linux-kernel - Re: [PATCH 1/2] ima: Directly assign the ima_default_policy pointer to ima

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Date:   Wed, 03 Jun 2020 17:30:22 -0400
From:   Mimi Zohar <zohar@...ux.ibm.com>
To:     Roberto Sassu <roberto.sassu@...wei.com>, tiwai@...e.de
Cc:     linux-integrity@...r.kernel.org,
        linux-security-module@...r.kernel.org,
        linux-kernel@...r.kernel.org, silviu.vlasceanu@...wei.com,
        stable@...r.kernel.org
Subject: Re: [PATCH 1/2] ima: Directly assign the ima_default_policy pointer
 to ima_rules

On Wed, 2020-06-03 at 17:08 +0200, Roberto Sassu wrote:
> 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@...r.kernel.org # 3.7.x
> Fixes: 07f6a79415d7d ("ima: add appraise action keywords and default rules")
> Reported-by: Takashi Iwai <tiwai@...e.de>
> Signed-off-by: Roberto Sassu <roberto.sassu@...wei.com>

Thanks, Roberto!