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sunrpc: trim off EC bytes in GSSAPI v2 unwrap

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As Bruce points out in RFC 4121, section 4.2.3:

   "In Wrap tokens that provide for confidentiality, the first 16 octets
    of the Wrap token (the "header", as defined in section 4.2.6), SHALL
    be appended to the plaintext data before encryption.  Filler octets
    MAY be inserted between the plaintext data and the "header.""

...and...

   "In Wrap tokens with confidentiality, the EC field SHALL be used to
    encode the number of octets in the filler..."

It's possible for the client to stuff different data in that area on a
retransmission, which could make the checksum come out wrong in the DRC
code.

After decrypting the blob, we should trim off any extra count bytes in
addition to the checksum blob.

Reported-by: "J. Bruce Fields" <bfields@fieldses.org>
Signed-off-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
This commit is contained in:
Jeff Layton 2013-10-10 06:55:35 -04:00 committed by J. Bruce Fields
parent 5d6baef9ab
commit cf4c024b90
1 changed files with 2 additions and 2 deletions
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4
net/sunrpc/auth_gss/gss_krb5_wrap.c
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@ -576,8 +576,8 @@ gss_unwrap_kerberos_v2(struct krb5_ctx *kctx, int offset, struct xdr_buf *buf)
buf->head[0].iov_len -= GSS_KRB5_TOK_HDR_LEN + headskip;
buf->len -= GSS_KRB5_TOK_HDR_LEN + headskip;
/* Trim off the checksum blob */
xdr_buf_trim(buf, GSS_KRB5_TOK_HDR_LEN + tailskip);
/* Trim off the trailing "extra count" and checksum blob */
xdr_buf_trim(buf, ec + GSS_KRB5_TOK_HDR_LEN + tailskip);
return GSS_S_COMPLETE;
}