[PATCH 6.1 088/127] bpf: Disable preemption in bpf_event_output

Greg Kroah-Hartman
2023-08-09T10:55:19Z

From: Jiri Olsa <jolsa@kernel.org>

commit d62cc390c2e99ae267ffe4b8d7e2e08b6c758c32 upstream.

We received report [1] of kernel crash, which is caused by
using nesting protection without disabled preemption.

The bpf_event_output can be called by programs executed by
bpf_prog_run_array_cg function that disabled migration but
keeps preemption enabled.

This can cause task to be preempted by another one inside the
nesting protection and lead eventually to two tasks using same
perf_sample_data buffer and cause crashes like:

BUG: kernel NULL pointer dereference, address: 0000000000000001
#PF: supervisor instruction fetch in kernel mode
#PF: error_code(0x0010) - not-present page
...
? perf_output_sample+0x12a/0x9a0
? finish_task_switch.isra.0+0x81/0x280
? perf_event_output+0x66/0xa0
? bpf_event_output+0x13a/0x190
? bpf_event_output_data+0x22/0x40
? bpf_prog_dfc84bbde731b257_cil_sock4_connect+0x40a/0xacb
? xa_load+0x87/0xe0
? __cgroup_bpf_run_filter_sock_addr+0xc1/0x1a0
? release_sock+0x3e/0x90
? sk_setsockopt+0x1a1/0x12f0
? udp_pre_connect+0x36/0x50
? inet_dgram_connect+0x93/0xa0
? __sys_connect+0xb4/0xe0
? udp_setsockopt+0x27/0x40
? __pfx_udp_push_pending_frames+0x10/0x10
? __sys_setsockopt+0xdf/0x1a0
? __x64_sys_connect+0xf/0x20
? do_syscall_64+0x3a/0x90
? entry_SYSCALL_64_after_hwframe+0x72/0xdc

Fixing this by disabling preemption in bpf_event_output.

[1] https://github.com/cilium/cilium/issues/26756
Cc: stable@vger.kernel.org
Reported-by: Oleg "livelace" Popov <o.popov@livelace.ru>
Closes: https://github.com/cilium/cilium/issues/26756
Fixes: 2a916f2f546c ("bpf: Use migrate_disable/enable in array macros and cgroup/lirc code.")
Acked-by: Hou Tao <houtao1@huawei.com>
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Link: https://lore.kernel.org/r/20230725084206.580930-3-jolsa@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
kernel/trace/bpf_trace.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)

--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -720,7 +720,6 @@ static DEFINE_PER_CPU(struct bpf_trace_s
u64 bpf_event_output(struct bpf_map *map, u64 flags, void *meta, u64 meta_size,
void *ctx, u64 ctx_size, bpf_ctx_copy_t ctx_copy)
{
- int nest_level = this_cpu_inc_return(bpf_event_output_nest_level);
struct perf_raw_frag frag = {
.copy = ctx_copy,
.size = ctx_size,
@@ -737,8 +736,12 @@ u64 bpf_event_output(struct bpf_map *map
};
struct perf_sample_data *sd;
struct pt_regs *regs;
+ int nest_level;
u64 ret;

+ preempt_disable();
+ nest_level = this_cpu_inc_return(bpf_event_output_nest_level);
+
if (WARN_ON_ONCE(nest_level > ARRAY_SIZE(bpf_misc_sds.sds))) {
ret = -EBUSY;
goto out;
@@ -754,6 +757,7 @@ u64 bpf_event_output(struct bpf_map *map
ret = __bpf_perf_event_output(regs, map, flags, sd);
out:
this_cpu_dec(bpf_event_output_nest_level);
+ preempt_enable();
return ret;
}