Hi Ben- > On Sep 15, 2019, at 11:41 AM, Benjamin Coddington <bcodding@xxxxxxxxxx> wrote: > > The GSS Message Integrity Check data for krb5i may lie partially in the XDR > reply buffer's pages and tail. If so, we try to copy the entire MIC into > free space in the tail. But as the estimations of the slack space required > for authentication and verification have improved there may be less free > space in the tail to complete this copy -- see commit 2c94b8eca1a2 > ("SUNRPC: Use au_rslack when computing reply buffer size"). In fact, there > may only be room in the tail for a single copy of the MIC, and not part of > the MIC and then another complete copy. > > The real world failure reported is that `ls` of a directory on NFS may > sometimes return -EIO, which can be traced back to xdr_buf_read_netobj() > failing to find available free space in the tail to copy the MIC. > > Fix this by checking for the case of the MIC crossing the boundaries of > head, pages, and tail. If so, shift the buffer until the MIC is contained > completely within the pages or tail. This allows the remainder of the > function to create a sub buffer that directly address the complete MIC. > > Signed-off-by: Benjamin Coddington <bcodding@xxxxxxxxxx> > Cc: stable@xxxxxxxxxxxxxxx # v5.1 > --- > net/sunrpc/xdr.c | 32 +++++++++++++++++++------------- > 1 file changed, 19 insertions(+), 13 deletions(-) > > diff --git a/net/sunrpc/xdr.c b/net/sunrpc/xdr.c > index 48c93b9e525e..a29ce73c3029 100644 > --- a/net/sunrpc/xdr.c > +++ b/net/sunrpc/xdr.c > @@ -1237,16 +1237,29 @@ xdr_encode_word(struct xdr_buf *buf, unsigned int base, u32 obj) > EXPORT_SYMBOL_GPL(xdr_encode_word); > > /* If the netobj starting offset bytes from the start of xdr_buf is contained > - * entirely in the head or the tail, set object to point to it; otherwise > - * try to find space for it at the end of the tail, copy it there, and > - * set obj to point to it. */ > + * entirely in the head, pages, or tail, set object to point to it; otherwise > + * shift the buffer until it is contained entirely within the pages or tail. > + */ > int xdr_buf_read_netobj(struct xdr_buf *buf, struct xdr_netobj *obj, unsigned int offset) > { > struct xdr_buf subbuf; > + unsigned int boundary; > > if (xdr_decode_word(buf, offset, &obj->len)) > return -EFAULT; > - if (xdr_buf_subsegment(buf, &subbuf, offset + 4, obj->len)) > + offset += 4; > + > + /* Is the obj partially in the head? */ > + boundary = buf->head[0].iov_len; > + if (offset < boundary && (offset + obj->len) > boundary) > + xdr_shift_buf(buf, boundary - offset); > + > + /* Is the obj partially in the pages? */ > + boundary += buf->page_len; > + if (offset < boundary && (offset + obj->len) > boundary) > + xdr_shrink_pagelen(buf, boundary - offset); > + > + if (xdr_buf_subsegment(buf, &subbuf, offset, obj->len)) > return -EFAULT; > > /* Is the obj contained entirely in the head? */ > @@ -1258,17 +1271,10 @@ int xdr_buf_read_netobj(struct xdr_buf *buf, struct xdr_netobj *obj, unsigned in > if (subbuf.tail[0].iov_len == obj->len) > return 0; > > - /* use end of tail as storage for obj: > - * (We don't copy to the beginning because then we'd have > - * to worry about doing a potentially overlapping copy. > - * This assumes the object is at most half the length of the > - * tail.) */ > + /* obj is in the pages: move to end of the tail */ How about "/* Find a contiguous area in @buf to hold all of @obj */" ? > if (obj->len > buf->buflen - buf->len) > return -ENOMEM; > - if (buf->tail[0].iov_len != 0) > - obj->data = buf->tail[0].iov_base + buf->tail[0].iov_len; > - else > - obj->data = buf->head[0].iov_base + buf->head[0].iov_len; > + obj->data = buf->tail[0].iov_base + buf->tail[0].iov_len; Your new code assumes that when krb5i is in use, the upper layer will always provide a non-NULL tail->iov_len. I wouldn't swear that will always be true: The reason for the "if (buf->tail[0].iov_len)" check is to see whether the upper layer indeed has set up a tail. iov_len will be non-zero only when the upper layer has provided a tail buffer. > we can definitely keep the check, but > the second half of the statement also assumes a contiguous head/tail range. Well, it assumes that there is space in the head buffer after its end. That's not necessarily the tail. Are we sure that in the post-35e77d21baa0 world there will always be enough space after head->iov_len? A reasonable test here would be to enable SLUB poisoning and and try some complex workloads on an NFSv4 krb5i mount. > I think it's safe to just remove the test altogether and place the netobj at > the end of the tail. I'm not convinced :-) I'd like to see more justification for this claim. This is why in the long run we are better off using a scratch buffer instead of finding a spot in @buf. The rules about how the rq_rcv_buf is set up are gray; this function makes a lot of "clever" assumptions about that, and that makes this logic quite brittle. Now that we have an xdr_stream in gss_unwrap_resp_integ(), I wonder if you could use the stream's scratch xdr_buf. If not, a kmalloc should do the trick. > __read_bytes_from_xdr_buf(&subbuf, obj->data, obj->len); > return 0; > } > -- > 2.20.1 > -- Chuck Lever