Re: [PATCH v2 bpf-next 02/15] bpf: net: Avoid sk_setsockopt() taking sk lock when called from bpf
From: Andrii Nakryiko <hidden>
Date: 2022-08-04 19:03:21
On Wed, Aug 3, 2022 at 1:49 PM Martin KaFai Lau [off-list ref] wrote:
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Most of the code in bpf_setsockopt(SOL_SOCKET) are duplicated from the sk_setsockopt(). The number of supported optnames are increasing ever and so as the duplicated code. One issue in reusing sk_setsockopt() is that the bpf prog has already acquired the sk lock. This patch adds a in_bpf() to tell if the sk_setsockopt() is called from a bpf prog. The bpf prog calling bpf_setsockopt() is either running in_task() or in_serving_softirq(). Both cases have the current->bpf_ctx initialized. Thus, the in_bpf() only needs to test !!current->bpf_ctx. This patch also adds sockopt_{lock,release}_sock() helpers for sk_setsockopt() to use. These helpers will test in_bpf() before acquiring/releasing the lock. They are in EXPORT_SYMBOL for the ipv6 module to use in a latter patch. Note on the change in sock_setbindtodevice(). sockopt_lock_sock() is done in sock_setbindtodevice() instead of doing the lock_sock in sock_bindtoindex(..., lock_sk = true). Signed-off-by: Martin KaFai Lau <redacted> --- include/linux/bpf.h | 8 ++++++++ include/net/sock.h | 3 +++ net/core/sock.c | 26 +++++++++++++++++++++++--- 3 files changed, 34 insertions(+), 3 deletions(-)diff --git a/include/linux/bpf.h b/include/linux/bpf.h index 20c26aed7896..b905b1b34fe4 100644 --- a/include/linux/bpf.h +++ b/include/linux/bpf.h@@ -1966,6 +1966,10 @@ static inline bool unprivileged_ebpf_enabled(void) return !sysctl_unprivileged_bpf_disabled; } +static inline bool in_bpf(void)
I think this function deserves a big comment explaining that it's not 100% accurate, as not every BPF program type sets bpf_ctx. As it is named in_bpf() promises a lot more generality than it actually provides. Should this be named either more specific has_current_bpf_ctx() maybe? Also, separately, should be make an effort to set bpf_ctx for all program types (instead or in addition to the above)?
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+{ + return !!current->bpf_ctx; +} #else /* !CONFIG_BPF_SYSCALL */ static inline struct bpf_prog *bpf_prog_get(u32 ufd) {@@ -2175,6 +2179,10 @@ static inline bool unprivileged_ebpf_enabled(void) return false; } +static inline bool in_bpf(void) +{ + return false; +} #endif /* CONFIG_BPF_SYSCALL */ void __bpf_free_used_btfs(struct bpf_prog_aux *aux,diff --git a/include/net/sock.h b/include/net/sock.h index a7273b289188..b2ff230860c6 100644 --- a/include/net/sock.h +++ b/include/net/sock.h@@ -1721,6 +1721,9 @@ static inline void unlock_sock_fast(struct sock *sk, bool slow) } } +void sockopt_lock_sock(struct sock *sk); +void sockopt_release_sock(struct sock *sk); + /* Used by processes to "lock" a socket state, so that * interrupts and bottom half handlers won't change it * from under us. It essentially blocks any incomingdiff --git a/net/core/sock.c b/net/core/sock.c index 20269c37ab3b..82759540ae2c 100644 --- a/net/core/sock.c +++ b/net/core/sock.c@@ -703,7 +703,9 @@ static int sock_setbindtodevice(struct sock *sk, sockptr_t optval, int optlen) goto out; } - return sock_bindtoindex(sk, index, true); + sockopt_lock_sock(sk); + ret = sock_bindtoindex_locked(sk, index); + sockopt_release_sock(sk); out: #endif@@ -1036,6 +1038,24 @@ static int sock_reserve_memory(struct sock *sk, int bytes) return 0; } +void sockopt_lock_sock(struct sock *sk) +{ + if (in_bpf()) + return; + + lock_sock(sk); +} +EXPORT_SYMBOL(sockopt_lock_sock); + +void sockopt_release_sock(struct sock *sk) +{ + if (in_bpf()) + return; + + release_sock(sk); +} +EXPORT_SYMBOL(sockopt_release_sock); + /* * This is meant for all protocols to use and covers goings on * at the socket level. Everything here is generic.@@ -1067,7 +1087,7 @@ static int sk_setsockopt(struct sock *sk, int level, int optname, valbool = val ? 1 : 0; - lock_sock(sk); + sockopt_lock_sock(sk); switch (optname) { case SO_DEBUG:@@ -1496,7 +1516,7 @@ static int sk_setsockopt(struct sock *sk, int level, int optname, ret = -ENOPROTOOPT; break; } - release_sock(sk); + sockopt_release_sock(sk); return ret; } --2.30.2