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KEYS: fix keyctl_set_reqkey_keyring() to not leak thread keyrings

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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: d84f4f992c ("CRED: Inaugurate COW credentials")
Cc: stable@vger.kernel.org # 2.6.29+
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: David Howells <dhowells@redhat.com>
This commit is contained in:
Eric Biggers
2017-04-18 15:31:09 +01:00
committed by David Howells
parent c1644fe041
commit c9f838d104
2 changed files with 31 additions and 24 deletions
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11
security/keys/keyctl.c
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@@ -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 reqkey_defl)
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: