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authorDavid Howells <dhowells@redhat.com>2012-05-11 13:56:56 +0400
committerDavid Howells <dhowells@redhat.com>2012-05-11 13:56:56 +0400
commit31d5a79d7f3d436da176a78ebc12d53c06da402e (patch)
treed39a75d7d0d0e85102ff8ce5e55e5d6ab7db7262 /include/linux/key.h
parent233e4735f2a45d9e641c2488b8d7afeb1f377dac (diff)
downloadlinux-31d5a79d7f3d436da176a78ebc12d53c06da402e.tar.xz
KEYS: Do LRU discard in full keyrings
Do an LRU discard in keyrings that are full rather than returning ENFILE. To perform this, a time_t is added to the key struct and updated by the creation of a link to a key and by a key being found as the result of a search. At the completion of a successful search, the keyrings in the path between the root of the search and the first found link to it also have their last-used times updated. Note that discarding a link to a key from a keyring does not necessarily destroy the key as there may be references held by other places. An alternate discard method that might suffice is to perform FIFO discard from the keyring, using the spare 2-byte hole in the keylist header as the index of the next link to be discarded. This is useful when using a keyring as a cache for DNS results or foreign filesystem IDs. This can be tested by the following. As root do: echo 1000 >/proc/sys/kernel/keys/root_maxkeys kr=`keyctl newring foo @s` for ((i=0; i<2000; i++)); do keyctl add user a$i a $kr; done Without this patch ENFILE should be reported when the keyring fills up. With this patch, the keyring discards keys in an LRU fashion. Note that the stored LRU time has a granularity of 1s. After doing this, /proc/key-users can be observed and should show that most of the 2000 keys have been discarded: [root@andromeda ~]# cat /proc/key-users 0: 517 516/516 513/1000 5249/20000 The "513/1000" here is the number of quota-accounted keys present for this user out of the maximum permitted. In /proc/keys, the keyring shows the number of keys it has and the number of slots it has allocated: [root@andromeda ~]# grep foo /proc/keys 200c64c4 I--Q-- 1 perm 3b3f0000 0 0 keyring foo: 509/509 The maximum is (PAGE_SIZE - header) / key pointer size. That's typically 509 on a 64-bit system and 1020 on a 32-bit system. Signed-off-by: David Howells <dhowells@redhat.com>
Diffstat (limited to 'include/linux/key.h')
-rw-r--r--include/linux/key.h1
1 files changed, 1 insertions, 0 deletions
diff --git a/include/linux/key.h b/include/linux/key.h
index c505f83c9691..13c0dcd8ee48 100644
--- a/include/linux/key.h
+++ b/include/linux/key.h
@@ -136,6 +136,7 @@ struct key {
time_t expiry; /* time at which key expires (or 0) */
time_t revoked_at; /* time at which key was revoked */
};
+ time_t last_used_at; /* last time used for LRU keyring discard */
uid_t uid;
gid_t gid;
key_perm_t perm; /* access permissions */