|author||David Howells <firstname.lastname@example.org>||2017-04-18 15:31:07 +0100|
|committer||David Howells <email@example.com>||2017-04-18 15:31:35 +0100|
|parent||Linux 4.11-rc7 (diff)|
KEYS: Disallow keyrings beginning with '.' to be joined as session keyrings
This fixes CVE-2016-9604. Keyrings whose name begin with a '.' are special internal keyrings and so userspace isn't allowed to create keyrings by this name to prevent shadowing. However, the patch that added the guard didn't fix KEYCTL_JOIN_SESSION_KEYRING. Not only can that create dot-named keyrings, it can also subscribe to them as a session keyring if they grant SEARCH permission to the user. This, for example, allows a root process to set .builtin_trusted_keys as its session keyring, at which point it has full access because now the possessor permissions are added. This permits root to add extra public keys, thereby bypassing module verification. This also affects kexec and IMA. This can be tested by (as root): keyctl session .builtin_trusted_keys keyctl add user a a @s keyctl list @s which on my test box gives me: 2 keys in keyring: 180010936: ---lswrv 0 0 asymmetric: Build time autogenerated kernel key: ae3d4a31b82daa8e1a75b49dc2bba949fd992a05 801382539: --alswrv 0 0 user: a Fix this by rejecting names beginning with a '.' in the keyctl. Signed-off-by: David Howells <firstname.lastname@example.org> Acked-by: Mimi Zohar <email@example.com> cc: firstname.lastname@example.org cc: email@example.com
Diffstat (limited to 'security')
1 files changed, 7 insertions, 2 deletions
diff --git a/security/keys/keyctl.c b/security/keys/keyctl.c
index 52c34532c785..ab082a2e8fdd 100644
@@ -273,7 +273,8 @@ error:
* Create and join an anonymous session keyring or join a named session
* keyring, creating it if necessary. A named session keyring must have Search
* permission for it to be joined. Session keyrings without this permit will
- * be skipped over.
+ * be skipped over. It is not permitted for userspace to create or join
+ * keyrings whose name begin with a dot.
* If successful, the ID of the joined session keyring will be returned.
@@ -290,12 +291,16 @@ long keyctl_join_session_keyring(const char __user *_name)
ret = PTR_ERR(name);
+ ret = -EPERM;
+ if (name == '.')
+ goto error_name;
/* join the session */
ret = join_session_keyring(name);