Fix multiple data races involving event->prog field: 1. __perf_event_overflow() reads event->prog twice without synchronization creating a TOCTOU race. Fix by using READ_ONCE() to capture prog into a local variable and pass it directly to bpf_overflow_handler() to avoid a second read inside that function.
2. perf_event_set_bpf_handler() and perf_event_free_bpf_handler() perform plain writes to event->prog without WRITE_ONCE(), failing to pair with the READ_ONCE() in __perf_event_overflow(). Fix by using WRITE_ONCE() in all write paths including perf_event_detach_bpf_prog(). 3. perf_event_alloc() reads parent_event->prog locklessly during fork() which can race with a concurrent detach clearing and freeing the prog, potentially causing a NULL pointer dereference or use-after-free in bpf_prog_inc(). Fix by holding bpf_event_mutex when inheriting the BPF program. Make bpf_event_mutex non-static and declare it extern in perf_event.h so it is accessible from kernel/events/core.c. Reported-by: [email protected] Closes: https://syzkaller.appspot.com/bug?extid=651d2774bd1d8395595f Link: https://lore.kernel.org/all/[email protected]/T/ [v1] Signed-off-by: Deepanshu Kartikey <[email protected]> --- v2: - Pass validated prog pointer directly to bpf_overflow_handler() to avoid TOCTOU race from second READ_ONCE() inside the handler - Add WRITE_ONCE() to perf_event_set_bpf_handler() and perf_event_free_bpf_handler() to pair with READ_ONCE() in overflow - Fix lockless access in perf_event_alloc() during fork() by holding bpf_event_mutex to prevent concurrent detach UAF - Make bpf_event_mutex non-static and export via perf_event.h --- include/linux/perf_event.h | 2 ++ kernel/events/core.c | 23 +++++++++++++---------- kernel/trace/bpf_trace.c | 4 ++-- 3 files changed, 17 insertions(+), 12 deletions(-) diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h index 48d851fbd8ea..5c6dabb6dccb 100644 --- a/include/linux/perf_event.h +++ b/include/linux/perf_event.h @@ -2136,4 +2136,6 @@ static inline void perf_lopwr_cb(bool mode) } #endif +extern struct mutex bpf_event_mutex; + #endif /* _LINUX_PERF_EVENT_H */ diff --git a/kernel/events/core.c b/kernel/events/core.c index ba5bd6a78fe7..6f8d3b57fa01 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -10652,20 +10652,19 @@ static inline bool sample_is_allowed(struct perf_event *event, struct pt_regs *r #ifdef CONFIG_BPF_SYSCALL static int bpf_overflow_handler(struct perf_event *event, struct perf_sample_data *data, - struct pt_regs *regs) + struct pt_regs *regs, + struct bpf_prog *prog) { struct bpf_perf_event_data_kern ctx = { .data = data, .event = event, }; - struct bpf_prog *prog; int ret = 0; ctx.regs = perf_arch_bpf_user_pt_regs(regs); if (unlikely(__this_cpu_inc_return(bpf_prog_active) != 1)) goto out; rcu_read_lock(); - prog = READ_ONCE(event->prog); if (prog) { perf_prepare_sample(data, event, regs); ret = bpf_prog_run(prog, &ctx); @@ -10708,7 +10707,7 @@ static inline int perf_event_set_bpf_handler(struct perf_event *event, return -EPROTO; } - event->prog = prog; + WRITE_ONCE(event->prog, prog); event->bpf_cookie = bpf_cookie; return 0; } @@ -10720,7 +10719,7 @@ static inline void perf_event_free_bpf_handler(struct perf_event *event) if (!prog) return; - event->prog = NULL; + WRITE_ONCE(event->prog, NULL); bpf_prog_put(prog); } #else @@ -10753,6 +10752,7 @@ static int __perf_event_overflow(struct perf_event *event, { int events = atomic_read(&event->event_limit); int ret = 0; + struct bpf_prog *prog; /* * Non-sampling counters might still use the PMI to fold short @@ -10766,8 +10766,9 @@ static int __perf_event_overflow(struct perf_event *event, if (event->attr.aux_pause) perf_event_aux_pause(event->aux_event, true); - if (event->prog && event->prog->type == BPF_PROG_TYPE_PERF_EVENT && - !bpf_overflow_handler(event, data, regs)) + prog = READ_ONCE(event->prog); + if (prog && prog->type == BPF_PROG_TYPE_PERF_EVENT && + !bpf_overflow_handler(event, data, regs, prog)) goto out; /* @@ -13433,12 +13434,15 @@ perf_event_alloc(struct perf_event_attr *attr, int cpu, overflow_handler = parent_event->overflow_handler; context = parent_event->overflow_handler_context; #if defined(CONFIG_BPF_SYSCALL) && defined(CONFIG_EVENT_TRACING) - if (parent_event->prog) { - struct bpf_prog *prog = parent_event->prog; - + struct bpf_prog *prog; + + mutex_lock(&bpf_event_mutex); + prog = parent_event->prog; + if (prog) { bpf_prog_inc(prog); event->prog = prog; } + mutex_unlock(&bpf_event_mutex); #endif } diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c index 75495a5c3507..026b5c492115 100644 --- a/kernel/trace/bpf_trace.c +++ b/kernel/trace/bpf_trace.c @@ -1944,7 +1944,7 @@ const struct bpf_verifier_ops perf_event_verifier_ops = { const struct bpf_prog_ops perf_event_prog_ops = { }; -static DEFINE_MUTEX(bpf_event_mutex); +DEFINE_MUTEX(bpf_event_mutex); #define BPF_TRACE_MAX_PROGS 64 @@ -2018,7 +2018,7 @@ void perf_event_detach_bpf_prog(struct perf_event *event) put: prog = event->prog; - event->prog = NULL; + WRITE_ONCE(event->prog, NULL); unlock: mutex_unlock(&bpf_event_mutex); -- 2.43.0
