[PATCH v3 3/3] keys, dns: Allow key types (eg. DNS) to be reclaimed immediately on expiry
Jeffrey E Altman
jaltman at auristor.com
Wed Dec 20 05:35:48 PST 2023
On 12/12/2023 9:46 AM, David Howells wrote:
> If a key has an expiration time, then when that time passes, the key is
> left around for a certain amount of time before being collected (5 mins by
> default) so that EKEYEXPIRED can be returned instead of ENOKEY. This is a
> problem for DNS keys because we want to redo the DNS lookup immediately at
> that point.
>
> Fix this by allowing key types to be marked such that keys of that type
> don't have this extra period, but are reclaimed as soon as they expire and
> turn this on for dns_resolver-type keys. To make this easier to handle,
> key->expiry is changed to be permanent if TIME64_MAX rather than 0.
>
> Furthermore, give such new-style negative DNS results a 10s default expiry
> if no other expiry time is set rather than allowing it to stick around
> indefinitely. This shouldn't be zero as ls will follow a failing stat call
> immediately with a second with AT_SYMLINK_NOFOLLOW added.
>
> Fixes: 1a4240f4764a ("DNS: Separate out CIFS DNS Resolver code")
> Signed-off-by: David Howells <dhowells at redhat.com>
> cc: Wang Lei <wang840925 at gmail.com>
> cc: Jeff Layton <jlayton at redhat.com>
> cc: Steve French <sfrench at us.ibm.com>
> cc: Marc Dionne <marc.dionne at auristor.com>
> cc: Jarkko Sakkinen <jarkko at kernel.org>
> cc: "David S. Miller" <davem at davemloft.net>
> cc: Eric Dumazet <edumazet at google.com>
> cc: Jakub Kicinski <kuba at kernel.org>
> cc: Paolo Abeni <pabeni at redhat.com>
> cc: linux-afs at lists.infradead.org
> cc: linux-cifs at vger.kernel.org
> cc: linux-nfs at vger.kernel.org
> cc: ceph-devel at vger.kernel.org
> cc: keyrings at vger.kernel.org
> cc: netdev at vger.kernel.org
> ---
>
> Notes:
> Changes
> =======
> ver #3)
> - Don't add to TIME64_MAX (ie. permanent) when checking expiry time.
>
> include/linux/key-type.h | 1 +
> net/dns_resolver/dns_key.c | 10 +++++++++-
> security/keys/gc.c | 31 +++++++++++++++++++++----------
> security/keys/internal.h | 11 ++++++++++-
> security/keys/key.c | 15 +++++----------
> security/keys/proc.c | 2 +-
> 6 files changed, 47 insertions(+), 23 deletions(-)
>
> diff --git a/include/linux/key-type.h b/include/linux/key-type.h
> index 7d985a1dfe4a..5caf3ce82373 100644
> --- a/include/linux/key-type.h
> +++ b/include/linux/key-type.h
> @@ -73,6 +73,7 @@ struct key_type {
>
> unsigned int flags;
> #define KEY_TYPE_NET_DOMAIN 0x00000001 /* Keys of this type have a net namespace domain */
> +#define KEY_TYPE_INSTANT_REAP 0x00000002 /* Keys of this type don't have a delay after expiring */
>
> /* vet a description */
> int (*vet_description)(const char *description);
> diff --git a/net/dns_resolver/dns_key.c b/net/dns_resolver/dns_key.c
> index 01e54b46ae0b..3233f4f25fed 100644
> --- a/net/dns_resolver/dns_key.c
> +++ b/net/dns_resolver/dns_key.c
> @@ -91,6 +91,7 @@ const struct cred *dns_resolver_cache;
> static int
> dns_resolver_preparse(struct key_preparsed_payload *prep)
> {
> + const struct dns_server_list_v1_header *v1;
> const struct dns_payload_header *bin;
> struct user_key_payload *upayload;
> unsigned long derrno;
> @@ -122,6 +123,13 @@ dns_resolver_preparse(struct key_preparsed_payload *prep)
> return -EINVAL;
> }
>
> + v1 = (const struct dns_server_list_v1_header *)bin;
> + if ((v1->status != DNS_LOOKUP_GOOD &&
> + v1->status != DNS_LOOKUP_GOOD_WITH_BAD)) {
> + if (prep->expiry == TIME64_MAX)
> + prep->expiry = ktime_get_real_seconds() + 10;
10 seconds is much longer than is needed to ensure that that the result
is available for
a second stat() from "ls" in response to a failure. I would be more
comfortable if this
were one second.
> + }
> +
> result_len = datalen;
> goto store_result;
> }
> @@ -314,7 +322,7 @@ static long dns_resolver_read(const struct key *key,
>
> struct key_type key_type_dns_resolver = {
> .name = "dns_resolver",
> - .flags = KEY_TYPE_NET_DOMAIN,
> + .flags = KEY_TYPE_NET_DOMAIN | KEY_TYPE_INSTANT_REAP,
> .preparse = dns_resolver_preparse,
> .free_preparse = dns_resolver_free_preparse,
> .instantiate = generic_key_instantiate,
> diff --git a/security/keys/gc.c b/security/keys/gc.c
> index 3c90807476eb..eaddaceda14e 100644
> --- a/security/keys/gc.c
> +++ b/security/keys/gc.c
> @@ -66,6 +66,19 @@ void key_schedule_gc(time64_t gc_at)
> }
> }
>
> +/*
> + * Set the expiration time on a key.
> + */
> +void key_set_expiry(struct key *key, time64_t expiry)
> +{
> + key->expiry = expiry;
> + if (expiry != TIME64_MAX) {
> + if (!(key->type->flags & KEY_TYPE_INSTANT_REAP))
> + expiry += key_gc_delay;
> + key_schedule_gc(expiry);
> + }
> +}
> +
> /*
> * Schedule a dead links collection run.
> */
> @@ -176,7 +189,6 @@ static void key_garbage_collector(struct work_struct *work)
> static u8 gc_state; /* Internal persistent state */
> #define KEY_GC_REAP_AGAIN 0x01 /* - Need another cycle */
> #define KEY_GC_REAPING_LINKS 0x02 /* - We need to reap links */
> -#define KEY_GC_SET_TIMER 0x04 /* - We need to restart the timer */
> #define KEY_GC_REAPING_DEAD_1 0x10 /* - We need to mark dead keys */
> #define KEY_GC_REAPING_DEAD_2 0x20 /* - We need to reap dead key links */
> #define KEY_GC_REAPING_DEAD_3 0x40 /* - We need to reap dead keys */
> @@ -184,21 +196,17 @@ static void key_garbage_collector(struct work_struct *work)
>
> struct rb_node *cursor;
> struct key *key;
> - time64_t new_timer, limit;
> + time64_t new_timer, limit, expiry;
>
> kenter("[%lx,%x]", key_gc_flags, gc_state);
>
> limit = ktime_get_real_seconds();
> - if (limit > key_gc_delay)
> - limit -= key_gc_delay;
> - else
> - limit = key_gc_delay;
>
> /* Work out what we're going to be doing in this pass */
> gc_state &= KEY_GC_REAPING_DEAD_1 | KEY_GC_REAPING_DEAD_2;
> gc_state <<= 1;
> if (test_and_clear_bit(KEY_GC_KEY_EXPIRED, &key_gc_flags))
> - gc_state |= KEY_GC_REAPING_LINKS | KEY_GC_SET_TIMER;
> + gc_state |= KEY_GC_REAPING_LINKS;
>
> if (test_and_clear_bit(KEY_GC_REAP_KEYTYPE, &key_gc_flags))
> gc_state |= KEY_GC_REAPING_DEAD_1;
> @@ -233,8 +241,11 @@ static void key_garbage_collector(struct work_struct *work)
> }
> }
>
> - if (gc_state & KEY_GC_SET_TIMER) {
> - if (key->expiry > limit && key->expiry < new_timer) {
> + expiry = key->expiry;
> + if (expiry != TIME64_MAX) {
> + if (!(key->type->flags & KEY_TYPE_INSTANT_REAP))
> + expiry += key_gc_delay;
> + if (expiry > limit && expiry < new_timer) {
> kdebug("will expire %x in %lld",
> key_serial(key), key->expiry - limit);
> new_timer = key->expiry;
> @@ -276,7 +287,7 @@ static void key_garbage_collector(struct work_struct *work)
> */
> kdebug("pass complete");
>
> - if (gc_state & KEY_GC_SET_TIMER && new_timer != (time64_t)TIME64_MAX) {
> + if (new_timer != TIME64_MAX) {
> new_timer += key_gc_delay;
> key_schedule_gc(new_timer);
> }
> diff --git a/security/keys/internal.h b/security/keys/internal.h
> index 471cf36dedc0..2cffa6dc8255 100644
> --- a/security/keys/internal.h
> +++ b/security/keys/internal.h
> @@ -167,6 +167,7 @@ extern unsigned key_gc_delay;
> extern void keyring_gc(struct key *keyring, time64_t limit);
> extern void keyring_restriction_gc(struct key *keyring,
> struct key_type *dead_type);
> +void key_set_expiry(struct key *key, time64_t expiry);
> extern void key_schedule_gc(time64_t gc_at);
> extern void key_schedule_gc_links(void);
> extern void key_gc_keytype(struct key_type *ktype);
> @@ -215,10 +216,18 @@ extern struct key *key_get_instantiation_authkey(key_serial_t target_id);
> */
> static inline bool key_is_dead(const struct key *key, time64_t limit)
> {
> + time64_t expiry = key->expiry;
> +
> + if (expiry != TIME64_MAX) {
> + if (!(key->type->flags & KEY_TYPE_INSTANT_REAP))
> + expiry += key_gc_delay;
> + if (expiry <= limit)
> + return true;
> + }
> +
> return
> key->flags & ((1 << KEY_FLAG_DEAD) |
> (1 << KEY_FLAG_INVALIDATED)) ||
> - (key->expiry > 0 && key->expiry <= limit) ||
> key->domain_tag->removed;
> }
>
> diff --git a/security/keys/key.c b/security/keys/key.c
> index 0260a1902922..5b10641debd5 100644
> --- a/security/keys/key.c
> +++ b/security/keys/key.c
> @@ -294,6 +294,7 @@ struct key *key_alloc(struct key_type *type, const char *desc,
> key->uid = uid;
> key->gid = gid;
> key->perm = perm;
> + key->expiry = TIME64_MAX;
> key->restrict_link = restrict_link;
> key->last_used_at = ktime_get_real_seconds();
>
> @@ -463,10 +464,7 @@ static int __key_instantiate_and_link(struct key *key,
> if (authkey)
> key_invalidate(authkey);
>
> - if (prep->expiry != TIME64_MAX) {
> - key->expiry = prep->expiry;
> - key_schedule_gc(prep->expiry + key_gc_delay);
> - }
> + key_set_expiry(key, prep->expiry);
> }
> }
>
> @@ -606,8 +604,7 @@ int key_reject_and_link(struct key *key,
> atomic_inc(&key->user->nikeys);
> mark_key_instantiated(key, -error);
> notify_key(key, NOTIFY_KEY_INSTANTIATED, -error);
> - key->expiry = ktime_get_real_seconds() + timeout;
> - key_schedule_gc(key->expiry + key_gc_delay);
> + key_set_expiry(key, ktime_get_real_seconds() + timeout);
>
> if (test_and_clear_bit(KEY_FLAG_USER_CONSTRUCT, &key->flags))
> awaken = 1;
> @@ -723,16 +720,14 @@ struct key_type *key_type_lookup(const char *type)
>
> void key_set_timeout(struct key *key, unsigned timeout)
> {
> - time64_t expiry = 0;
> + time64_t expiry = TIME64_MAX;
>
> /* make the changes with the locks held to prevent races */
> down_write(&key->sem);
>
> if (timeout > 0)
> expiry = ktime_get_real_seconds() + timeout;
> -
> - key->expiry = expiry;
> - key_schedule_gc(key->expiry + key_gc_delay);
> + key_set_expiry(key, expiry);
>
> up_write(&key->sem);
> }
> diff --git a/security/keys/proc.c b/security/keys/proc.c
> index d0cde6685627..4f4e2c1824f1 100644
> --- a/security/keys/proc.c
> +++ b/security/keys/proc.c
> @@ -198,7 +198,7 @@ static int proc_keys_show(struct seq_file *m, void *v)
>
> /* come up with a suitable timeout value */
> expiry = READ_ONCE(key->expiry);
> - if (expiry == 0) {
> + if (expiry == TIME64_MAX) {
> memcpy(xbuf, "perm", 5);
> } else if (now >= expiry) {
> memcpy(xbuf, "expd", 5);
>
>
Beyond the default lifetime issue the change looks good to me.
Reviewed-by: Jeffrey Altman <jaltman at auristor.com>
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