bpf, perf: delay release of BPF prog after grace period

[ Upstream commit ceb56070359b7329b5678b5d95a376fcb24767be ]

Commit dead9f29ddcc ("perf: Fix race in BPF program unregister") moved
destruction of BPF program from free_event_rcu() callback to __free_event(),
which is problematic if used with tail calls: if prog A is attached as
trace event directly, but at the same time present in a tail call map used
by another trace event program elsewhere, then we need to delay destruction
via RCU grace period since it can still be in use by the program doing the
tail call (the prog first needs to be dropped from the tail call map, then
trace event with prog A attached destroyed, so we get immediate destruction).

Fixes: dead9f29ddcc ("perf: Fix race in BPF program unregister")
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Cc: Jann Horn <jann@thejh.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 67bc2da5d2336b7c7c77cb18069b514f2e4b1239..4f6d29c8e3d865621deddd85937d4449fa118958 100644 (file)
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -198,6 +198,10 @@ static inline struct bpf_prog *bpf_prog_get(u32 ufd)
 static inline void bpf_prog_put(struct bpf_prog *prog)
 {
 }
+
+static inline void bpf_prog_put_rcu(struct bpf_prog *prog)
+{
+}
 #endif /* CONFIG_BPF_SYSCALL */
 
 /* verifier prototypes for helper functions called from eBPF programs */

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 95e47d2f2c67505708513e774e2463c1c9dfb4ff..12ecd4f0329fcb6532eb6391ac8984a9a2e901b3 100644 (file)
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -7101,7 +7101,7 @@ static void perf_event_free_bpf_prog(struct perf_event *event)
        prog = event->tp_event->prog;
        if (prog) {
                event->tp_event->prog = NULL;
-               bpf_prog_put(prog);
+               bpf_prog_put_rcu(prog);
        }
 }