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certs: Fix blacklist flag type confusion

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KEY_FLAG_KEEP is not meant to be passed to keyring_alloc() or key_alloc(),
as these only take KEY_ALLOC_* flags.  KEY_FLAG_KEEP has the same value as
KEY_ALLOC_BYPASS_RESTRICTION, but fortunately only key_create_or_update()
uses it.  LSMs using the key_alloc hook don't check that flag.

KEY_FLAG_KEEP is then ignored but fortunately (again) the root user cannot
write to the blacklist keyring, so it is not possible to remove a key/hash
from it.

Fix this by adding a KEY_ALLOC_SET_KEEP flag that tells key_alloc() to set
KEY_FLAG_KEEP on the new key.  blacklist_init() can then, correctly, pass
this to keyring_alloc().

We can also use this in ima_mok_init() rather than setting the flag
manually.

Note that this doesn't fix an observable bug with the current
implementation but it is required to allow addition of new hashes to the
blacklist in the future without making it possible for them to be removed.

Fixes: 734114f878 ("KEYS: Add a system blacklist keyring")
Reported-by: Mickaël Salaün <mic@linux.microsoft.com>
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Mickaël Salaün <mic@linux.microsoft.com>
cc: Mimi Zohar <zohar@linux.vnet.ibm.com>
Cc: David Woodhouse <dwmw2@infradead.org>
This commit is contained in:
David Howells 2020-11-20 19:04:23 +01:00
parent f14602caf4
commit 4993e1f947
4 changed files with 6 additions and 4 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
certs/blacklist.c
View File

@ -162,7 +162,7 @@ static int __init blacklist_init(void)
KEY_USR_VIEW | KEY_USR_READ |
KEY_USR_SEARCH,
KEY_ALLOC_NOT_IN_QUOTA |
KEY_FLAG_KEEP,
KEY_ALLOC_SET_KEEP,
NULL, NULL);
if (IS_ERR(blacklist_keyring))
panic("Can't allocate system blacklist keyring\n");

1
include/linux/key.h
View File

@ -289,6 +289,7 @@ extern struct key *key_alloc(struct key_type *type,
#define KEY_ALLOC_BUILT_IN 0x0004 /* Key is built into kernel */
#define KEY_ALLOC_BYPASS_RESTRICTION 0x0008 /* Override the check on restricted keyrings */
#define KEY_ALLOC_UID_KEYRING 0x0010 /* allocating a user or user session keyring */
#define KEY_ALLOC_SET_KEEP 0x0020 /* Set the KEEP flag on the key/keyring */
extern void key_revoke(struct key *key);
extern void key_invalidate(struct key *key);

5
security/integrity/ima/ima_mok.c
View File

@ -38,13 +38,12 @@ __init int ima_mok_init(void)
(KEY_POS_ALL & ~KEY_POS_SETATTR) |
KEY_USR_VIEW | KEY_USR_READ |
KEY_USR_WRITE | KEY_USR_SEARCH,
KEY_ALLOC_NOT_IN_QUOTA,
KEY_ALLOC_NOT_IN_QUOTA |
KEY_ALLOC_SET_KEEP,
restriction, NULL);
if (IS_ERR(ima_blacklist_keyring))
panic("Can't allocate IMA blacklist keyring.");
set_bit(KEY_FLAG_KEEP, &ima_blacklist_keyring->flags);
return 0;
}
device_initcall(ima_mok_init);

2
security/keys/key.c
View File

@ -303,6 +303,8 @@ struct key *key_alloc(struct key_type *type, const char *desc,
key->flags |= 1 << KEY_FLAG_BUILTIN;
if (flags & KEY_ALLOC_UID_KEYRING)
key->flags |= 1 << KEY_FLAG_UID_KEYRING;
if (flags & KEY_ALLOC_SET_KEEP)
key->flags |= 1 << KEY_FLAG_KEEP;
#ifdef KEY_DEBUGGING
key->magic = KEY_DEBUG_MAGIC;