Subject: Re: [PATCH bpf-next v4 03/20] lsm: Refactor return value of LSM hook inode_getsecurity

From: Simon Horman <[email-masked]>
Date: Fri, 12 Jul 2024 14:31:41 +0100

On Thu, Jul 11, 2024 at 07:18:51PM +0800, Xu Kuohai wrote:
> From: Xu Kuohai <[email-masked]>
> 
> To be consistent with most LSM hooks, convert the return value of
> hook inode_getsecurity to 0 or a negative error code.
> 
> Before:
> - Hook inode_getsecurity returns size of buffer on success or a
>   negative error code on failure.
> 
> After:
> - Hook inode_getsecurity returns 0 on success or a negative error
>   code on failure. An output parameter @len is introduced to hold
>   the buffer size on success.
> 
> Signed-off-by: Xu Kuohai <[email-masked]>
> ---
>  fs/xattr.c                    | 19 ++++++++++---------
>  include/linux/lsm_hook_defs.h |  3 ++-
>  include/linux/security.h      | 12 ++++++------
>  security/commoncap.c          |  9 ++++++---
>  security/security.c           | 11 ++++++-----
>  security/selinux/hooks.c      | 16 ++++++----------
>  security/smack/smack_lsm.c    | 14 +++++++-------
>  7 files changed, 43 insertions(+), 41 deletions(-)
> 
> diff --git a/fs/xattr.c b/fs/xattr.c
> index f8b643f91a98..f4e3bedf7272 100644
> --- a/fs/xattr.c
> +++ b/fs/xattr.c
> @@ -339,27 +339,28 @@ xattr_getsecurity(struct mnt_idmap *idmap, struct inode *inode,
>  		  const char *name, void *value, size_t size)
>  {
>  	void *buffer = NULL;
> -	ssize_t len;
> +	int error;
> +	u32 len;
>  
>  	if (!value || !size) {
> -		len = security_inode_getsecurity(idmap, inode, name,
> -						 &buffer, false);
> +		error = security_inode_getsecurity(idmap, inode, name,
> +						   false, &buffer, &len);
>  		goto out_noalloc;
>  	}
>  
> -	len = security_inode_getsecurity(idmap, inode, name, &buffer,
> -					 true);
> -	if (len < 0)
> -		return len;
> +	error = security_inode_getsecurity(idmap, inode, name, true,
> +					   &buffer, &len);
> +	if (error)
> +		return error;
>  	if (size < len) {
> -		len = -ERANGE;
> +		error = -ERANGE;
>  		goto out;
>  	}
>  	memcpy(value, buffer, len);
>  out:
>  	kfree(buffer);
>  out_noalloc:
> -	return len;
> +	return error < 0 ? error : len;

Hi Xu Kuohai,

len is an unsigned 32-bit entity, but the return type of this function
is an unsigned value (ssize_t). So in theory, if len is very large,
a negative error value error will be returned.

>  }

Similarly for the handling of nattr in lsm_get_self_attr in
lsm_syscalls.c in a subsequent patch.

Flagged by Smatch.

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