Linux Kernels

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. <file> 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 </file>

Linux kernel releases containing commit 6899b32

The Linux kernel releases containing this commit are as follows.

Linux kernel code changes in "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: 2020/01/11 09:46