6.1-stable review patch. If anyone has any objections, please let me know. ------------------ From: Jiri Olsa <jolsa@xxxxxxxxxx> commit f19a4050455aad847fb93f18dc1fe502eb60f989 upstream. 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@xxxxxxxxxx> Signed-off-by: Daniel Borkmann <daniel@xxxxxxxxxxxxx> Acked-by: Yonghong Song <yhs@xxxxxx> Link: https://lore.kernel.org/bpf/20221215214430.1336195-3-jolsa@xxxxxxxxxx Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@xxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- include/linux/bpf.h | 2 +- kernel/bpf/helpers.c | 16 +++++++++------- kernel/trace/bpf_trace.c | 6 +++--- 3 files changed, 13 insertions(+), 11 deletions(-) --- a/include/linux/bpf.h +++ b/include/linux/bpf.h @@ -2747,7 +2747,7 @@ 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 { --- a/kernel/bpf/helpers.c +++ b/kernel/bpf/helpers.c @@ -781,12 +781,14 @@ static int try_get_fmt_tmp_buf(char **tm return 0; } -void bpf_bprintf_cleanup(void) +void bpf_bprintf_cleanup(struct bpf_bprintf_data *data) { - if (this_cpu_read(bpf_bprintf_nest_level)) { - this_cpu_dec(bpf_bprintf_nest_level); - preempt_enable(); - } + 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(); } /* @@ -1018,7 +1020,7 @@ nocopy_fmt: err = 0; out: if (err) - bpf_bprintf_cleanup(); + bpf_bprintf_cleanup(data); return err; } @@ -1044,7 +1046,7 @@ BPF_CALL_5(bpf_snprintf, char *, str, u3 err = bstr_printf(str, str_size, fmt, data.bin_args); - bpf_bprintf_cleanup(); + bpf_bprintf_cleanup(&data); return err + 1; } --- a/kernel/trace/bpf_trace.c +++ b/kernel/trace/bpf_trace.c @@ -395,7 +395,7 @@ BPF_CALL_5(bpf_trace_printk, char *, fmt trace_bpf_trace_printk(buf); raw_spin_unlock_irqrestore(&trace_printk_lock, flags); - bpf_bprintf_cleanup(); + bpf_bprintf_cleanup(&data); return ret; } @@ -453,7 +453,7 @@ BPF_CALL_4(bpf_trace_vprintk, char *, fm trace_bpf_trace_printk(buf); raw_spin_unlock_irqrestore(&trace_printk_lock, flags); - bpf_bprintf_cleanup(); + bpf_bprintf_cleanup(&data); return ret; } @@ -493,7 +493,7 @@ BPF_CALL_5(bpf_seq_printf, struct seq_fi seq_bprintf(m, fmt, data.bin_args); - bpf_bprintf_cleanup(); + bpf_bprintf_cleanup(&data); return seq_has_overflowed(m) ? -EOVERFLOW : 0; }