From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from plesk.hostmyservers.fr (plesk.hostmyservers.fr [45.145.164.37]) (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 6437CBA33; Wed, 30 Jul 2025 07:11:01 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=45.145.164.37 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1753859463; cv=none; b=bDy8m3I8MS0VVk4AgDqWZOren1XPC3UPwf5xbzWg1pw5EA/ITz9PNx86G54X2q9NDqBT+nFyQXKe2rWi5Irk2JttYM0nclU/ym7mC5dT4REUfwHZf/krZpYadJJYAgXFCWI2/pqtzMa/Z+RumRpaqgt1oCcUVMU9jwEK6S5em28= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1753859463; c=relaxed/simple; bh=NSllsyQFECNSbwkNJwP6l/Zcq043LRtCs6+wqW9sfms=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=bmlNNh1UArCSTdsGZ4vTOoKKrKXbFo+jKQ9FRZ3SkO/HgMtHb6r/eF5wumCSJHl32tFTTdzH8cFictOildRpQNsRvDciF2cpJAj3vx6ahdCViFODpaCVgoIMeLJRD/tuEV56sciSVj/wlTKZKKh+JsQ0I3hwNQvhtELaXkWjWrI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=arnaud-lcm.com; spf=pass smtp.mailfrom=arnaud-lcm.com; arc=none smtp.client-ip=45.145.164.37 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=arnaud-lcm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arnaud-lcm.com Received: from [IPV6:2a02:8084:255b:aa00:1726:a1d9:9a49:d971] (unknown [IPv6:2a02:8084:255b:aa00:1726:a1d9:9a49:d971]) by plesk.hostmyservers.fr (Postfix) with ESMTPSA id AA64F40A9F; Wed, 30 Jul 2025 07:10:58 +0000 (UTC) Authentication-Results: Plesk; spf=pass (sender IP is 2a02:8084:255b:aa00:1726:a1d9:9a49:d971) smtp.mailfrom=contact@arnaud-lcm.com smtp.helo=[IPV6:2a02:8084:255b:aa00:1726:a1d9:9a49:d971] Received-SPF: pass (Plesk: connection is authenticated) Message-ID: <5124b615-3a71-4a44-a497-eea3b5964fda@arnaud-lcm.com> Date: Wed, 30 Jul 2025 08:10:58 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2] bpf: fix stackmap overflow check in __bpf_get_stackid() To: Yonghong Song , song@kernel.org, jolsa@kernel.org, ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org, martin.lau@linux.dev, eddyz87@gmail.com, john.fastabend@gmail.com, kpsingh@kernel.org, sdf@fomichev.me, haoluo@google.com Cc: bpf@vger.kernel.org, linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com, syzbot+c9b724fbb41cf2538b7b@syzkaller.appspotmail.com References: <20250729165622.13794-1-contact@arnaud-lcm.com> <2b69e397-a457-4dba-86f1-47b7fe87ef79@linux.dev> Content-Language: en-US From: Arnaud Lecomte In-Reply-To: <2b69e397-a457-4dba-86f1-47b7fe87ef79@linux.dev> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-PPP-Message-ID: <175385945951.4041.11384093926136790668@Plesk> X-PPP-Vhost: arnaud-lcm.com On 29/07/2025 23:45, Yonghong Song wrote: > > > On 7/29/25 9:56 AM, Arnaud Lecomte wrote: >> Syzkaller reported a KASAN slab-out-of-bounds write in >> __bpf_get_stackid() >> when copying stack trace data. The issue occurs when the perf trace >>   contains more stack entries than the stack map bucket can hold, >>   leading to an out-of-bounds write in the bucket's data array. >> For build_id mode, we use sizeof(struct bpf_stack_build_id) >>   to determine capacity, and for normal mode we use sizeof(u64). >> >> Reported-by: syzbot+c9b724fbb41cf2538b7b@syzkaller.appspotmail.com >> Closes: https://syzkaller.appspot.com/bug?extid=c9b724fbb41cf2538b7b >> Tested-by: syzbot+c9b724fbb41cf2538b7b@syzkaller.appspotmail.com >> Signed-off-by: Arnaud Lecomte > > Could you add a selftest? This way folks can easily find out what is > the problem and why this fix solves the issue correctly. > Sure, will be done after work Thanks, Arnaud >> --- >> Changes in v2: >>   - Use utilty stack_map_data_size to compute map stack map size >> --- >>   kernel/bpf/stackmap.c | 8 +++++++- >>   1 file changed, 7 insertions(+), 1 deletion(-) >> >> diff --git a/kernel/bpf/stackmap.c b/kernel/bpf/stackmap.c >> index 3615c06b7dfa..6f225d477f07 100644 >> --- a/kernel/bpf/stackmap.c >> +++ b/kernel/bpf/stackmap.c >> @@ -230,7 +230,7 @@ static long __bpf_get_stackid(struct bpf_map *map, >>       struct bpf_stack_map *smap = container_of(map, struct >> bpf_stack_map, map); >>       struct stack_map_bucket *bucket, *new_bucket, *old_bucket; >>       u32 skip = flags & BPF_F_SKIP_FIELD_MASK; >> -    u32 hash, id, trace_nr, trace_len, i; >> +    u32 hash, id, trace_nr, trace_len, i, max_depth; >>       bool user = flags & BPF_F_USER_STACK; >>       u64 *ips; >>       bool hash_matches; >> @@ -241,6 +241,12 @@ static long __bpf_get_stackid(struct bpf_map *map, >>         trace_nr = trace->nr - skip; >>       trace_len = trace_nr * sizeof(u64); >> + >> +    /* Clamp the trace to max allowed depth */ >> +    max_depth = smap->map.value_size / stack_map_data_size(map); >> +    if (trace_nr > max_depth) >> +        trace_nr = max_depth; >> + >>       ips = trace->ip + skip; >>       hash = jhash2((u32 *)ips, trace_len / sizeof(u32), 0); >>       id = hash & (smap->n_buckets - 1); > >