bpf: disable and restore preemption in __BPF_PROG_RUN_ARRAY

This change “bpf: disable and restore preemption in __BPF_PROG_RUN_ARRAY” (commit 6899b32) in Linux kernel is authored by Roman Gushchin <guro [at] fb.com> on Mon Apr 23 18:09:21 2018 +0100.

Description of "bpf: disable and restore preemption in __BPF_PROG_RUN_ARRAY"

The change “bpf: disable and restore preemption in __BPF_PROG_RUN_ARRAY” introduces changes as follows.

bpf: disable and restore preemption in __BPF_PROG_RUN_ARRAY

Running bpf programs requires disabled preemption,
however at least some* of the BPF_PROG_RUN_ARRAY users
do not follow this rule.

To fix this bug, and also to make it not happen in the future,
let's add explicit preemption disabling/re-enabling
to the __BPF_PROG_RUN_ARRAY code.

* for example:
 [   17.624472] RIP: 0010:__cgroup_bpf_run_filter_sk+0x1c4/0x1d0
 ...
 [   17.640890]  inet6_create+0x3eb/0x520
 [   17.641405]  __sock_create+0x242/0x340
 [   17.641939]  __sys_socket+0x57/0xe0
 [   17.642370]  ? trace_hardirqs_off_thunk+0x1a/0x1c
 [   17.642944]  SyS_socket+0xa/0x10
 [   17.643357]  do_syscall_64+0x79/0x220
 [   17.643879]  entry_SYSCALL_64_after_hwframe+0x42/0xb7

Signed-off-by: Roman Gushchin <guro@fb.com>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

Linux kernel releases containing commit 6899b32

The Linux kernel releases containing this commit are as follows.

Linux kernel code changes from "bpf: disable and restore preemption in __BPF_PROG_RUN_ARRAY"

There are 2 lines of Linux source code added/deleted in this change. Code changes to Linux kernel are as follows.

 include/linux/bpf.h | 2 ++
 1 file changed, 2 insertions(+)
 
diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 486e65e3db26..dc586cc64bc2 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -351,6 +351,7 @@ int bpf_prog_array_copy(struct bpf_prog_array __rcu *old_array,
 		struct bpf_prog **_prog, *__prog;	\
 		struct bpf_prog_array *_array;		\
 		u32 _ret = 1;				\
+		preempt_disable();			\
 		rcu_read_lock();			\
 		_array = rcu_dereference(array);	\
 		if (unlikely(check_non_null && !_array))\
@@ -362,6 +363,7 @@ int bpf_prog_array_copy(struct bpf_prog_array __rcu *old_array,
 		}					\
 _out:							\
 		rcu_read_unlock();			\
+		preempt_enable_no_resched();		\
 		_ret;					\
 	 })
 

The commit for this change in Linux stable tree is 6899b32 (patch).

Last modified: 2020/02/09