[PATCH 3.18 03/47] KEYS: fix keyctl_set_reqkey_keyring() to not leak thread keyrings

Greg Kroah-Hartman
2017-04-28T08:46:05Z

From: Eric Biggers <ebiggers@google.com>

commit c9f838d104fed6f2f61d68164712e3204bf5271b upstream.

This fixes CVE-2017-7472.

Running the following program as an unprivileged user exhausts kernel
memory by leaking thread keyrings:

#include <keyutils.h>

int main()
{
for (;;)
keyctl_set_reqkey_keyring(KEY_REQKEY_DEFL_THREAD_KEYRING);
}

Fix it by only creating a new thread keyring if there wasn't one before.
To make things more consistent, make install_thread_keyring_to_cred()
and install_process_keyring_to_cred() both return 0 if the corresponding
keyring is already present.

Fixes: d84f4f992cbd ("CRED: Inaugurate COW credentials")
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
security/keys/keyctl.c | 11 +++-------
security/keys/process_keys.c | 44 ++++++++++++++++++++++++++-----------------
2 files changed, 31 insertions(+), 24 deletions(-)

--- a/security/keys/keyctl.c
+++ b/security/keys/keyctl.c
@@ -1258,8 +1258,8 @@ error:
* Read or set the default keyring in which request_key() will cache keys and
* return the old setting.
*
- * If a process keyring is specified then this will be created if it doesn't
- * yet exist. The old setting will be returned if successful.
+ * If a thread or process keyring is specified then it will be created if it
+ * doesn't yet exist. The old setting will be returned if successful.
*/
long keyctl_set_reqkey_keyring(int reqkey_defl)
{
@@ -1284,11 +1284,8 @@ long keyctl_set_reqkey_keyring(int reqke

case KEY_REQKEY_DEFL_PROCESS_KEYRING:
ret = install_process_keyring_to_cred(new);
- if (ret < 0) {
- if (ret != -EEXIST)
- goto error;
- ret = 0;
- }
+ if (ret < 0)
+ goto error;
goto set;

case KEY_REQKEY_DEFL_DEFAULT:
--- a/security/keys/process_keys.c
+++ b/security/keys/process_keys.c
@@ -125,13 +125,18 @@ error:
}

/*
- * Install a fresh thread keyring directly to new credentials. This keyring is
- * allowed to overrun the quota.
+ * Install a thread keyring to the given credentials struct if it didn't have
+ * one already. This is allowed to overrun the quota.
+ *
+ * Return: 0 if a thread keyring is now present; -errno on failure.
*/
int install_thread_keyring_to_cred(struct cred *new)
{
struct key *keyring;

+ if (new->thread_keyring)
+ return 0;
+
keyring = keyring_alloc("_tid", new->uid, new->gid, new,
KEY_POS_ALL | KEY_USR_VIEW,
KEY_ALLOC_QUOTA_OVERRUN, NULL);
@@ -143,7 +148,9 @@ int install_thread_keyring_to_cred(struc
}

/*
- * Install a fresh thread keyring, discarding the old one.
+ * Install a thread keyring to the current task if it didn't have one already.
+ *
+ * Return: 0 if a thread keyring is now present; -errno on failure.
*/
static int install_thread_keyring(void)
{
@@ -154,8 +161,6 @@ static int install_thread_keyring(void)
if (!new)
return -ENOMEM;

- BUG_ON(new->thread_keyring);
-
ret = install_thread_keyring_to_cred(new);
if (ret < 0) {
abort_creds(new);
@@ -166,17 +171,17 @@ static int install_thread_keyring(void)
}

/*
- * Install a process keyring directly to a credentials struct.
+ * Install a process keyring to the given credentials struct if it didn't have
+ * one already. This is allowed to overrun the quota.
*
- * Returns -EEXIST if there was already a process keyring, 0 if one installed,
- * and other value on any other error
+ * Return: 0 if a process keyring is now present; -errno on failure.
*/
int install_process_keyring_to_cred(struct cred *new)
{
struct key *keyring;

if (new->process_keyring)
- return -EEXIST;
+ return 0;

keyring = keyring_alloc("_pid", new->uid, new->gid, new,
KEY_POS_ALL | KEY_USR_VIEW,
@@ -189,11 +194,9 @@ int install_process_keyring_to_cred(stru
}

/*
- * Make sure a process keyring is installed for the current process. The
- * existing process keyring is not replaced.
+ * Install a process keyring to the current task if it didn't have one already.
*
- * Returns 0 if there is a process keyring by the end of this function, some
- * error otherwise.
+ * Return: 0 if a process keyring is now present; -errno on failure.
*/
static int install_process_keyring(void)
{
@@ -207,14 +210,18 @@ static int install_process_keyring(void)
ret = install_process_keyring_to_cred(new);
if (ret < 0) {
abort_creds(new);
- return ret != -EEXIST ? ret : 0;
+ return ret;
}

return commit_creds(new);
}

/*
- * Install a session keyring directly to a credentials struct.
+ * Install the given keyring as the session keyring of the given credentials
+ * struct, replacing the existing one if any. If the given keyring is NULL,
+ * then install a new anonymous session keyring.
+ *
+ * Return: 0 on success; -errno on failure.
*/
int install_session_keyring_to_cred(struct cred *cred, struct key *keyring)
{
@@ -249,8 +256,11 @@ int install_session_keyring_to_cred(stru
}

/*
- * Install a session keyring, discarding the old one. If a keyring is not
- * supplied, an empty one is invented.
+ * Install the given keyring as the session keyring of the current task,
+ * replacing the existing one if any. If the given keyring is NULL, then
+ * install a new anonymous session keyring.
+ *
+ * Return: 0 on success; -errno on failure.
*/
static int install_session_keyring(struct key *keyring)
{