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Wed, 07 Jan 2026 07:06:29 -0800 (PST) Date: Wed, 7 Jan 2026 15:14:03 +0000 From: Anton Protopopov To: Deepanshu Kartikey Cc: ast@kernel.org, daniel@iogearbox.net, john.fastabend@gmail.com, andrii@kernel.org, martin.lau@linux.dev, eddyz87@gmail.com, song@kernel.org, yonghong.song@linux.dev, kpsingh@kernel.org, sdf@fomichev.me, haoluo@google.com, jolsa@kernel.org, bpf@vger.kernel.org, linux-kernel@vger.kernel.org, syzbot+2c29addf92581b410079@syzkaller.appspotmail.com Subject: Re: [PATCH] bpf: Reject BPF_MAP_TYPE_INSN_ARRAY in check_reg_const_str() Message-ID: References: <20260107021037.289644-1-kartikey406@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: <20260107021037.289644-1-kartikey406@gmail.com> On 26/01/07 07:40AM, Deepanshu Kartikey wrote: > BPF_MAP_TYPE_INSN_ARRAY maps store instruction pointers in their > ips array, not string data. The map_direct_value_addr callback for > this map type returns the address of the ips array, which is not > suitable for use as a constant string argument. > > When a BPF program passes a pointer to an insn_array map value as > ARG_PTR_TO_CONST_STR (e.g., to bpf_snprintf), the verifier's > null-termination check in check_reg_const_str() operates on the > wrong memory region, and at runtime bpf_bprintf_prepare() can read > out of bounds searching for a null terminator. > > Reject BPF_MAP_TYPE_INSN_ARRAY in check_reg_const_str() since this > map type is not designed to hold string data. > > Reported-by: syzbot+2c29addf92581b410079@syzkaller.appspotmail.com > Closes: https://syzkaller.appspot.com/bug?extid=2c29addf92581b410079 > Tested-by: syzbot+2c29addf92581b410079@syzkaller.appspotmail.com > Fixes: 493d9e0d6083 ("bpf, x86: add support for indirect jumps") > Signed-off-by: Deepanshu Kartikey > --- > kernel/bpf/verifier.c | 5 +++++ > 1 file changed, 5 insertions(+) > > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c > index f0ca69f888fa..3135643d5695 100644 > --- a/kernel/bpf/verifier.c > +++ b/kernel/bpf/verifier.c > @@ -9609,6 +9609,11 @@ static int check_reg_const_str(struct bpf_verifier_env *env, > if (reg->type != PTR_TO_MAP_VALUE) > return -EINVAL; > > + if (map->map_type == BPF_MAP_TYPE_INSN_ARRAY) { > + verbose(env, "R%d points to insn_array map which cannot be used as const string\n", regno); > + return -EACCES; > + } > + > if (!bpf_map_is_rdonly(map)) { > verbose(env, "R%d does not point to a readonly map'\n", regno); > return -EACCES; > -- > 2.43.0 > Acked-by: Anton Protopopov