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bpf: Do cleanup in bpf_bprintf_cleanup only when needed

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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: Jiri Olsa <jolsa@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20221215214430.1336195-3-jolsa@kernel.org
This commit is contained in:
Jiri Olsa 2022-12-15 22:44:29 +01:00 • committed by Daniel Borkmann
parent 78aa1cc940
commit f19a405045
3 changed files with 13 additions and 11 deletions
Download patch file Download diff file Expand all files Collapse all files

2
include/linux/bpf.h
View file

@ -2803,7 +2803,7 @@ struct bpf_bprintf_data {
int bpf_bprintf_prepare(char *fmt, u32 fmt_size, const u64 *raw_args, int bpf_bprintf_prepare(char *fmt, u32 fmt_size, const u64 *raw_args,
u32 num_args, struct bpf_bprintf_data *data); 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 */ /* the implementation of the opaque uapi struct bpf_dynptr */
struct bpf_dynptr_kern { struct bpf_dynptr_kern {

16
kernel/bpf/helpers.c
View file

@ -784,12 +784,14 @@ static int try_get_fmt_tmp_buf(char **tmp_buf)
return 0; 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)
this_cpu_dec(bpf_bprintf_nest_level); return;
preempt_enable(); if (WARN_ON_ONCE(this_cpu_read(bpf_bprintf_nest_level) == 0))
} return;
this_cpu_dec(bpf_bprintf_nest_level);
preempt_enable();
} }
/* /*
@ -1021,7 +1023,7 @@ nocopy_fmt:
err = 0; err = 0;
out: out:
if (err) if (err)
bpf_bprintf_cleanup(); bpf_bprintf_cleanup(data);
return err; 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); err = bstr_printf(str, str_size, fmt, data.bin_args);
bpf_bprintf_cleanup(); bpf_bprintf_cleanup(&data);
return err + 1; return err + 1;
} }

6
kernel/trace/bpf_trace.c
View file

@ -396,7 +396,7 @@ BPF_CALL_5(bpf_trace_printk, char *, fmt, u32, fmt_size, u64, arg1,
trace_bpf_trace_printk(buf); trace_bpf_trace_printk(buf);
raw_spin_unlock_irqrestore(&trace_printk_lock, flags); raw_spin_unlock_irqrestore(&trace_printk_lock, flags);
bpf_bprintf_cleanup(); bpf_bprintf_cleanup(&data);
return ret; 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); trace_bpf_trace_printk(buf);
raw_spin_unlock_irqrestore(&trace_printk_lock, flags); raw_spin_unlock_irqrestore(&trace_printk_lock, flags);
bpf_bprintf_cleanup(); bpf_bprintf_cleanup(&data);
return ret; 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); seq_bprintf(m, fmt, data.bin_args);
bpf_bprintf_cleanup(); bpf_bprintf_cleanup(&data);
return seq_has_overflowed(m) ? -EOVERFLOW : 0; return seq_has_overflowed(m) ? -EOVERFLOW : 0;
} }