Re: [PATCH RFC 09/10] SUNRPC: Remove xdr_buf_trim()

[bfields@fieldses.org (J. Bruce Fields)]

On Fri, Feb 01, 2019 at 02:58:14PM -0500, Chuck Lever wrote:
> The key action of xdr_buf_trim() is that it shortens buf->len, the
> length of the xdr_buf' content. The other actions -- shortening the
> head, pages, and tail components -- are actually not necessary. In
> some cases, changing the size of those components corrupts the RPC
> message contained in the buffer.

That's really burying the lede.... Is there an actual user-visible bug
here?

--b.

> 
> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
> ---
>  include/linux/sunrpc/xdr.h          |    1 -
>  net/sunrpc/auth_gss/gss_krb5_wrap.c |    8 ++++---
>  net/sunrpc/auth_gss/svcauth_gss.c   |    2 +-
>  net/sunrpc/xdr.c                    |   41 -----------------------------------
>  4 files changed, 6 insertions(+), 46 deletions(-)
> 
> diff --git a/include/linux/sunrpc/xdr.h b/include/linux/sunrpc/xdr.h
> index 69161cb..4ae398c 100644
> --- a/include/linux/sunrpc/xdr.h
> +++ b/include/linux/sunrpc/xdr.h
> @@ -183,7 +183,6 @@ static inline __be32 *xdr_encode_array(__be32 *p, const void *s, unsigned int le
>  extern void xdr_shift_buf(struct xdr_buf *, size_t);
>  extern void xdr_buf_from_iov(struct kvec *, struct xdr_buf *);
>  extern int xdr_buf_subsegment(struct xdr_buf *, struct xdr_buf *, unsigned int, unsigned int);
> -extern void xdr_buf_trim(struct xdr_buf *, unsigned int);
>  extern int xdr_buf_read_netobj(struct xdr_buf *, struct xdr_netobj *, unsigned int);
>  extern int read_bytes_from_xdr_buf(struct xdr_buf *, unsigned int, void *, unsigned int);
>  extern int write_bytes_to_xdr_buf(struct xdr_buf *, unsigned int, void *, unsigned int);
> diff --git a/net/sunrpc/auth_gss/gss_krb5_wrap.c b/net/sunrpc/auth_gss/gss_krb5_wrap.c
> index 5cdde6c..14a0aff 100644
> --- a/net/sunrpc/auth_gss/gss_krb5_wrap.c
> +++ b/net/sunrpc/auth_gss/gss_krb5_wrap.c
> @@ -570,14 +570,16 @@ static void rotate_left(u32 base, struct xdr_buf *buf, unsigned int shift)
>  	 */
>  	movelen = min_t(unsigned int, buf->head[0].iov_len, buf->len);
>  	movelen -= offset + GSS_KRB5_TOK_HDR_LEN + headskip;
> -	BUG_ON(offset + GSS_KRB5_TOK_HDR_LEN + headskip + movelen >
> -							buf->head[0].iov_len);
> +	if (offset + GSS_KRB5_TOK_HDR_LEN + headskip + movelen >
> +	    buf->head[0].iov_len)
> +		return GSS_S_FAILURE;
>  	memmove(ptr, ptr + GSS_KRB5_TOK_HDR_LEN + headskip, movelen);
>  	buf->head[0].iov_len -= GSS_KRB5_TOK_HDR_LEN + headskip;
>  	buf->len -= GSS_KRB5_TOK_HDR_LEN + headskip;
>  
>  	/* Trim off the trailing "extra count" and checksum blob */
> -	xdr_buf_trim(buf, ec + GSS_KRB5_TOK_HDR_LEN + tailskip);
> +	buf->len -= ec + GSS_KRB5_TOK_HDR_LEN + tailskip;
> +
>  	return GSS_S_COMPLETE;
>  }
>  
> diff --git a/net/sunrpc/auth_gss/svcauth_gss.c b/net/sunrpc/auth_gss/svcauth_gss.c
> index 152790e..f1aabab 100644
> --- a/net/sunrpc/auth_gss/svcauth_gss.c
> +++ b/net/sunrpc/auth_gss/svcauth_gss.c
> @@ -896,7 +896,7 @@ u32 svcauth_gss_flavor(struct auth_domain *dom)
>  	if (svc_getnl(&buf->head[0]) != seq)
>  		goto out;
>  	/* trim off the mic and padding at the end before returning */
> -	xdr_buf_trim(buf, round_up_to_quad(mic.len) + 4);
> +	buf->len -= 4 + round_up_to_quad(mic.len);
>  	stat = 0;
>  out:
>  	kfree(mic.data);
> diff --git a/net/sunrpc/xdr.c b/net/sunrpc/xdr.c
> index 5f0aa53..4bce619 100644
> --- a/net/sunrpc/xdr.c
> +++ b/net/sunrpc/xdr.c
> @@ -1139,47 +1139,6 @@ void xdr_enter_page(struct xdr_stream *xdr, unsigned int len)
>  }
>  EXPORT_SYMBOL_GPL(xdr_buf_subsegment);
>  
> -/**
> - * xdr_buf_trim - lop at most "len" bytes off the end of "buf"
> - * @buf: buf to be trimmed
> - * @len: number of bytes to reduce "buf" by
> - *
> - * Trim an xdr_buf by the given number of bytes by fixing up the lengths. Note
> - * that it's possible that we'll trim less than that amount if the xdr_buf is
> - * too small, or if (for instance) it's all in the head and the parser has
> - * already read too far into it.
> - */
> -void xdr_buf_trim(struct xdr_buf *buf, unsigned int len)
> -{
> -	size_t cur;
> -	unsigned int trim = len;
> -
> -	if (buf->tail[0].iov_len) {
> -		cur = min_t(size_t, buf->tail[0].iov_len, trim);
> -		buf->tail[0].iov_len -= cur;
> -		trim -= cur;
> -		if (!trim)
> -			goto fix_len;
> -	}
> -
> -	if (buf->page_len) {
> -		cur = min_t(unsigned int, buf->page_len, trim);
> -		buf->page_len -= cur;
> -		trim -= cur;
> -		if (!trim)
> -			goto fix_len;
> -	}
> -
> -	if (buf->head[0].iov_len) {
> -		cur = min_t(size_t, buf->head[0].iov_len, trim);
> -		buf->head[0].iov_len -= cur;
> -		trim -= cur;
> -	}
> -fix_len:
> -	buf->len -= (len - trim);
> -}
> -EXPORT_SYMBOL_GPL(xdr_buf_trim);
> -
>  static void __read_bytes_from_xdr_buf(struct xdr_buf *subbuf, void *obj, unsigned int len)
>  {
>  	unsigned int this_len;