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ima: Directly assign the ima_default_policy pointer to ima_rules 

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: 07f6a79415 ("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>
This commit is contained in:
Roberto Sassu 2020-06-03 17:08:20 +02:00 committed by Mimi Zohar
parent 8eb613c0b8
commit 067a436b1b
1 changed files with 1 additions and 2 deletions
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3
security/integrity/ima/ima_policy.c
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@ -204,7 +204,7 @@ static struct ima_rule_entry *arch_policy_entry __ro_after_init;
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;
/* Pre-allocated buffer used for matching keyrings. */
static char *ima_keyrings;
@ -768,7 +768,6 @@ void __init ima_init_policy(void)
ARRAY_SIZE(default_appraise_rules),
IMA_DEFAULT_POLICY);
ima_rules = &ima_default_rules;
ima_update_policy_flag();
}