Re: [PATCH] perf: fix use after free of perf_trace_buf

From: Jiri Olsa
Date: Tue Mar 19 2019 - 09:38:03 EST

On Tue, Mar 19, 2019 at 05:51:00PM +0530, Prateek Sood wrote:
> SyS_perf_event_open()
> free_event()
> _free_event()
> tp_perf_event_destroy()
> perf_trace_destroy()
> perf_trace_event_unreg() //free perf_trace_buf
>
> trace_cpu_frequency()
> perf_trace_cpu()
> perf_trace_buf_alloc() //access perf_trace_buf
>
> CPU0 CPU1
> perf_trace_event_unreg() perf_trace_cpu()
> head = (event_call->perf_events)
>
> free_percpu(tp_event->perf_events)
> tp_event->perf_events = NULL
> --total_ref_count
> free_percpu(perf_trace_buf[i])
> perf_trace_buf[i] = NULL
>
> raw_data = perf_trace_buf[rctx]
> memset(raw_data)
>
> A potential race exists between access of perf_trace_buf from

so there's no actual backtrace of the crash, right?

jirka

> perf_trace_buf_alloc() and perf_trace_event_unreg(). This can
> result in perf_trace_buf[rctx] being NULL during access from memset()
> in perf_trace_buf_alloc().
>
> Change-Id: I95ae774b9fcc653aa808f2d9f3e4359b3605e909
> Signed-off-by: Prateek Sood <prsood@xxxxxxxxxxxxxx>
> ---
> include/linux/trace_events.h | 2 ++
> include/trace/perf.h | 5 +++-
> kernel/trace/trace_event_perf.c | 63 ++++++++++++++++++++++++++++++++++-------
> kernel/trace/trace_kprobe.c | 10 +++++--
> kernel/trace/trace_syscalls.c | 14 ++++++---
> kernel/trace/trace_uprobe.c | 2 ++
> 6 files changed, 79 insertions(+), 17 deletions(-)
>
> diff --git a/include/linux/trace_events.h b/include/linux/trace_events.h
> index 8a62731..dbdad19 100644
> --- a/include/linux/trace_events.h
> +++ b/include/linux/trace_events.h
> @@ -591,6 +591,8 @@ extern int ftrace_profile_set_filter(struct perf_event *event, int event_id,
> extern void ftrace_profile_free_filter(struct perf_event *event);
> void perf_trace_buf_update(void *record, u16 type);
> void *perf_trace_buf_alloc(int size, struct pt_regs **regs, int *rctxp);
> +void get_perf_trace_buf(void);
> +void put_perf_trace_buf(void);
>
> void bpf_trace_run1(struct bpf_prog *prog, u64 arg1);
> void bpf_trace_run2(struct bpf_prog *prog, u64 arg1, u64 arg2);
> diff --git a/include/trace/perf.h b/include/trace/perf.h
> index dbc6c74..f808c33 100644
> --- a/include/trace/perf.h
> +++ b/include/trace/perf.h
> @@ -55,9 +55,10 @@
> sizeof(u64)); \
> __entry_size -= sizeof(u32); \
> \
> + get_perf_trace_buf(); \
> entry = perf_trace_buf_alloc(__entry_size, &__regs, &rctx); \
> if (!entry) \
> - return; \
> + goto out; \
> \
> perf_fetch_caller_regs(__regs); \
> \
> @@ -68,6 +69,8 @@
> perf_trace_run_bpf_submit(entry, __entry_size, rctx, \
> event_call, __count, __regs, \
> head, __task); \
> +out: \
> + put_perf_trace_buf(); \
> }
>
> /*
> diff --git a/kernel/trace/trace_event_perf.c b/kernel/trace/trace_event_perf.c
> index 4629a61..6caca88 100644
> --- a/kernel/trace/trace_event_perf.c
> +++ b/kernel/trace/trace_event_perf.c
> @@ -21,7 +21,8 @@ typedef typeof(unsigned long [PERF_MAX_TRACE_SIZE / sizeof(unsigned long)])
> perf_trace_t;
>
> /* Count the events in use (per event id, not per instance) */
> -static int total_ref_count;
> +static int alloc_ref_count;
> +static atomic_t access_ref_count[PERF_NR_CONTEXTS];
>
> static int perf_trace_event_perm(struct trace_event_call *tp_event,
> struct perf_event *p_event)
> @@ -88,6 +89,34 @@ static int perf_trace_event_perm(struct trace_event_call *tp_event,
> return 0;
> }
>
> +void get_perf_trace_buf(void)
> +{
> + int rctx;
> +
> + rctx = perf_swevent_get_recursion_context();
> + if (rctx < 0)
> + return;
> +
> + atomic_inc(&access_ref_count[rctx]);
> + perf_swevent_put_recursion_context(rctx);
> +}
> +EXPORT_SYMBOL_GPL(get_perf_trace_buf);
> +NOKPROBE_SYMBOL(get_perf_trace_buf);
> +
> +void put_perf_trace_buf(void)
> +{
> + int rctx;
> +
> + rctx = perf_swevent_get_recursion_context();
> + if (rctx < 0)
> + return;
> +
> + atomic_dec(&access_ref_count[rctx]);
> + perf_swevent_put_recursion_context(rctx);
> +}
> +EXPORT_SYMBOL_GPL(put_perf_trace_buf);
> +NOKPROBE_SYMBOL(put_perf_trace_buf);
> +
> static int perf_trace_event_reg(struct trace_event_call *tp_event,
> struct perf_event *p_event)
> {
> @@ -108,7 +137,7 @@ static int perf_trace_event_reg(struct trace_event_call *tp_event,
>
> tp_event->perf_events = list;
>
> - if (!total_ref_count) {
> + if (!alloc_ref_count) {
> char __percpu *buf;
> int i;
>
> @@ -125,11 +154,11 @@ static int perf_trace_event_reg(struct trace_event_call *tp_event,
> if (ret)
> goto fail;
>
> - total_ref_count++;
> + alloc_ref_count++;
> return 0;
>
> fail:
> - if (!total_ref_count) {
> + if (!alloc_ref_count) {
> int i;
>
> for (i = 0; i < PERF_NR_CONTEXTS; i++) {
> @@ -150,6 +179,7 @@ static void perf_trace_event_unreg(struct perf_event *p_event)
> {
> struct trace_event_call *tp_event = p_event->tp_event;
> int i;
> + bool retry;
>
> if (--tp_event->perf_refcount > 0)
> goto out;
> @@ -165,10 +195,21 @@ static void perf_trace_event_unreg(struct perf_event *p_event)
> free_percpu(tp_event->perf_events);
> tp_event->perf_events = NULL;
>
> - if (!--total_ref_count) {
> - for (i = 0; i < PERF_NR_CONTEXTS; i++) {
> - free_percpu(perf_trace_buf[i]);
> - perf_trace_buf[i] = NULL;
> + if (!--alloc_ref_count) {
> +again:
> + retry = false;
> + for (i = 0; (i < PERF_NR_CONTEXTS) && perf_trace_buf[i]; i++) {
> + if (!atomic_read(&access_ref_count[i])) {
> + free_percpu(perf_trace_buf[i]);
> + perf_trace_buf[i] = NULL;
> + } else
> + retry = true;
> + }
> +
> + if (retry) {
> + set_current_state(TASK_INTERRUPTIBLE);
> + schedule_timeout(msecs_to_jiffies(1));
> + goto again;
> }
> }
> out:
> @@ -453,15 +494,17 @@ void perf_trace_buf_update(void *record, u16 type)
> memset(&regs, 0, sizeof(regs));
> perf_fetch_caller_regs(&regs);
>
> + get_perf_trace_buf();
> entry = perf_trace_buf_alloc(ENTRY_SIZE, NULL, &rctx);
> if (!entry)
> - return;
> + goto out;
>
> entry->ip = ip;
> entry->parent_ip = parent_ip;
> perf_trace_buf_submit(entry, ENTRY_SIZE, rctx, TRACE_FN,
> 1, &regs, &head, NULL);
> -
> +out:
> + put_perf_trace_buf();
> #undef ENTRY_SIZE
> }
>
> diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
> index 5d5129b..7830190 100644
> --- a/kernel/trace/trace_kprobe.c
> +++ b/kernel/trace/trace_kprobe.c
> @@ -1166,15 +1166,18 @@ static int kretprobe_event_define_fields(struct trace_event_call *event_call)
> size = ALIGN(__size + sizeof(u32), sizeof(u64));
> size -= sizeof(u32);
>
> + get_perf_trace_buf();
> entry = perf_trace_buf_alloc(size, NULL, &rctx);
> if (!entry)
> - return 0;
> + goto out;
>
> entry->ip = (unsigned long)tk->rp.kp.addr;
> memset(&entry[1], 0, dsize);
> store_trace_args(&entry[1], &tk->tp, regs, sizeof(*entry), dsize);
> perf_trace_buf_submit(entry, size, rctx, call->event.type, 1, regs,
> head, NULL);
> +out:
> + put_perf_trace_buf();
> return 0;
> }
> NOKPROBE_SYMBOL(kprobe_perf_func);
> @@ -1202,15 +1205,18 @@ static int kretprobe_event_define_fields(struct trace_event_call *event_call)
> size = ALIGN(__size + sizeof(u32), sizeof(u64));
> size -= sizeof(u32);
>
> + get_perf_trace_buf();
> entry = perf_trace_buf_alloc(size, NULL, &rctx);
> if (!entry)
> - return;
> + goto out;
>
> entry->func = (unsigned long)tk->rp.kp.addr;
> entry->ret_ip = (unsigned long)ri->ret_addr;
> store_trace_args(&entry[1], &tk->tp, regs, sizeof(*entry), dsize);
> perf_trace_buf_submit(entry, size, rctx, call->event.type, 1, regs,
> head, NULL);
> +out:
> + put_perf_trace_buf();
> }
> NOKPROBE_SYMBOL(kretprobe_perf_func);
>
> diff --git a/kernel/trace/trace_syscalls.c b/kernel/trace/trace_syscalls.c
> index f93a56d..a08110f 100644
> --- a/kernel/trace/trace_syscalls.c
> +++ b/kernel/trace/trace_syscalls.c
> @@ -608,9 +608,10 @@ static void perf_syscall_enter(void *ignore, struct pt_regs *regs, long id)
> size = ALIGN(size + sizeof(u32), sizeof(u64));
> size -= sizeof(u32);
>
> + get_perf_trace_buf();
> rec = perf_trace_buf_alloc(size, NULL, &rctx);
> if (!rec)
> - return;
> + goto out;
>
> rec->nr = syscall_nr;
> syscall_get_arguments(current, regs, 0, sys_data->nb_args,
> @@ -620,12 +621,14 @@ static void perf_syscall_enter(void *ignore, struct pt_regs *regs, long id)
> !perf_call_bpf_enter(sys_data->enter_event, regs, sys_data, rec)) ||
> hlist_empty(head)) {
> perf_swevent_put_recursion_context(rctx);
> - return;
> + goto out;
> }
>
> perf_trace_buf_submit(rec, size, rctx,
> sys_data->enter_event->event.type, 1, regs,
> head, NULL);
> +out:
> + put_perf_trace_buf();
> }
>
> static int perf_sysenter_enable(struct trace_event_call *call)
> @@ -706,9 +709,10 @@ static void perf_syscall_exit(void *ignore, struct pt_regs *regs, long ret)
> size = ALIGN(sizeof(*rec) + sizeof(u32), sizeof(u64));
> size -= sizeof(u32);
>
> + get_perf_trace_buf();
> rec = perf_trace_buf_alloc(size, NULL, &rctx);
> if (!rec)
> - return;
> + goto out;
>
> rec->nr = syscall_nr;
> rec->ret = syscall_get_return_value(current, regs);
> @@ -717,11 +721,13 @@ static void perf_syscall_exit(void *ignore, struct pt_regs *regs, long ret)
> !perf_call_bpf_exit(sys_data->exit_event, regs, rec)) ||
> hlist_empty(head)) {
> perf_swevent_put_recursion_context(rctx);
> - return;
> + goto out;
> }
>
> perf_trace_buf_submit(rec, size, rctx, sys_data->exit_event->event.type,
> 1, regs, head, NULL);
> +out:
> + put_perf_trace_buf();
> }
>
> static int perf_sysexit_enable(struct trace_event_call *call)
> diff --git a/kernel/trace/trace_uprobe.c b/kernel/trace/trace_uprobe.c
> index be78d99..c931b22 100644
> --- a/kernel/trace/trace_uprobe.c
> +++ b/kernel/trace/trace_uprobe.c
> @@ -1116,6 +1116,7 @@ static void __uprobe_perf_func(struct trace_uprobe *tu,
> if (hlist_empty(head))
> goto out;
>
> + get_perf_trace_buf();
> entry = perf_trace_buf_alloc(size, NULL, &rctx);
> if (!entry)
> goto out;
> @@ -1140,6 +1141,7 @@ static void __uprobe_perf_func(struct trace_uprobe *tu,
> perf_trace_buf_submit(entry, size, rctx, call->event.type, 1, regs,
> head, NULL);
> out:
> + put_perf_trace_buf();
> preempt_enable();
> }
>
> --
> Qualcomm India Private Limited, on behalf of Qualcomm Innovation Center, Inc.,
> is a member of Code Aurora Forum, a Linux Foundation Collaborative Project.
>