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Mon, 14 Sep 2026 09:42:01 -0700 (PDT) From: Andrew Halaney Date: Mon, 14 Sep 2026 11:41:42 -0500 Subject: [PATCH 1/3] keys: add KEY_SPEC_DM_VERITY_KEYRING Precedence: bulk X-Mailing-List: linux-security-module@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20260914-ajhalaney-dmverity-key-identifier-v1-1-01922dc1366a@amutable.com> References: <20260914-ajhalaney-dmverity-key-identifier-v1-0-01922dc1366a@amutable.com> In-Reply-To: <20260914-ajhalaney-dmverity-key-identifier-v1-0-01922dc1366a@amutable.com> To: Alasdair Kergon , Mike Snitzer , Mikulas Patocka , Benjamin Marzinski , David Howells , Jarkko Sakkinen , Paul Moore , James Morris , "Serge E. Hallyn" , Eric Biggers , "Theodore Y. Ts'o" , Jonathan Corbet , Shuah Khan , Randy Dunlap Cc: dm-devel@lists.linux.dev, linux-kernel@vger.kernel.org, keyrings@vger.kernel.org, linux-security-module@vger.kernel.org, bpf@vger.kernel.org, fsverity@lists.linux.dev, linux-doc@vger.kernel.org, Andrew Halaney , "Christian Brauner (Amutable)" X-Mailer: b4 0.14.3 The .dm-verity keyring is not linked into any process keyring, so request_key() and KEYCTL_SEARCH cannot find it. Userspace has to scrape /proc/keys for the serial to use. That's not great, one could put in a bogus description containing a newline to confuse userspace further. For example, thanks to AI models, which I run as root but you could show off as any old user: # DESC=$'.dm-verity: 1\n0badf00d I--Q--- 1 perm 082f0000 0 0 keyring .dm-verity' # k=$(echo -n "1234567" | keyctl padd user "$DESC" @s) # keyctl setperm "$k" 0x3f010001 # cat /proc/keys | grep dm-verity 10402023 I------ 2 perm 082f0000 0 0 keyring .dm-verity: empty 12e0bee6 I--Q--- 1 perm 3f010001 0 0 user .dm-verity: 1 0badf00d I--Q--- 1 perm 082f0000 0 0 keyring .dm-verity: 7 0x0badf00d is not a keyring, it is the text inside our user's key description. Telling the two apart needs a KEYCTL_DESCRIBE per row which is annoying to do. i.e.: # keyctl rdescribe 0x10402023 keyring;0;0;082f0000;.dm-verity # keyctl rdescribe 0x0badf00d keyctl_describe: Required key not available Let's just give it a well known identifier, i.e.: # keyctl rdescribe -10 keyring;0;0;082f0000;.dm-verity This is exactly what commit 264d8fd2794f ("bpf, keys: Add a bpf keyring for program signature validation") did, and was the inspiration for this commit minus the spinlock bits required due to dm-verity being a module. Suggested-by: Christian Brauner (Amutable) Signed-off-by: Andrew Halaney --- drivers/md/dm-verity-verify-sig.c | 3 +++ include/linux/key.h | 1 + include/uapi/linux/keyctl.h | 1 + security/keys/process_keys.c | 33 +++++++++++++++++++++++++++++++++ 4 files changed, 38 insertions(+) diff --git a/drivers/md/dm-verity-verify-sig.c b/drivers/md/dm-verity-verify-sig.c index b2b55c41e2cb..da509dcdd7e5 100644 --- a/drivers/md/dm-verity-verify-sig.c +++ b/drivers/md/dm-verity-verify-sig.c @@ -189,11 +189,14 @@ int __init dm_verity_verify_sig_init(void) keyring_restrict(make_key_ref(dm_verity_keyring, true), NULL, NULL)) panic("dm-verity can't seal keyring\n"); + key_register_dm_verity_keyring(dm_verity_keyring); + return 0; } void dm_verity_verify_sig_exit(void) { + key_register_dm_verity_keyring(NULL); key_revoke(dm_verity_keyring); key_put(dm_verity_keyring); } diff --git a/include/linux/key.h b/include/linux/key.h index bd10fe45819d..ae8d3314fd93 100644 --- a/include/linux/key.h +++ b/include/linux/key.h @@ -441,6 +441,7 @@ extern int keyring_restrict(key_ref_t keyring, const char *type, const char *restriction); extern void key_register_bpf_keyring(struct key *keyring); +extern void key_register_dm_verity_keyring(struct key *keyring); extern struct key *key_lookup(key_serial_t id); diff --git a/include/uapi/linux/keyctl.h b/include/uapi/linux/keyctl.h index fa85b9760391..75923941f1b3 100644 --- a/include/uapi/linux/keyctl.h +++ b/include/uapi/linux/keyctl.h @@ -25,6 +25,7 @@ #define KEY_SPEC_REQKEY_AUTH_KEY -7 /* - key ID for assumed request_key auth key */ #define KEY_SPEC_REQUESTOR_KEYRING -8 /* - key ID for request_key() dest keyring */ #define KEY_SPEC_BPF_KEYRING -9 /* - key ID for the BPF-specific keyring */ +#define KEY_SPEC_DM_VERITY_KEYRING -10 /* - key ID for the .dm-verity keyring */ /* request-key default keyrings */ #define KEY_REQKEY_DEFL_NO_CHANGE -1 diff --git a/security/keys/process_keys.c b/security/keys/process_keys.c index 44358388e395..dba3df41638b 100644 --- a/security/keys/process_keys.c +++ b/security/keys/process_keys.c @@ -25,6 +25,10 @@ static DEFINE_MUTEX(key_session_mutex); /* BPF keyring reachable through KEY_SPEC_BPF_KEYRING */ static struct key *bpf_keyring __ro_after_init; +/* dm-verity keyring reachable through KEY_SPEC_DM_VERITY_KEYRING */ +static struct key *dm_verity_keyring; +static DEFINE_SPINLOCK(dm_verity_keyring_lock); + /* The root user's tracking struct */ struct key_user root_key_user = { .usage = REFCOUNT_INIT(3), @@ -607,6 +611,24 @@ void key_register_bpf_keyring(struct key *keyring) bpf_keyring = keyring; } +/** + * key_register_dm_verity_keyring - Publish the keyring for KEY_SPEC_DM_VERITY_KEYRING + * @keyring: The keyring to publish, or NULL to withdraw it + * + * Make @keyring reachable by userspace through the KEY_SPEC_DM_VERITY_KEYRING + * special key ID, so that provisioning it does not require scraping its + * serial out of /proc/keys first. dm-verity can be unloaded as a module + * and the keyring deregistered, as such serialize access with + * dm_verity_keyring_lock. + */ +void key_register_dm_verity_keyring(struct key *keyring) +{ + spin_lock(&dm_verity_keyring_lock); + dm_verity_keyring = keyring; + spin_unlock(&dm_verity_keyring_lock); +} +EXPORT_SYMBOL_GPL(key_register_dm_verity_keyring); + /* * Look up a key ID given us by userspace with a given permissions mask to get * the key it refers to. @@ -766,6 +788,17 @@ key_ref_t lookup_user_key(key_serial_t id, unsigned long lflags, key_ref = make_key_ref(key, 0); break; + case KEY_SPEC_DM_VERITY_KEYRING: + spin_lock(&dm_verity_keyring_lock); + key = dm_verity_keyring; + if (key) + __key_get(key); + spin_unlock(&dm_verity_keyring_lock); + if (!key) + goto error; + key_ref = make_key_ref(key, 0); + break; + default: key_ref = ERR_PTR(-EINVAL); if (id < 1) -- 2.55.0