Commit b121d1e7 authored by Alexei Starovoitov's avatar Alexei Starovoitov Committed by David S. Miller
Browse files

bpf: prevent kprobe+bpf deadlocks 



if kprobe is placed within update or delete hash map helpers
that hold bucket spin lock and triggered bpf program is trying to
grab the spinlock for the same bucket on the same cpu, it will
deadlock.
Fix it by extending existing recursion prevention mechanism.

Note, map_lookup and other tracing helpers don't have this problem,
since they don't hold any locks and don't modify global data.
bpf_trace_printk has its own recursive check and ok as well.

Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
Acked-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 8aba8b83

include/linux/bpf.h

+3 −0
Original line number Diff line number Diff line
@@ -10,6 +10,7 @@ 
#include <uapi/linux/bpf.h>

#include <linux/workqueue.h>

#include <linux/file.h>

#include <linux/percpu.h>



struct bpf_map;
@@ -163,6 +164,8 @@ bool bpf_prog_array_compatible(struct bpf_array *array, const struct bpf_prog *f 
const struct bpf_func_proto *bpf_get_trace_printk_proto(void);



#ifdef CONFIG_BPF_SYSCALL

DECLARE_PER_CPU(int, bpf_prog_active);



void bpf_register_prog_type(struct bpf_prog_type_list *tl);

void bpf_register_map_type(struct bpf_map_type_list *tl);

kernel/bpf/syscall.c

+13 −0
Original line number Diff line number Diff line
@@ -18,6 +18,8 @@ 
#include <linux/filter.h>

#include <linux/version.h>



DEFINE_PER_CPU(int, bpf_prog_active);



int sysctl_unprivileged_bpf_disabled __read_mostly;



static LIST_HEAD(bpf_map_types);
@@ -347,6 +349,11 @@ static int map_update_elem(union bpf_attr *attr) 
	if (copy_from_user(value, uvalue, value_size) != 0)

		goto free_value;



	/* must increment bpf_prog_active to avoid kprobe+bpf triggering from

	 * inside bpf map update or delete otherwise deadlocks are possible

	 */

	preempt_disable();

	__this_cpu_inc(bpf_prog_active);

	if (map->map_type == BPF_MAP_TYPE_PERCPU_HASH) {

		err = bpf_percpu_hash_update(map, key, value, attr->flags);

	} else if (map->map_type == BPF_MAP_TYPE_PERCPU_ARRAY) {
@@ -356,6 +363,8 @@ static int map_update_elem(union bpf_attr *attr) 
		err = map->ops->map_update_elem(map, key, value, attr->flags);

		rcu_read_unlock();

	}

	__this_cpu_dec(bpf_prog_active);

	preempt_enable();



free_value:

	kfree(value);
@@ -394,9 +403,13 @@ static int map_delete_elem(union bpf_attr *attr) 
	if (copy_from_user(key, ukey, map->key_size) != 0)

		goto free_key;



	preempt_disable();

	__this_cpu_inc(bpf_prog_active);

	rcu_read_lock();

	err = map->ops->map_delete_elem(map, key);

	rcu_read_unlock();

	__this_cpu_dec(bpf_prog_active);

	preempt_enable();



free_key:

	kfree(key);

kernel/trace/bpf_trace.c

+0 −2
Original line number Diff line number Diff line
@@ -13,8 +13,6 @@ 
#include <linux/ctype.h>

#include "trace.h"



static DEFINE_PER_CPU(int, bpf_prog_active);



/**

 * trace_call_bpf - invoke BPF program

 * @prog: BPF program

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