linux-kernel - [34-longterm 192/209] ima: fix add LSM rule bug

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Message-Id: <1302803767-9715-79-git-send-email-paul.gortmaker@windriver.com>
Date:	Thu, 14 Apr 2011 13:55:50 -0400
From:	Paul Gortmaker <paul.gortmaker@...driver.com>
To:	stable@...nel.org, linux-kernel@...r.kernel.org
Cc:	stable-review@...nel.org, Mimi Zohar <zohar@...ux.vnet.ibm.com>,
	Mimi Zohar <zohar@...ibm.com>,
	James Morris <jmorris@...ei.org>,
	David Safford <safford@...son.ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Paul Gortmaker <paul.gortmaker@...driver.com>
Subject: [34-longterm 192/209] ima: fix add LSM rule bug

From: Mimi Zohar <zohar@...ux.vnet.ibm.com>

  =====================================================================
  | This is a commit scheduled for the next v2.6.34 longterm release. |
  | If you see a problem with using this for longterm, please comment.|
  =====================================================================

commit 867c20265459d30a01b021a9c1e81fb4c5832aa9 upstream.

If security_filter_rule_init() doesn't return a rule, then not everything
is as fine as the return code implies.

This bug only occurs when the LSM (eg. SELinux) is disabled at runtime.

Adding an empty LSM rule causes ima_match_rules() to always succeed,
ignoring any remaining rules.

 default IMA TCB policy:
  # PROC_SUPER_MAGIC
  dont_measure fsmagic=0x9fa0
  # SYSFS_MAGIC
  dont_measure fsmagic=0x62656572
  # DEBUGFS_MAGIC
  dont_measure fsmagic=0x64626720
  # TMPFS_MAGIC
  dont_measure fsmagic=0x01021994
  # SECURITYFS_MAGIC
  dont_measure fsmagic=0x73636673

  < LSM specific rule >
  dont_measure obj_type=var_log_t

  measure func=BPRM_CHECK
  measure func=FILE_MMAP mask=MAY_EXEC
  measure func=FILE_CHECK mask=MAY_READ uid=0

Thus without the patch, with the boot parameters 'tcb selinux=0', adding
the above 'dont_measure obj_type=var_log_t' rule to the default IMA TCB
measurement policy, would result in nothing being measured.  The patch
prevents the default TCB policy from being replaced.

Signed-off-by: Mimi Zohar <zohar@...ibm.com>
Cc: James Morris <jmorris@...ei.org>
Acked-by: Serge Hallyn <serge.hallyn@...onical.com>
Cc: David Safford <safford@...son.ibm.com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Paul Gortmaker <paul.gortmaker@...driver.com>
---
 security/integrity/ima/ima_policy.c |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)

diff --git a/security/integrity/ima/ima_policy.c b/security/integrity/ima/ima_policy.c
index 8643a93..14efcfe 100644
--- a/security/integrity/ima/ima_policy.c
+++ b/security/integrity/ima/ima_policy.c
@@ -250,6 +250,8 @@ static int ima_lsm_rule_init(struct ima_measure_rule_entry *entry,
 	result = security_filter_rule_init(entry->lsm[lsm_rule].type,
 					   Audit_equal, args,
 					   &entry->lsm[lsm_rule].rule);
+	if (!entry->lsm[lsm_rule].rule)
+		return -EINVAL;
 	return result;
 }
 
-- 
1.7.4.4

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