From: Qi Tang <tpluszz77@gmail.com>
To: 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>,
Eduard Zingerman <eddyz87@gmail.com>, Song Liu <song@kernel.org>,
bpf@vger.kernel.org, Qi Tang <tpluszz77@gmail.com>
Subject: [PATCH] bpf: reject direct access to nullable PTR_TO_BUF pointers
Date: Wed, 1 Apr 2026 01:27:19 +0800 [thread overview]
Message-ID: <20260331172720.29938-1-tpluszz77@gmail.com> (raw)
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>
---
kernel/bpf/verifier.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 937c9adf1b3d..17850836943b 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -7905,7 +7905,8 @@ static int check_mem_access(struct bpf_verifier_env *env, int insn_idx, u32 regn
} else if (reg->type == CONST_PTR_TO_MAP) {
err = check_ptr_to_map_access(env, regs, regno, off, size, t,
value_regno);
- } else if (base_type(reg->type) == PTR_TO_BUF) {
+ } else if (base_type(reg->type) == PTR_TO_BUF &&
+ !type_may_be_null(reg->type)) {
bool rdonly_mem = type_is_rdonly_mem(reg->type);
u32 *max_access;
--
2.43.0
next reply other threads:[~2026-03-31 17:27 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-03-31 17:27 Qi Tang [this message]
2026-03-31 17:50 ` [PATCH] bpf: reject direct access to nullable PTR_TO_BUF pointers Eduard Zingerman
2026-04-01 2:23 ` Qi Tang
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