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SubjectRe: [PATCH] bpf: don't fail kmalloc while releasing raw_tp
On Sat, 14 Nov 2020 21:52:55 -0800
Matt Mullins <mmullins@mmlx.us> wrote:

> bpf_link_free is always called in process context, including from a
> workqueue and from __fput. Neither of these have the ability to
> propagate an -ENOMEM to the caller.
>

Hmm, I think the real fix is to not have unregistering a tracepoint probe
fail because of allocation. We are removing a probe, perhaps we could just
inject NULL pointer that gets checked via the DO_TRACE loop?

I bet failing an unregister because of an allocation failure causes
problems elsewhere than just BPF.

Mathieu,

Can't we do something that would still allow to unregister a probe even if
a new probe array fails to allocate? We could kick off a irq work to try to
clean up the probe at a later time, but still, the unregister itself should
not fail due to memory failure.

-- Steve



> Reported-by: syzbot+83aa762ef23b6f0d1991@syzkaller.appspotmail.com
> Reported-by: syzbot+d29e58bb557324e55e5e@syzkaller.appspotmail.com
> Signed-off-by: Matt Mullins <mmullins@mmlx.us>
> ---
> I previously referenced a "pretty ugly" patch. This is not that one,
> because I don't think there's any way I can make the caller of
> ->release() actually handle errors like ENOMEM.
>
> It also looks like most of the other ways tracepoint_probe_unregister is
> called also don't check the error code (e.g. just a quick grep found
> blk_unregister_tracepoints). Should this just be upgraded to GFP_NOFAIL
> across the board instead of passing around a gfp_t?
>
> include/linux/trace_events.h | 6 ++++--
> include/linux/tracepoint.h | 7 +++++--
> kernel/bpf/syscall.c | 2 +-
> kernel/trace/bpf_trace.c | 6 ++++--
> kernel/trace/trace_events.c | 6 ++++--
> kernel/tracepoint.c | 20 ++++++++++----------
> 6 files changed, 28 insertions(+), 19 deletions(-)
>
> diff --git a/include/linux/trace_events.h b/include/linux/trace_events.h
> index 5c6943354049..166ad7646a98 100644
> --- a/include/linux/trace_events.h
> +++ b/include/linux/trace_events.h
> @@ -625,7 +625,8 @@ int perf_event_attach_bpf_prog(struct perf_event *event, struct bpf_prog *prog);
> void perf_event_detach_bpf_prog(struct perf_event *event);
> int perf_event_query_prog_array(struct perf_event *event, void __user *info);
> int bpf_probe_register(struct bpf_raw_event_map *btp, struct bpf_prog *prog);
> -int bpf_probe_unregister(struct bpf_raw_event_map *btp, struct bpf_prog *prog);
> +int bpf_probe_unregister(struct bpf_raw_event_map *btp, struct bpf_prog *prog,
> + gfp_t flags);
> struct bpf_raw_event_map *bpf_get_raw_tracepoint(const char *name);
> void bpf_put_raw_tracepoint(struct bpf_raw_event_map *btp);
> int bpf_get_perf_event_info(const struct perf_event *event, u32 *prog_id,
> @@ -654,7 +655,8 @@ static inline int bpf_probe_register(struct bpf_raw_event_map *btp, struct bpf_p
> {
> return -EOPNOTSUPP;
> }
> -static inline int bpf_probe_unregister(struct bpf_raw_event_map *btp, struct bpf_prog *p)
> +static inline int bpf_probe_unregister(struct bpf_raw_event_map *btp,
> + struct bpf_prog *p, gfp_t flags)
> {
> return -EOPNOTSUPP;
> }
> diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h
> index 598fec9f9dbf..7b02f92f3b8f 100644
> --- a/include/linux/tracepoint.h
> +++ b/include/linux/tracepoint.h
> @@ -12,6 +12,7 @@
> * Heavily inspired from the Linux Kernel Markers.
> */
>
> +#include <linux/gfp.h>
> #include <linux/smp.h>
> #include <linux/srcu.h>
> #include <linux/errno.h>
> @@ -40,7 +41,8 @@ extern int
> tracepoint_probe_register_prio(struct tracepoint *tp, void *probe, void *data,
> int prio);
> extern int
> -tracepoint_probe_unregister(struct tracepoint *tp, void *probe, void *data);
> +tracepoint_probe_unregister(struct tracepoint *tp, void *probe, void *data,
> + gfp_t flags);
> extern void
> for_each_kernel_tracepoint(void (*fct)(struct tracepoint *tp, void *priv),
> void *priv);
> @@ -260,7 +262,8 @@ static inline struct tracepoint *tracepoint_ptr_deref(tracepoint_ptr_t *p)
> unregister_trace_##name(void (*probe)(data_proto), void *data) \
> { \
> return tracepoint_probe_unregister(&__tracepoint_##name,\
> - (void *)probe, data); \
> + (void *)probe, data, \
> + GFP_KERNEL); \
> } \
> static inline void \
> check_trace_callback_type_##name(void (*cb)(data_proto)) \
> diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> index b999e7ff2583..f6876681c4ab 100644
> --- a/kernel/bpf/syscall.c
> +++ b/kernel/bpf/syscall.c
> @@ -2601,7 +2601,7 @@ static void bpf_raw_tp_link_release(struct bpf_link *link)
> struct bpf_raw_tp_link *raw_tp =
> container_of(link, struct bpf_raw_tp_link, link);
>
> - bpf_probe_unregister(raw_tp->btp, raw_tp->link.prog);
> + bpf_probe_unregister(raw_tp->btp, raw_tp->link.prog, GFP_KERNEL | __GFP_NOFAIL);
> bpf_put_raw_tracepoint(raw_tp->btp);
> }
>
> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> index a8d4f253ed77..a4ea58c7506d 100644
> --- a/kernel/trace/bpf_trace.c
> +++ b/kernel/trace/bpf_trace.c
> @@ -1955,9 +1955,11 @@ int bpf_probe_register(struct bpf_raw_event_map *btp, struct bpf_prog *prog)
> return __bpf_probe_register(btp, prog);
> }
>
> -int bpf_probe_unregister(struct bpf_raw_event_map *btp, struct bpf_prog *prog)
> +int bpf_probe_unregister(struct bpf_raw_event_map *btp, struct bpf_prog *prog,
> + gfp_t flags)
> {
> - return tracepoint_probe_unregister(btp->tp, (void *)btp->bpf_func, prog);
> + return tracepoint_probe_unregister(btp->tp, (void *)btp->bpf_func, prog,
> + flags);
> }
>
> int bpf_get_perf_event_info(const struct perf_event *event, u32 *prog_id,
> diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
> index a85effb2373b..ab1ac89caed2 100644
> --- a/kernel/trace/trace_events.c
> +++ b/kernel/trace/trace_events.c
> @@ -296,7 +296,8 @@ int trace_event_reg(struct trace_event_call *call,
> case TRACE_REG_UNREGISTER:
> tracepoint_probe_unregister(call->tp,
> call->class->probe,
> - file);
> + file,
> + GFP_KERNEL);
> return 0;
>
> #ifdef CONFIG_PERF_EVENTS
> @@ -307,7 +308,8 @@ int trace_event_reg(struct trace_event_call *call,
> case TRACE_REG_PERF_UNREGISTER:
> tracepoint_probe_unregister(call->tp,
> call->class->perf_probe,
> - call);
> + call,
> + GFP_KERNEL);
> return 0;
> case TRACE_REG_PERF_OPEN:
> case TRACE_REG_PERF_CLOSE:
> diff --git a/kernel/tracepoint.c b/kernel/tracepoint.c
> index 73956eaff8a9..619666a43c9f 100644
> --- a/kernel/tracepoint.c
> +++ b/kernel/tracepoint.c
> @@ -53,10 +53,9 @@ struct tp_probes {
> struct tracepoint_func probes[0];
> };
>
> -static inline void *allocate_probes(int count)
> +static inline void *allocate_probes(int count, gfp_t flags)
> {
> - struct tp_probes *p = kmalloc(struct_size(p, probes, count),
> - GFP_KERNEL);
> + struct tp_probes *p = kmalloc(struct_size(p, probes, count), flags);
> return p == NULL ? NULL : p->probes;
> }
>
> @@ -150,7 +149,7 @@ func_add(struct tracepoint_func **funcs, struct tracepoint_func *tp_func,
> }
> }
> /* + 2 : one for new probe, one for NULL func */
> - new = allocate_probes(nr_probes + 2);
> + new = allocate_probes(nr_probes + 2, GFP_KERNEL);
> if (new == NULL)
> return ERR_PTR(-ENOMEM);
> if (old) {
> @@ -174,7 +173,7 @@ func_add(struct tracepoint_func **funcs, struct tracepoint_func *tp_func,
> }
>
> static void *func_remove(struct tracepoint_func **funcs,
> - struct tracepoint_func *tp_func)
> + struct tracepoint_func *tp_func, gfp_t flags)
> {
> int nr_probes = 0, nr_del = 0, i;
> struct tracepoint_func *old, *new;
> @@ -207,7 +206,7 @@ static void *func_remove(struct tracepoint_func **funcs,
> int j = 0;
> /* N -> M, (N > 1, M > 0) */
> /* + 1 for NULL */
> - new = allocate_probes(nr_probes - nr_del + 1);
> + new = allocate_probes(nr_probes - nr_del + 1, flags);
> if (new == NULL)
> return ERR_PTR(-ENOMEM);
> for (i = 0; old[i].func; i++)
> @@ -264,13 +263,13 @@ static int tracepoint_add_func(struct tracepoint *tp,
> * by preempt_disable around the call site.
> */
> static int tracepoint_remove_func(struct tracepoint *tp,
> - struct tracepoint_func *func)
> + struct tracepoint_func *func, gfp_t flags)
> {
> struct tracepoint_func *old, *tp_funcs;
>
> tp_funcs = rcu_dereference_protected(tp->funcs,
> lockdep_is_held(&tracepoints_mutex));
> - old = func_remove(&tp_funcs, func);
> + old = func_remove(&tp_funcs, func, flags);
> if (IS_ERR(old)) {
> WARN_ON_ONCE(PTR_ERR(old) != -ENOMEM);
> return PTR_ERR(old);
> @@ -344,7 +343,8 @@ EXPORT_SYMBOL_GPL(tracepoint_probe_register);
> *
> * Returns 0 if ok, error value on error.
> */
> -int tracepoint_probe_unregister(struct tracepoint *tp, void *probe, void *data)
> +int tracepoint_probe_unregister(struct tracepoint *tp, void *probe, void *data,
> + gfp_t flags)
> {
> struct tracepoint_func tp_func;
> int ret;
> @@ -352,7 +352,7 @@ int tracepoint_probe_unregister(struct tracepoint *tp, void *probe, void *data)
> mutex_lock(&tracepoints_mutex);
> tp_func.func = probe;
> tp_func.data = data;
> - ret = tracepoint_remove_func(tp, &tp_func);
> + ret = tracepoint_remove_func(tp, &tp_func, flags);
> mutex_unlock(&tracepoints_mutex);
> return ret;
> }

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