linux-kernel - Re: [PATCH v12 7/11] LSM: Helpers for attribute names and filling lsm

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Message-ID: <d39d5784-058f-9298-1cdb-2f0e550b206a@schaufler-ca.com>
Date:   Fri, 30 Jun 2023 10:11:42 -0700
From:   Casey Schaufler <casey@...aufler-ca.com>
To:     Paul Moore <paul@...l-moore.com>,
        linux-security-module@...r.kernel.org
Cc:     jmorris@...ei.org, serge@...lyn.com, keescook@...omium.org,
        john.johansen@...onical.com, penguin-kernel@...ove.sakura.ne.jp,
        stephen.smalley.work@...il.com, linux-kernel@...r.kernel.org,
        linux-api@...r.kernel.org, mic@...ikod.net,
        Casey Schaufler <casey@...aufler-ca.com>
Subject: Re: [PATCH v12 7/11] LSM: Helpers for attribute names and filling
 lsm_ctx

On 6/29/2023 7:14 PM, Paul Moore wrote:
> On Jun 29, 2023 Casey Schaufler <casey@...aufler-ca.com> wrote:
>> Add lsm_name_to_attr(), which translates a text string to a
>> LSM_ATTR value if one is available.
>>
>> Add lsm_fill_user_ctx(), which fills a struct lsm_ctx, including
>> the trailing attribute value.
>>
>> All are used in module specific components of LSM system calls.
>>
>> Signed-off-by: Casey Schaufler <casey@...aufler-ca.com>
>> Reviewed-by: Serge Hallyn <serge@...lyn.com>
>> ---
>>  include/linux/security.h | 14 +++++++++++++
>>  security/lsm_syscalls.c  | 24 ++++++++++++++++++++++
>>  security/security.c      | 44 ++++++++++++++++++++++++++++++++++++++++
>>  3 files changed, 82 insertions(+)
> ..
>
>> diff --git a/security/security.c b/security/security.c
>> index 199db23581f1..72ad7197b2c9 100644
>> --- a/security/security.c
>> +++ b/security/security.c
>> @@ -770,6 +770,50 @@ static int lsm_superblock_alloc(struct super_block *sb)
>>  	return 0;
>>  }
>>  
>> +/**
>> + * lsm_fill_user_ctx - Fill a user space lsm_ctx structure
>> + * @ctx: an LSM context to be filled
>> + * @context: the new context value
>> + * @context_size: the size of the new context value
>> + * @id: LSM id
>> + * @flags: LSM defined flags
>> + *
>> + * Fill all of the fields in a user space lsm_ctx structure.
>> + * Caller is assumed to have verified that @ctx has enough space
>> + * for @context.
>> + *
>> + * The total length is padded to a multiple of 64 bits to
>> + * accomodate possible alignment issues.
> We should drop the sentence above now that alignment is the caller's
> responsibility, but since that was largely my fault I can fix this up
> during the merge assuming you're okay with that Casey.

I have to fix the error in patch 8/11 anyway. I can fix this, too.

>
>> + * Returns 0 on success, -EFAULT on a copyout error, -ENOMEM
>> + * if memory can't be allocated.
>> + */
>> +int lsm_fill_user_ctx(struct lsm_ctx __user *ctx, void *context,
>> +		      size_t context_size, u64 id, u64 flags)
>> +{
>> +	struct lsm_ctx *lctx;
>> +	size_t locallen = struct_size(lctx, ctx, context_size);
>> +	int rc = 0;
>> +
>> +	lctx = kzalloc(locallen, GFP_KERNEL);
>> +	if (lctx == NULL)
>> +		return -ENOMEM;
>> +
>> +	lctx->id = id;
>> +	lctx->flags = flags;
>> +	lctx->ctx_len = context_size;
>> +	lctx->len = locallen;
>> +
>> +	memcpy(lctx->ctx, context, context_size);
>> +
>> +	if (copy_to_user(ctx, lctx, locallen))
>> +		rc = -EFAULT;
>> +
>> +	kfree(lctx);
>> +
>> +	return rc;
>> +}
>> +
>>  /*
>>   * The default value of the LSM hook is defined in linux/lsm_hook_defs.h and
>>   * can be accessed with:
>> -- 
>> 2.40.1
> --
> paul-moore.com