From: Eduard Zingerman <eddyz87@gmail.com>
To: Qi Tang <tpluszz77@gmail.com>,
Alexei Starovoitov <ast@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>
Cc: Andrii Nakryiko <andrii@kernel.org>,
Martin KaFai Lau <martin.lau@linux.dev>,
John Fastabend <john.fastabend@gmail.com>,
Song Liu <song@kernel.org>,
bpf@vger.kernel.org
Subject: Re: [PATCH] bpf: reject direct access to nullable PTR_TO_BUF pointers
Date: Tue, 31 Mar 2026 10:50:54 -0700 [thread overview]
Message-ID: <9594e5fdeaae8f81edd3b73ff7e263c535d74c7c.camel@gmail.com> (raw)
In-Reply-To: <20260331172720.29938-1-tpluszz77@gmail.com>
On Wed, 2026-04-01 at 01:27 +0800, Qi Tang wrote:
> check_mem_access() matches PTR_TO_BUF via base_type() which strips
> PTR_MAYBE_NULL, allowing direct dereference without a null check.
>
> Map iterator ctx->key and ctx->value are PTR_TO_BUF | PTR_MAYBE_NULL.
> On stop callbacks these are NULL, causing a kernel NULL dereference.
>
> Add a type_may_be_null() guard to the PTR_TO_BUF branch, matching the
> existing PTR_TO_BTF_ID pattern.
>
> BUG: kernel NULL pointer dereference, address: 0000000000000000
> Oops: Oops: 0000 [#1] SMP KASAN NOPTI
> RIP: 0010:bpf_prog_5f0e2be830ac3243_null_deref_iter+0x10/0x25
> Call Trace:
> bpf_iter_run_prog+0x1c2/0x2e0
> __bpf_hash_map_seq_show+0x120/0x180
> bpf_seq_read+0x29c/0x530
> vfs_read+0x179/0x930
> ksys_read+0xef/0x1c0
> do_syscall_64+0xe0/0x1290
> entry_SYSCALL_64_after_hwframe+0x76/0x7e
> Kernel panic - not syncing: Fatal exception
>
> Fixes: 20b2aff4bc15 ("bpf: Introduce MEM_RDONLY flag")
> Signed-off-by: Qi Tang <tpluszz77@gmail.com>
> ---
Hi Qi Tang,
Could you please add a selftest for this change?
[...]
next prev parent reply other threads:[~2026-03-31 17:50 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-03-31 17:27 [PATCH] bpf: reject direct access to nullable PTR_TO_BUF pointers Qi Tang
2026-03-31 17:50 ` Eduard Zingerman [this message]
2026-04-01 2:23 ` Qi Tang
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