From 237bbd29f7a049d310d907f4b2716a7feef9abf3 Mon Sep 17 00:00:00 2001 From: Eric Biggers Date: Mon, 18 Sep 2017 11:37:03 -0700 Subject: KEYS: prevent creating a different user's keyrings It was possible for an unprivileged user to create the user and user session keyrings for another user. For example: sudo -u '#3000' sh -c 'keyctl add keyring _uid.4000 "" @u keyctl add keyring _uid_ses.4000 "" @u sleep 15' & sleep 1 sudo -u '#4000' keyctl describe @u sudo -u '#4000' keyctl describe @us This is problematic because these "fake" keyrings won't have the right permissions. In particular, the user who created them first will own them and will have full access to them via the possessor permissions, which can be used to compromise the security of a user's keys: -4: alswrv-----v------------ 3000 0 keyring: _uid.4000 -5: alswrv-----v------------ 3000 0 keyring: _uid_ses.4000 Fix it by marking user and user session keyrings with a flag KEY_FLAG_UID_KEYRING. Then, when searching for a user or user session keyring by name, skip all keyrings that don't have the flag set. Fixes: 69664cf16af4 ("keys: don't generate user and user session keyrings unless they're accessed") Cc: [v2.6.26+] Signed-off-by: Eric Biggers Signed-off-by: David Howells --- security/keys/key.c | 2 ++ 1 file changed, 2 insertions(+) (limited to 'security/keys/key.c') diff --git a/security/keys/key.c b/security/keys/key.c index 83da68d98b40..e5c0896c3a8f 100644 --- a/security/keys/key.c +++ b/security/keys/key.c @@ -302,6 +302,8 @@ struct key *key_alloc(struct key_type *type, const char *desc, key->flags |= 1 << KEY_FLAG_IN_QUOTA; if (flags & KEY_ALLOC_BUILT_IN) key->flags |= 1 << KEY_FLAG_BUILTIN; + if (flags & KEY_ALLOC_UID_KEYRING) + key->flags |= 1 << KEY_FLAG_UID_KEYRING; #ifdef KEY_DEBUGGING key->magic = KEY_DEBUG_MAGIC; -- cgit v1.2.3 From 8f674565d405a8c0b36ee531849df87f43e72ed5 Mon Sep 17 00:00:00 2001 From: Eric Biggers Date: Mon, 18 Sep 2017 11:37:39 -0700 Subject: KEYS: reset parent each time before searching key_user_tree In key_user_lookup(), if there is no key_user for the given uid, we drop key_user_lock, allocate a new key_user, and search the tree again. But we failed to set 'parent' to NULL at the beginning of the second search. If the tree were to be empty for the second search, the insertion would be done with an invalid 'parent', scribbling over freed memory. Fortunately this can't actually happen currently because the tree always contains at least the root_key_user. But it still should be fixed to make the code more robust. Signed-off-by: Eric Biggers Signed-off-by: David Howells --- security/keys/key.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) (limited to 'security/keys/key.c') diff --git a/security/keys/key.c b/security/keys/key.c index e5c0896c3a8f..eb914a838840 100644 --- a/security/keys/key.c +++ b/security/keys/key.c @@ -54,10 +54,10 @@ void __key_check(const struct key *key) struct key_user *key_user_lookup(kuid_t uid) { struct key_user *candidate = NULL, *user; - struct rb_node *parent = NULL; - struct rb_node **p; + struct rb_node *parent, **p; try_again: + parent = NULL; p = &key_user_tree.rb_node; spin_lock(&key_user_lock); -- cgit v1.2.3