hi,
we got report of kernel crash [1][3] within bpf_event_output helper.
The reason is the nesting protection code in bpf_event_output that expects
disabled preemption, which is not guaranteed for programs executed by
bpf_prog_run_array_cg.
I managed to reproduce on tracing side where we have the same problem
in bpf_perf_event_output. The reproducer [2] just creates busy uprobe
and call bpf_perf_event_output helper a lot.
v2 changes:
- I changed 'Fixes' commits to where I saw we switched from preempt_disable
to migrate_disable, but I'm not completely sure about the patch 2, because
it was tricky to find, would be nice if somebody could check on that
thanks,
jirka
[1] https://github.com/cilium/cilium/issues/26756
[2] https://git.kernel.org/pub/scm/linux/kernel/git/jolsa/perf.git/commit/?h=bpf_output_fix_reproducer&id=8054dcc634121b884c7c331329d61d93351d03b5
[3] slack:
[66194.378161] BUG: kernel NULL pointer dereference, address: 0000000000000001
[66194.378324] #PF: supervisor instruction fetch in kernel mode
[66194.378447] #PF: error_code(0x0010) - not-present page
...
[66194.378692] Oops: 0010 [#1] PREEMPT SMP NOPTI
...
[66194.380666] <TASK>
[66194.380775] ? perf_output_sample+0x12a/0x9a0
[66194.380902] ? finish_task_switch.isra.0+0x81/0x280
[66194.381024] ? perf_event_output+0x66/0xa0
[66194.381148] ? bpf_event_output+0x13a/0x190
[66194.381270] ? bpf_event_output_data+0x22/0x40
[66194.381391] ? bpf_prog_dfc84bbde731b257_cil_sock4_connect+0x40a/0xacb
[66194.381519] ? xa_load+0x87/0xe0
[66194.381635] ? __cgroup_bpf_run_filter_sock_addr+0xc1/0x1a0
[66194.381759] ? release_sock+0x3e/0x90
[66194.381876] ? sk_setsockopt+0x1a1/0x12f0
[66194.381996] ? udp_pre_connect+0x36/0x50
[66194.382114] ? inet_dgram_connect+0x93/0xa0
[66194.382233] ? __sys_connect+0xb4/0xe0
[66194.382353] ? udp_setsockopt+0x27/0x40
[66194.382470] ? __pfx_udp_push_pending_frames+0x10/0x10
[66194.382593] ? __sys_setsockopt+0xdf/0x1a0
[66194.382713] ? __x64_sys_connect+0xf/0x20
[66194.382832] ? do_syscall_64+0x3a/0x90
[66194.382949] ? entry_SYSCALL_64_after_hwframe+0x72/0xdc
[66194.383077] </TASK>
---
Jiri Olsa (2):
bpf: Disable preemption in bpf_perf_event_output
bpf: Disable preemption in bpf_event_output
kernel/trace/bpf_trace.c | 18 ++++++++++++++----
1 file changed, 14 insertions(+), 4 deletions(-)
