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Wed, 26 Aug 2026 22:19:01 -0700 (PDT) From: "Cen Zhang (Microsoft Security FORGE Labs)" To: ast@kernel.org, daniel@iogearbox.net, martin.lau@kernel.org Cc: ameryhung@gmail.com, davem@davemloft.net, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, horms@kernel.org, wangfushuai@baidu.com, bestswngs@gmail.com, mattbobrowski@google.com, kees@kernel.org, menglong8.dong@gmail.com, bpf@vger.kernel.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, AutonomousCodeSecurity@microsoft.com, xmei5@asu.edu, tgopinath@linux.microsoft.com, kys@microsoft.com, blbllhy@gmail.com Subject: [PATCH bpf] bpf: Fix NULL pointer dereference in __bpf_sk_storage_map_seq_show Date: Thu, 27 Aug 2026 01:18:59 -0400 Message-ID: <20260827051859.45511-1-blbllhy@gmail.com> X-Mailer: git-send-email 2.55.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Iterating a sk_storage map is two stages: bpf_sk_storage_map_seq_find_next() returns a selem, then __bpf_sk_storage_map_seq_show() uses that selem. __bpf_sk_storage_map_seq_show() re-reads selem->local_storage via rcu_dereference() with no NULL check. A concurrent close() can run bpf_selem_unlink_nofail() in between and set that field to NULL, causing a NULL dereference of sk_storage->owner. Oops: general protection fault, probably for non-canonical address 0xdffffc0000000011 net/core/bpf_sk_storage.c:809 __bpf_sk_storage_map_seq_show() bpf_seq_read+0x366/0x1120 vfs_read+0x174/0xa50 ksys_read+0xfc/0x1d0 Return if the re-read yields NULL. Fixes: 5d800f87d0a5 ("bpf: Support lockless unlink when freeing map or local storage") Reported-by: Xiang Mei (Microsoft) Cc: AutonomousCodeSecurity@microsoft.com Assisted-by: Copilot (Grok 4.6) Signed-off-by: Cen Zhang (Microsoft Security FORGE Labs) --- net/core/bpf_sk_storage.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/net/core/bpf_sk_storage.c b/net/core/bpf_sk_storage.c index 1d295a8769fa..7228520aa2b6 100644 --- a/net/core/bpf_sk_storage.c +++ b/net/core/bpf_sk_storage.c @@ -806,6 +806,8 @@ static int __bpf_sk_storage_map_seq_show(struct seq_file *seq, ctx.map = info->map; if (selem) { sk_storage = rcu_dereference(selem->local_storage); + if (!sk_storage) + return 0; ctx.sk = sk_storage->owner; ctx.value = SDATA(selem)->data; } -- 2.55.0