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Thu, 02 Apr 2026 02:47:56 -0700 (PDT) From: Jiri Olsa X-Google-Original-From: Jiri Olsa Date: Thu, 2 Apr 2026 11:47:54 +0200 To: Varun R Mallya Cc: bpf@vger.kernel.org, ast@kernel.org, daniel@iogearbox.net, memxor@gmail.com, yonghong.song@linux.dev, rostedt@goodmis.org, mhiramat@kernel.org, linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org Subject: Re: [PATCH bpf v3 1/2] bpf: Reject sleepable kprobe_multi programs at attach time Message-ID: References: <20260401191126.440683-1-varunrmallya@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260401191126.440683-1-varunrmallya@gmail.com> On Thu, Apr 02, 2026 at 12:41:25AM +0530, Varun R Mallya wrote: > kprobe.multi programs run in atomic/RCU context and cannot sleep. > However, bpf_kprobe_multi_link_attach() did not validate whether the > program being attached had the sleepable flag set, allowing sleepable > helpers such as bpf_copy_from_user() to be invoked from a non-sleepable > context. > > This causes a "sleeping function called from invalid context" splat: > > BUG: sleeping function called from invalid context at ./include/linux/uaccess.h:169 > in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 1787, name: sudo > preempt_count: 1, expected: 0 > RCU nest depth: 2, expected: 0 > > Fix this by rejecting sleepable programs early in > bpf_kprobe_multi_link_attach(), before any further processing. > > Fixes: 0dcac2725406 ("bpf: Add multi kprobe link") > Signed-off-by: Varun R Mallya nice catch! Acked-by: Jiri Olsa thanks, jirka > --- > kernel/trace/bpf_trace.c | 4 ++++ > 1 file changed, 4 insertions(+) > > diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c > index 0b040a417442..af7079aa0f36 100644 > --- a/kernel/trace/bpf_trace.c > +++ b/kernel/trace/bpf_trace.c > @@ -2752,6 +2752,10 @@ int bpf_kprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *pr > if (!is_kprobe_multi(prog)) > return -EINVAL; > > + /* kprobe_multi is not allowed to be sleepable. */ > + if (prog->sleepable) > + return -EINVAL; > + > /* Writing to context is not allowed for kprobes. */ > if (prog->aux->kprobe_write_ctx) > return -EINVAL; > -- > 2.53.0 >