On bpf syscall map operations the bpf_disable_instrumentation function is called for the reason described in the comment to the function. The description matches the bug case. The function increments a per CPU integer variable bpf_prog_active. The variable is not processed in the bpf trace path. The fix implements a similar processing as for kprobe handling. The fix degrades the bpf tracing by skipping some eBPF trace sequences that otherwise might yield deadlock.
Reported-by: syzbot+9d95beb2a3c260622...@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=9d95beb2a3c260622518 Link: https://lore.kernel.org/all/000000000000adb08b0614139...@google.com/T/ Signed-off-by: Wojciech Gładysz <wojciech.glad...@infogain.com> --- kernel/trace/bpf_trace.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c index 6249dac61701..8de2e084b162 100644 --- a/kernel/trace/bpf_trace.c +++ b/kernel/trace/bpf_trace.c @@ -2391,7 +2391,9 @@ void __bpf_trace_run(struct bpf_raw_tp_link *link, u64 *args) struct bpf_trace_run_ctx run_ctx; cant_sleep(); - if (unlikely(this_cpu_inc_return(*(prog->active)) != 1)) { + + // if the instrumentation is not disabled disable recurrence and go + if (unlikely(__this_cpu_inc_return(bpf_prog_active) != 1)) { bpf_prog_inc_misses_counter(prog); goto out; } @@ -2405,7 +2407,7 @@ void __bpf_trace_run(struct bpf_raw_tp_link *link, u64 *args) bpf_reset_run_ctx(old_run_ctx); out: - this_cpu_dec(*(prog->active)); + __this_cpu_dec(bpf_prog_active); } #define UNPACK(...) __VA_ARGS__ -- 2.35.3
