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Message-ID: <aBb833yQFY5EpEFx@gondor.apana.org.au>
Date: Sun, 4 May 2025 13:36:31 +0800
From: Herbert Xu <herbert@...dor.apana.org.au>
To: David Howells <dhowells@...hat.com>
Cc: Jarkko Sakkinen <jarkko@...nel.org>, keyrings@...r.kernel.org,
Lukas Wunner <lukas@...ner.de>,
Ignat Korchagin <ignat@...udflare.com>,
"David S. Miller" <davem@...emloft.net>,
Peter Huewe <peterhuewe@....de>, Jason Gunthorpe <jgg@...pe.ca>,
Paul Moore <paul@...l-moore.com>, James Morris <jmorris@...ei.org>,
"Serge E. Hallyn" <serge@...lyn.com>,
James Bottomley <James.Bottomley@...senpartnership.com>,
Mimi Zohar <zohar@...ux.ibm.com>, linux-crypto@...r.kernel.org,
linux-kernel@...r.kernel.org, linux-integrity@...r.kernel.org,
linux-security-module@...r.kernel.org
Subject: [PATCH] KEYS: Invert FINAL_PUT bit
On Sun, May 04, 2025 at 08:35:57AM +0800, Herbert Xu wrote:
>
> Or even better, reverse the FINAL_PUT bit and call it ALIVE, so
> that you can use test_bit_acquire and clear_bit_unlock.
Something like:
---8<---
Invert the FINAL_PUT bit so that test_bit_acquire and clear_bit_unlock
can be used instead of smp_mb.
Signed-off-by: Herbert Xu <herbert@...dor.apana.org.au>
diff --git a/include/linux/key.h b/include/linux/key.h
index ba05de8579ec..aaab26d84d25 100644
--- a/include/linux/key.h
+++ b/include/linux/key.h
@@ -236,7 +236,7 @@ struct key {
#define KEY_FLAG_ROOT_CAN_INVAL 7 /* set if key can be invalidated by root without permission */
#define KEY_FLAG_KEEP 8 /* set if key should not be removed */
#define KEY_FLAG_UID_KEYRING 9 /* set if key is a user or user session keyring */
-#define KEY_FLAG_FINAL_PUT 10 /* set if final put has happened on key */
+#define KEY_FLAG_DONT_GC_YET 10 /* set if final put has not happened on key yet */
/* the key type and key description string
* - the desc is used to match a key against search criteria
diff --git a/security/keys/gc.c b/security/keys/gc.c
index f27223ea4578..d00002054ada 100644
--- a/security/keys/gc.c
+++ b/security/keys/gc.c
@@ -218,8 +218,8 @@ static void key_garbage_collector(struct work_struct *work)
key = rb_entry(cursor, struct key, serial_node);
cursor = rb_next(cursor);
- if (test_bit(KEY_FLAG_FINAL_PUT, &key->flags)) {
- smp_mb(); /* Clobber key->user after FINAL_PUT seen. */
+ if (test_bit_acquire(KEY_FLAG_DONT_GC_YET, &key->flags)) {
+ /* Clobber key->user after final put seen. */
goto found_unreferenced_key;
}
diff --git a/security/keys/key.c b/security/keys/key.c
index 7198cd2ac3a3..7be12d132c4e 100644
--- a/security/keys/key.c
+++ b/security/keys/key.c
@@ -298,6 +298,7 @@ struct key *key_alloc(struct key_type *type, const char *desc,
key->restrict_link = restrict_link;
key->last_used_at = ktime_get_real_seconds();
+ key->flags |= KEY_FLAG_DONT_GC_YET;
if (!(flags & KEY_ALLOC_NOT_IN_QUOTA))
key->flags |= 1 << KEY_FLAG_IN_QUOTA;
if (flags & KEY_ALLOC_BUILT_IN)
@@ -658,8 +659,8 @@ void key_put(struct key *key)
key->user->qnbytes -= key->quotalen;
spin_unlock_irqrestore(&key->user->lock, flags);
}
- smp_mb(); /* key->user before FINAL_PUT set. */
- set_bit(KEY_FLAG_FINAL_PUT, &key->flags);
+ /* Mark key as safe for GC after key->user done. */
+ clear_bit_unlock(KEY_FLAG_DONT_GC_YET, &key->flags);
schedule_work(&key_gc_work);
}
}
--
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
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