Commit f19a4050 authored by Jiri Olsa's avatar Jiri Olsa Committed by Daniel Borkmann
Browse files

bpf: Do cleanup in bpf_bprintf_cleanup only when needed 



Currently we always cleanup/decrement bpf_bprintf_nest_level variable
in bpf_bprintf_cleanup if it's > 0.

There's possible scenario where this could cause a problem, when
bpf_bprintf_prepare does not get bin_args buffer (because num_args is 0)
and following bpf_bprintf_cleanup call decrements bpf_bprintf_nest_level
variable, like:

  in task context:
    bpf_bprintf_prepare(num_args != 0) increments 'bpf_bprintf_nest_level = 1'
    -> first irq :
       bpf_bprintf_prepare(num_args == 0)
       bpf_bprintf_cleanup decrements 'bpf_bprintf_nest_level = 0'
    -> second irq:
       bpf_bprintf_prepare(num_args != 0) bpf_bprintf_nest_level = 1
       gets same buffer as task context above

Adding check to bpf_bprintf_cleanup and doing the real cleanup only if we
got bin_args data in the first place.

Signed-off-by: default avatarJiri Olsa <jolsa@kernel.org>
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Acked-by: default avatarYonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20221215214430.1336195-3-jolsa@kernel.org
parent 78aa1cc9

include/linux/bpf.h

+1 −1
Original line number Diff line number Diff line
@@ -2803,7 +2803,7 @@ struct bpf_bprintf_data { 


int bpf_bprintf_prepare(char *fmt, u32 fmt_size, const u64 *raw_args,

			u32 num_args, struct bpf_bprintf_data *data);

void bpf_bprintf_cleanup(void);

void bpf_bprintf_cleanup(struct bpf_bprintf_data *data);



/* the implementation of the opaque uapi struct bpf_dynptr */

struct bpf_dynptr_kern {

kernel/bpf/helpers.c

+9 −7
Original line number Diff line number Diff line
@@ -784,13 +784,15 @@ static int try_get_fmt_tmp_buf(char **tmp_buf) 
	return 0;

}



void bpf_bprintf_cleanup(void)

void bpf_bprintf_cleanup(struct bpf_bprintf_data *data)

{

	if (this_cpu_read(bpf_bprintf_nest_level)) {

	if (!data->bin_args)

		return;

	if (WARN_ON_ONCE(this_cpu_read(bpf_bprintf_nest_level) == 0))

		return;

	this_cpu_dec(bpf_bprintf_nest_level);

	preempt_enable();

}

}



/*

 * bpf_bprintf_prepare - Generic pass on format strings for bprintf-like helpers
@@ -1021,7 +1023,7 @@ int bpf_bprintf_prepare(char *fmt, u32 fmt_size, const u64 *raw_args, 
	err = 0;

out:

	if (err)

		bpf_bprintf_cleanup();

		bpf_bprintf_cleanup(data);

	return err;

}
@@ -1047,7 +1049,7 @@ BPF_CALL_5(bpf_snprintf, char *, str, u32, str_size, char *, fmt, 


	err = bstr_printf(str, str_size, fmt, data.bin_args);



	bpf_bprintf_cleanup();

	bpf_bprintf_cleanup(&data);



	return err + 1;

}

kernel/trace/bpf_trace.c

+3 −3
Original line number Diff line number Diff line
@@ -396,7 +396,7 @@ BPF_CALL_5(bpf_trace_printk, char *, fmt, u32, fmt_size, u64, arg1, 
	trace_bpf_trace_printk(buf);

	raw_spin_unlock_irqrestore(&trace_printk_lock, flags);



	bpf_bprintf_cleanup();

	bpf_bprintf_cleanup(&data);



	return ret;

}
@@ -454,7 +454,7 @@ BPF_CALL_4(bpf_trace_vprintk, char *, fmt, u32, fmt_size, const void *, args, 
	trace_bpf_trace_printk(buf);

	raw_spin_unlock_irqrestore(&trace_printk_lock, flags);



	bpf_bprintf_cleanup();

	bpf_bprintf_cleanup(&data);



	return ret;

}
@@ -494,7 +494,7 @@ BPF_CALL_5(bpf_seq_printf, struct seq_file *, m, char *, fmt, u32, fmt_size, 


	seq_bprintf(m, fmt, data.bin_args);



	bpf_bprintf_cleanup();

	bpf_bprintf_cleanup(&data);



	return seq_has_overflowed(m) ? -EOVERFLOW : 0;

}