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Miller" , Mat Martineau , linux-crypto@vger.kernel.org, linux-kernel@vger.kernel.org, Daehyeon Ko <4ncienth@gmail.com> Subject: [PATCH] KEYS: asymmetric: reject non-positive restriction keys Date: Thu, 13 Aug 2026 21:40:10 +0900 Message-ID: <20260813124010.2546648-1-4ncienth@gmail.com> X-Mailer: git-send-email 2.54.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit asymmetric_lookup_restriction() resolves the serial in a key_or_keyring restriction with key_lookup(). This can return a negative or uninstantiated key as well as a positive one, and the restriction then retains that key. When the key has the asymmetric type, key_or_keyring_common() treats it as a usable trust key and dereferences asymmetric_key_ids(trusted). Negative asymmetric keys have no payload, so linking an asymmetric key to the restricted keyring causes a NULL pointer dereference. A process can retain a negative asymmetric key after a request_key() upcall fails and use its serial to restrict a keyring it owns. Linking a valid X.509 key to that keyring then triggers the fault without special privileges. On systems configured to panic on oops, this is a local denial of service. KASAN reports: KASAN: null-ptr-deref in range [0x0000000000000010-0x0000000000000017] RIP: 0010:key_or_keyring_common+0x688/0x880 Call Trace: key_link+0x1e1/0x300 keyctl_keyring_link+0x6e/0xc0 __do_sys_keyctl+0x299/0x530 Reject keys that have not been positively instantiated before installing the restriction. The explicit NULL trust key used by key_or_keyring:0:chain remains unaffected. Fixes: 7e3c4d22083f ("KEYS: Restrict asymmetric key linkage using a specific keychain") Cc: stable@vger.kernel.org Signed-off-by: Daehyeon Ko <4ncienth@gmail.com> --- crypto/asymmetric_keys/asymmetric_type.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/crypto/asymmetric_keys/asymmetric_type.c b/crypto/asymmetric_keys/asymmetric_type.c index 16a7ae16593c9e..ce78dbc8b8c1cc 100644 --- a/crypto/asymmetric_keys/asymmetric_type.c +++ b/crypto/asymmetric_keys/asymmetric_type.c @@ -553,6 +553,11 @@ static struct key_restriction *asymmetric_lookup_restriction( ret = ERR_CAST(key); goto out; } + if (!key_is_positive(key)) { + key_put(key); + ret = ERR_PTR(-ENOKEY); + goto out; + } } ret = asymmetric_restriction_alloc(link_fn, key); base-commit: 3d6d817622b0a9721e3cc404df3469171582be13 -- 2.54.0