NFSD: Prevent a potential integer overflow

If the tag length is >= U32_MAX - 3 then the "length + 4" addition
can result in an integer overflow. Address this by splitting the
decoding into several steps so that decode_cb_compound4res() does
not have to perform arithmetic on the unsafe length value.

Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Cc: stable@vger.kernel.org
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

diff --git a/fs/nfsd/nfs4callback.c b/fs/nfsd/nfs4callback.c
index b5b3ab9d719a74568829db14e47b5f2531e206e0..478b548f4147f6966aa578fca73925ee456a0cbc 100644 (file)
--- a/fs/nfsd/nfs4callback.c
+++ b/fs/nfsd/nfs4callback.c
@@ -287,17 +287,17 @@ static int decode_cb_compound4res(struct xdr_stream *xdr,
        u32 length;
        __be32 *p;
 
-       p = xdr_inline_decode(xdr, 4 + 4);
+       p = xdr_inline_decode(xdr, XDR_UNIT);
        if (unlikely(p == NULL))
                goto out_overflow;
-       hdr->status = be32_to_cpup(p++);
+       hdr->status = be32_to_cpup(p);
        /* Ignore the tag */
-       length = be32_to_cpup(p++);
-       p = xdr_inline_decode(xdr, length + 4);
-       if (unlikely(p == NULL))
+       if (xdr_stream_decode_u32(xdr, &length) < 0)
+               goto out_overflow;
+       if (xdr_inline_decode(xdr, length) == NULL)
+               goto out_overflow;
+       if (xdr_stream_decode_u32(xdr, &hdr->nops) < 0)
                goto out_overflow;
-       p += XDR_QUADLEN(length);
-       hdr->nops = be32_to_cpup(p);
        return 0;
 out_overflow:
        return -EIO;