linux-kernel - Re: [PATCH 1/2] ima: check xattr value length in ima_inode

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Date:	Thu, 23 Oct 2014 18:59:07 +0300
From:	Dmitry Kasatkin <dmitry.kasatkin@...il.com>
To:	Jan Kara <jack@...e.cz>
Cc:	Dmitry Kasatkin <d.kasatkin@...sung.com>,
	Mimi Zohar <zohar@...ux.vnet.ibm.com>,
	linux-security-module <linux-security-module@...r.kernel.org>,
	linux-ima-devel <linux-ima-devel@...ts.sourceforge.net>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] ima: check xattr value length in ima_inode_setxattr()

On 23 October 2014 18:40, Jan Kara <jack@...e.cz> wrote:
> On Thu 23-10-14 16:47:17, Dmitry Kasatkin wrote:
>> ima_inode_setxattr() can be called with no value. Function does not
>> check the length so that following command can be used to produce
>> kernel oops: setfattr -n security.ima FOO. This patch fixes it.
>>
> ..
>>
>> Reported-by: Jan Kara <jack@...e.cz>
>> Signed-off-by: Dmitry Kasatkin <d.kasatkin@...sung.com>
>> ---
>>  security/integrity/ima/ima_appraise.c | 2 ++
>>  1 file changed, 2 insertions(+)
>>
>> diff --git a/security/integrity/ima/ima_appraise.c b/security/integrity/ima/ima_appraise.c
>> index 5b845af..f07aacd 100644
>> --- a/security/integrity/ima/ima_appraise.c
>> +++ b/security/integrity/ima/ima_appraise.c
>> @@ -378,6 +378,8 @@ int ima_inode_setxattr(struct dentry *dentry, const char *xattr_name,
>>       result = ima_protect_xattr(dentry, xattr_name, xattr_value,
>>                                  xattr_value_len);
>>       if (result == 1) {
>> +             if (!xattr_value_len)
>> +                     return -EINVAL;
>   Wouldn't it be safer to return EINVAL whenever xattr_value_len !=
> sizeof(evm_ima_xattr_data)?

In this function we only use first byte to identify attribute type.
sizeof(evm_ima_xattr_data) is SHA1_DIGEST_SIZE + 1.
But IMA may use any other algorithm where digest size is different.

- Dmitry


>
>                                                                 Honza
>>               ima_reset_appraise_flags(dentry->d_inode,
>>                        (xvalue->type == EVM_IMA_XATTR_DIGSIG) ? 1 : 0);
>>               result = 0;
>> --
>> 1.9.1
>>
> --
> Jan Kara <jack@...e.cz>
> SUSE Labs, CR



-- 
Thanks,
Dmitry
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