6.12-stable review patch. If anyone has any objections, please let me know.
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From: David Howells dhowells@redhat.com
commit 75845c6c1a64483e9985302793dbf0dfa5f71e32 upstream.
Once a key's reference count has been reduced to 0, the garbage collector thread may destroy it at any time and so key_put() is not allowed to touch the key after that point. The most key_put() is normally allowed to do is to touch key_gc_work as that's a static global variable.
However, in an effort to speed up the reclamation of quota, this is now done in key_put() once the key's usage is reduced to 0 - but now the code is looking at the key after the deadline, which is forbidden.
Fix this by using a flag to indicate that a key can be gc'd now rather than looking at the key's refcount in the garbage collector.
Fixes: 9578e327b2b4 ("keys: update key quotas in key_put()") Reported-by: syzbot+6105ffc1ded71d194d6d@syzkaller.appspotmail.com Closes: https://lore.kernel.org/all/673b6aec.050a0220.87769.004a.GAE@google.com/ Signed-off-by: David Howells dhowells@redhat.com Tested-by: syzbot+6105ffc1ded71d194d6d@syzkaller.appspotmail.com Reviewed-by: Oleg Nesterov oleg@redhat.com Signed-off-by: Jarkko Sakkinen jarkko@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- include/linux/key.h | 1 + security/keys/gc.c | 4 +++- security/keys/key.c | 2 ++ 3 files changed, 6 insertions(+), 1 deletion(-)
--- a/include/linux/key.h +++ b/include/linux/key.h @@ -236,6 +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 */
/* the key type and key description string * - the desc is used to match a key against search criteria --- a/security/keys/gc.c +++ b/security/keys/gc.c @@ -218,8 +218,10 @@ continue_scanning: key = rb_entry(cursor, struct key, serial_node); cursor = rb_next(cursor);
- if (refcount_read(&key->usage) == 0) + if (test_bit(KEY_FLAG_FINAL_PUT, &key->flags)) { + smp_mb(); /* Clobber key->user after FINAL_PUT seen. */ goto found_unreferenced_key; + }
if (unlikely(gc_state & KEY_GC_REAPING_DEAD_1)) { if (key->type == key_gc_dead_keytype) { --- a/security/keys/key.c +++ b/security/keys/key.c @@ -658,6 +658,8 @@ 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); schedule_work(&key_gc_work); } }