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keys: safe concurrent user->{session,uid}_keyring access

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The current code can perform concurrent updates and reads on
user->session_keyring and user->uid_keyring. Add a comment to
struct user_struct to document the nontrivial locking semantics, and use
READ_ONCE() for unlocked readers and smp_store_release() for writers to
prevent memory ordering issues.

Fixes: 69664cf16a ("keys: don't generate user and user session keyrings unless they're accessed")
Signed-off-by: Jann Horn <jannh@google.com>
Signed-off-by: James Morris <james.morris@microsoft.com>
This commit is contained in:
Jann Horn
2019-03-27 16:55:08 +01:00
committed by James Morris
parent 5c7e372caa
commit 0b9dc6c9f0
3 changed files with 27 additions and 16 deletions
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5
security/keys/request_key.c
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@@ -293,11 +293,12 @@ static int construct_get_dest_keyring(struct key **_dest_keyring)
/* fall through */
case KEY_REQKEY_DEFL_USER_SESSION_KEYRING:
dest_keyring =
key_get(cred->user->session_keyring);
key_get(READ_ONCE(cred->user->session_keyring));
break;
case KEY_REQKEY_DEFL_USER_KEYRING:
dest_keyring = key_get(cred->user->uid_keyring);
dest_keyring =
key_get(READ_ONCE(cred->user->uid_keyring));
break;
case KEY_REQKEY_DEFL_GROUP_KEYRING: