *skb) { - struct sk_psock *psock = sk_psock_from_strp(strp); + struct sk_psock *psock; struct bpf_prog *prog; int ret = __SK_DROP; + struct sock *sk; rcu_read_lock(); + sk = strp->sk; + psock = sk_psock(sk); + if (unlikely(!psock)) { + kfree_skb(skb); + goto out; + } prog = READ_ONCE(psock->progs.skb_verdict); if (likely(prog)) { skb_orphan(skb); @@ -794,6 +801,7 @@ static void sk_psock_strp_read(struct strparser *strp, struct sk_buff *skb) ret = sk_psock_map_verd(ret, tcp_skb_bpf_redirect_fetch(skb)); } sk_psock_verdict_apply(psock, skb, ret); +out: rcu_read_unlock(); } -- cgit From 53792fa45b1b17f78f18bcd0bd167674341297e8 Mon Sep 17 00:00:00 2001 From: John Fastabend Date: Thu, 25 Jun 2020 16:13:38 -0700 Subject: bpf, sockmap: Add ingres skb tests that utilize merge skbs Add a test to check strparser merging skbs is working. Signed-off-by: John Fastabend Signed-off-by: Alexei Starovoitov Acked-by: Martin KaFai Lau Link: https://lore.kernel.org/bpf/159312681884.18340.4922800172600252370.stgit@john-XPS-13-9370 --- tools/testing/selftests/bpf/progs/test_sockmap_kern.h | 8 +++++++- tools/testing/selftests/bpf/test_sockmap.c | 18 ++++++++++++++++++ 2 files changed, 25 insertions(+), 1 deletion(-) diff --git a/tools/testing/selftests/bpf/progs/test_sockmap_kern.h b/tools/testing/selftests/bpf/progs/test_sockmap_kern.h index 057036ca1111..3dca4c2e2418 100644 --- a/tools/testing/selftests/bpf/progs/test_sockmap_kern.h +++ b/tools/testing/selftests/bpf/progs/test_sockmap_kern.h @@ -79,7 +79,7 @@ struct { struct { __uint(type, BPF_MAP_TYPE_ARRAY); - __uint(max_entries, 2); + __uint(max_entries, 3); __type(key, int); __type(value, int); } sock_skb_opts SEC(".maps"); @@ -94,6 +94,12 @@ struct { SEC("sk_skb1") int bpf_prog1(struct __sk_buff *skb) { + int *f, two = 2; + + f = bpf_map_lookup_elem(&sock_skb_opts, &two); + if (f && *f) { + return *f; + } return skb->len; } diff --git a/tools/testing/selftests/bpf/test_sockmap.c b/tools/testing/selftests/bpf/test_sockmap.c index 37695fc8096a..78789b27e573 100644 --- a/tools/testing/selftests/bpf/test_sockmap.c +++ b/tools/testing/selftests/bpf/test_sockmap.c @@ -85,6 +85,7 @@ int txmsg_ktls_skb_drop; int txmsg_ktls_skb_redir; int ktls; int peek_flag; +int skb_use_parser; static const struct option long_options[] = { {"help", no_argument, NULL, 'h' }, @@ -174,6 +175,7 @@ static void test_reset(void) txmsg_apply = txmsg_cork = 0; txmsg_ingress = txmsg_redir_skb = 0; txmsg_ktls_skb = txmsg_ktls_skb_drop = txmsg_ktls_skb_redir = 0; + skb_use_parser = 0; } static int test_start_subtest(const struct _test *t, struct sockmap_options *o) @@ -1211,6 +1213,11 @@ run: } } + if (skb_use_parser) { + i = 2; + err = bpf_map_update_elem(map_fd[7], &i, &skb_use_parser, BPF_ANY); + } + if (txmsg_drop) options->drop_expected = true; @@ -1650,6 +1657,16 @@ static void test_txmsg_cork(int cgrp, struct sockmap_options *opt) test_send(opt, cgrp); } +static void test_txmsg_ingress_parser(int cgrp, struct sockmap_options *opt) +{ + txmsg_pass = 1; + skb_use_parser = 512; + opt->iov_length = 256; + opt->iov_count = 1; + opt->rate = 2; + test_exec(cgrp, opt); +} + char *map_names[] = { "sock_map", "sock_map_txmsg", @@ -1748,6 +1765,7 @@ struct _test test[] = { {"txmsg test pull-data", test_txmsg_pull}, {"txmsg test pop-data", test_txmsg_pop}, {"txmsg test push/pop data", test_txmsg_push_pop}, + {"txmsg text ingress parser", test_txmsg_ingress_parser}, }; static int check_whitelist(struct _test *t, struct sockmap_options *opt) -- cgit