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Subject[PATCH] KEYS: fix keyctl_set_reqkey_keyring() to not leak thread keyrings
Date
From: Eric Biggers <ebiggers@google.com>

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,
just as we do for process keyrings.

Fixes: d84f4f992cbd ("CRED: Inaugurate COW credentials")
Cc: stable@vger.kernel.org # 2.6.29+
Signed-off-by: Eric Biggers <ebiggers@google.com>
---
security/keys/keyctl.c | 13 +++++--------
security/keys/process_keys.c | 3 +++
2 files changed, 8 insertions(+), 8 deletions(-)

diff --git a/security/keys/keyctl.c b/security/keys/keyctl.c
index 52c34532c785..6f3440530835 100644
--- a/security/keys/keyctl.c
+++ b/security/keys/keyctl.c
@@ -1253,8 +1253,8 @@ long keyctl_reject_key(key_serial_t id, unsigned timeout, unsigned 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)
{
@@ -1273,17 +1273,14 @@ long keyctl_set_reqkey_keyring(int reqkey_defl)
switch (reqkey_defl) {
case KEY_REQKEY_DEFL_THREAD_KEYRING:
ret = install_thread_keyring_to_cred(new);
- if (ret < 0)
+ if (ret < 0 && ret != -EEXIST)
goto error;
goto set;

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 && ret != -EEXIST)
+ goto error;
goto set;

case KEY_REQKEY_DEFL_DEFAULT:
diff --git a/security/keys/process_keys.c b/security/keys/process_keys.c
index b6fdd22205b1..9e5337876e52 100644
--- a/security/keys/process_keys.c
+++ b/security/keys/process_keys.c
@@ -135,6 +135,9 @@ int install_thread_keyring_to_cred(struct cred *new)
{
struct key *keyring;

+ if (new->thread_keyring)
+ return -EEXIST;
+
keyring = keyring_alloc("_tid", new->uid, new->gid, new,
KEY_POS_ALL | KEY_USR_VIEW,
KEY_ALLOC_QUOTA_OVERRUN,
--
2.12.1
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