> On Feb 4, 2019, at 3:00 PM, Bruce Fields <bfields@xxxxxxxxxxxx> wrote:
>
> On Mon, Feb 04, 2019 at 02:49:11PM -0500, Chuck Lever wrote:
>>
>>
>>> On Feb 4, 2019, at 2:46 PM, bfields@xxxxxxxxxxxx wrote:
>>>
>>> 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?
>>
>> I don't think so. This is more of the form:
>>
>> a) the function does fundamentally the wrong thing, so
>>
>> b) certain changes to this code path result is unexpected and incorrect
>> behavior
>>
>> Thus typically only developers hacking on this code run into a problem.
>
> OK, got it. It'd help just to make it clear in the changelog that that
> this is an accident waiting to happen rather than a current bug (as far
> as we know).
With said improvement to the changelog, can I add your Acked-by
when I submit this through Anna's tree?
> --b.
>
>>
>>
>>> --b.
>>>
>>>>
>>>> Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
>>>> ---
>>>> 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;
>>
>> --
>> Chuck Lever
--
Chuck Lever
