[PATCH 4.9 100/128] ima: Directly assign the ima_default_policy pointer to ima_rules

Greg Kroah-Hartman
2020-06-19T16:43:31Z

From: Roberto Sassu <roberto.sassu@huawei.com>

commit 067a436b1b0aafa593344fddd711a755a58afb3b upstream.

This patch prevents the following oops:

[ 10.771813] BUG: kernel NULL pointer dereference, address: 0000000000000
[...]
[ 10.779790] RIP: 0010:ima_match_policy+0xf7/0xb80
[...]
[ 10.798576] Call Trace:
[ 10.798993] ? ima_lsm_policy_change+0x2b0/0x2b0
[ 10.799753] ? inode_init_owner+0x1a0/0x1a0
[ 10.800484] ? _raw_spin_lock+0x7a/0xd0
[ 10.801592] ima_must_appraise.part.0+0xb6/0xf0
[ 10.802313] ? ima_fix_xattr.isra.0+0xd0/0xd0
[ 10.803167] ima_must_appraise+0x4f/0x70
[ 10.804004] ima_post_path_mknod+0x2e/0x80
[ 10.804800] do_mknodat+0x396/0x3c0

It occurs when there is a failure during IMA initialization, and
ima_init_policy() is not called. IMA hooks still call ima_match_policy()
but ima_rules is NULL. This patch prevents the crash by directly assigning
the ima_default_policy pointer to ima_rules when ima_rules is defined. This
wouldn't alter the existing behavior, as ima_rules is always set at the end
of ima_init_policy().

Cc: stable@vger.kernel.org # 3.7.x
Fixes: 07f6a79415d7d ("ima: add appraise action keywords and default rules")
Reported-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
security/integrity/ima/ima_policy.c | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)

--- a/security/integrity/ima/ima_policy.c
+++ b/security/integrity/ima/ima_policy.c
@@ -150,7 +150,7 @@ static struct ima_rule_entry default_app
static LIST_HEAD(ima_default_rules);
static LIST_HEAD(ima_policy_rules);
static LIST_HEAD(ima_temp_rules);
-static struct list_head *ima_rules;
+static struct list_head *ima_rules = &ima_default_rules;

static int ima_policy __initdata;

@@ -429,7 +429,6 @@ void __init ima_init_policy(void)
temp_ima_appraise |= IMA_APPRAISE_POLICY;
}

- ima_rules = &ima_default_rules;
ima_update_policy_flag();
}