Re: [PATCH v3 bpf-next 02/15] bpf: net: Avoid sk_setsockopt() taking sk lock when called from bpf

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
has_current_bpf_ctx() 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 has_current_bpf_ctx() 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
has_current_bpf_ctx() 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 | 14 ++++++++++++++
 include/net/sock.h  |  3 +++
 net/core/sock.c     | 30 +++++++++++++++++++++++++++---
 3 files changed, 44 insertions(+), 3 deletions(-)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index a627a02cf8ab..0a600b2013cc 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h

@@ -1966,6 +1966,16 @@ static inline bool unprivileged_ebpf_enabled(void)
        return !sysctl_unprivileged_bpf_disabled;
 }

+/* Not all bpf prog type has the bpf_ctx.
+ * Only trampoline and cgroup-bpf have it.