From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-ej1-f41.google.com (mail-ej1-f41.google.com [209.85.218.41]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 3163242048D for ; Thu, 30 Jul 2026 12:04:41 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.218.41 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785413083; cv=none; b=Ne0wQgEH87QeXYj92DdFK+6FxEdh6qiS+wO0yim0LeVX3ZQL7Sy0zno3RzIX1Yo+vJSEGqHFf4yFEr/V5UOdDQPiHkLNF0ysw1cqpgT6e+0u7zGoOkWDVlBuDGJ53rRmG9X0qtdbQWeumUuucprEbw07jaseNT6DgGcyX3msZeM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785413083; c=relaxed/simple; bh=swNwDuiSlUIFh0rZIuggEAW2FHZ3l+1i3bs6O3kepFc=; h=From:Date:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=TITGdVTyOFaQJ7Mh9PlHM56fTwYPSLcPap745A880QUz4/hxkoQOt/YrxfTOr8/oiowta2MZe46vItLFlW7bydRkVkiwoE562e7mAOT+zaUR5auNbw609j/5plYxKIWMYm1Dm8WxsxoZfmdhFsIkbGJLlyyXZlMrSzWfDCT7zWE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com; spf=pass smtp.mailfrom=gmail.com; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b=W12xfxJe; arc=none smtp.client-ip=209.85.218.41 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="W12xfxJe" Received: by mail-ej1-f41.google.com with SMTP id a640c23a62f3a-c1600d040e4so99305866b.1 for ; Thu, 30 Jul 2026 05:04:41 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20251104; t=1785413079; x=1786017879; darn=vger.kernel.org; h=in-reply-to:content-disposition:content-type:mime-version :references:message-id:subject:cc:to:date:from:from:to:cc:subject :date:message-id:reply-to:content-type; bh=CNZCm+GVCrWjZ/ClkG+Tb1xe1AofW8D8PhoCoqHKjH8=; b=W12xfxJejuF7ysi740JJuFLrNu17H5e+OAKLbcTVuOvgzmd7LRxtYTcSHHXBQAEzzr UYGsNi5Ws7s17vwFPPhSvJNi7vpqpjlj3cTzqweT9KBMFnd43c3EoRbww24hE7rhoJNe OH1sn9BSBq1amVJTnG6D1XJwIH+lE2lTz/aTIV/LxxaL4YlOPgIxOwUFSPmvnY8Tu2T6 0Dz+XYa0BGzPb+GiqQOdCvQ9bvhNyJXOhEfbuqhpxHSla7fA87P2QEWboINL7F0a64AB 3JTp+R246NluJt1USotvHvvIGQXesNNNWcLEEtmL/OzbWCGFxzE7fjdo6esWGEArgVWi 7+ww== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1785413079; x=1786017879; h=in-reply-to:content-disposition:content-type:mime-version :references:message-id:subject:cc:to:date:from:x-gm-gg :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to :content-type; bh=CNZCm+GVCrWjZ/ClkG+Tb1xe1AofW8D8PhoCoqHKjH8=; b=YVyqGK4d5xMtBVhxaylByapIvCTo3MFfQc1Z3P/slvvkDkHVz1BAnQSMzfwHBTGks3 GrbewJnbnTav/z3X6uwNL5TW1J21ntYWEmMIyQ2qI7by4/1AChcGE5UkNVC2/8wv9/L3 RlB0J+9Ynh8lst079rT3HK76J2w3JrGuCldJG4mNsaiEVnxJukiRLe4fsluBlXNq2EkS 2XuuwHGQu6B70dV3JX9hQ2r07u9p/m5gDKdDDAyS5ByIrCElI+qRsq20lVQxYMpOq69s G3eKqenLyUZBVb7ccJ3dXeiTJYt/YotgirkD+95qT7WnkTw3GCe9DBUZ1kdzzmzmbeY0 r0wQ== X-Gm-Message-State: AOJu0YwhHjeUpBHkpMr2sInUjP1VgoDASaVyceu/SM9I3FTciUdHGnxc LWkgkaOoDuDfmm7VDG5fZnlmS8S4Lypnj7PlnqBj+/wKQtqaAEZuhCqt X-Gm-Gg: AR+sD13sv6JfQSj44M6KFgTGXTTLMQC0I9sKelgLf96wZxvNn0msL9pQRlQCW7MLLPx yKr8dSERblvCvBz2O4em/ffS0f4pWT1fcDNcwJZE2TYPVqO+LqFeSwa38toBV7prnCih9pP/AAl 4GDQd8y6CApyoN+2W2wtpPnftNqfmwvyEEL8YkOaMVJZnsh3nWcF3x8DXu6R2fT25vlrh5sWRu/ g1edQJo2ibkjtNluYvkrJzm1x2zrxEaujnSLEuPYpFZdDKLHR6NV5hVl/1pxAUUqBIwL/iJ1G/T iUpabHd96qw+ZYv5bcGhsKJk3GEtGqtv5YchyzmEgkB7duW1iuWKCBuahFNa0WUUvu/SmEB8F6d EYy5AT2OTtvAwzQbvCD35Z+X3Mqklo5GbtUpfl7zj+QnZxZEP4xtvfYhpUvmCwLwM0vVMKAr9g9 K6EKnOl1S77fGV2aeATM8qcOUrplKEH8QEhiXMLfWaTwT63GM= X-Received: by 2002:a17:906:478c:b0:c1f:ba1d:805c with SMTP id a640c23a62f3a-c1fbd30ae5fmr5937666b.19.1785413079317; Thu, 30 Jul 2026 05:04:39 -0700 (PDT) Received: from krava ([173.38.220.35]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-c1fa857800asm61245466b.16.2026.07.30.05.04.38 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 30 Jul 2026 05:04:38 -0700 (PDT) From: Jiri Olsa X-Google-Original-From: Jiri Olsa Date: Thu, 30 Jul 2026 14:04:37 +0200 To: sashiko-reviews@lists.linux.dev Cc: bpf@vger.kernel.org Subject: Re: [PATCHv2 bpf-next 06/11] bpf: Factor callchain_store function from __bpf_get_stack Message-ID: References: <20260729083807.1588544-1-jolsa@kernel.org> <20260729083807.1588544-7-jolsa@kernel.org> <20260729085751.96C341F000E9@smtp.kernel.org> Precedence: bulk X-Mailing-List: bpf@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: <20260729085751.96C341F000E9@smtp.kernel.org> On Wed, Jul 29, 2026 at 08:57:51AM +0000, sashiko-bot@kernel.org wrote: > Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider: > > Pre-existing issues: > - [Critical] Preemption can cause `trace->nr` to be modified concurrently, leading to an integer underflow in `trace_nr = trace->nr - skip` and a massive out-of-bounds `memcpy`. > -- > > --- Patch [1]: [PATCHv2 bpf-next 06/11] bpf: Factor callchain_store function from __bpf_get_stack --- > commit 41f5133836d848295ac407c006940d4f0641b50f > Author: Jiri Olsa > > bpf: Factor callchain_store function from __bpf_get_stack > > This commit factors out the callchain storage logic from __bpf_get_stack > into a new callchain_store function. The new function handles both IP and > build ID data copying. > > > diff --git a/kernel/bpf/stackmap.c b/kernel/bpf/stackmap.c > > index 41fe87d7302f2..18d1a10bf76e5 100644 > > --- a/kernel/bpf/stackmap.c > > +++ b/kernel/bpf/stackmap.c > > @@ -680,6 +680,29 @@ const struct bpf_func_proto bpf_get_stackid_proto_pe = { > > .arg3_type = ARG_ANYTHING, > > }; > > > > +static u32 callchain_store(struct perf_callchain_entry *trace, void *buf, > > + u32 elem_size, u64 flags) > > +{ > > + bool user_build_id = flags & BPF_F_USER_BUILD_ID; > > + u32 skip = flags & BPF_F_SKIP_FIELD_MASK; > > + u32 trace_nr, copy_len; > > + u64 *ips; > > + > > + trace_nr = trace->nr - skip; > > [Severity: Critical] > This is a pre-existing issue, but could this calculation underflow if > trace->nr is modified concurrently? > > Looking at __bpf_get_stack(), when called from a sleepable BPF program via > bpf_get_stack_sleepable(), it calls get_perf_callchain(). This allocates > a per-CPU recursion buffer but unpins it by calling put_callchain_entry() > before returning. > > __bpf_get_stack() then checks if trace->nr is less than skip: > > if (unlikely(!trace) || trace->nr < skip) { > if (may_fault) > rcu_read_unlock(); > goto err_fault; > } > > If the task is preempted immediately after this check (which is possible for > sleepable BPF programs under CONFIG_PREEMPT_RCU, as rcu_read_lock() does not > prevent preemption), could a new task on the same CPU trigger a BPF program > that reacquires the same level-0 recursion buffer and overwrites trace->nr > to 0? > > When the original task resumes and calls callchain_store(), it re-reads > trace->nr. If it is now 0, wouldn't 0 - skip underflow to a massive unsigned > value? > > > + copy_len = trace_nr * elem_size; > > + > > + ips = trace->ip + skip; > > + if (user_build_id) { > > + struct bpf_stack_build_id *id_offs = buf; > > + > > + for (u32 i = 0; i < trace_nr; i++) > > + id_offs[i].ip = ips[i]; > > + } else { > > + memcpy(buf, ips, copy_len); > > If the underflow occurs, would this result in a massive out-of-bounds memcpy > that could overwrite the BPF stack buffer or map value and cause memory > corruption? the preemption fix comes later in the patchset jirka