xenstore size limits

 * Documents the existing 4kby size limit on xenstore message payloads
 * Causes xs.c in libxenstore to fail locally rather than violating
   said limit (which is good because xenstored kills the client
   connection if it's exceeded).
 * Introduces some limits on path lengths in xenstored.  I trust
   no-one is using path lengths >2kby.  This is good because currently
   a domain client can create a 4kby relative path that the dom0 tools
   cannot access since they'd have to specify the somewhat longer
   absolute path.
 * Removes uses of the host's PATH_MAX (!)

Signed-off-by: Ian Jackson <ian.jackson@eu.citrix.com>

1 files changed, 5 insertions, 0 deletions

diff --git a/tools/xenstore/xs.c b/tools/xenstore/xs.c
index faa7e5c80f..a815257798 100644
--- a/tools/xenstore/xs.c
+++ b/tools/xenstore/xs.c
@@ -319,6 +319,11 @@ static void *xs_talkv(struct xs_handle *h, xs_transaction_t t,
 	for (i = 0; i < num_vecs; i++)
 		msg.len += iovec[i].iov_len;
 
+	if (msg.len > XENSTORE_PAYLOAD_MAX) {
+		errno = E2BIG;
+		return 0;
+	}
+
 	ignorepipe.sa_handler = SIG_IGN;
 	sigemptyset(&ignorepipe.sa_mask);
 	ignorepipe.sa_flags = 0;