[PATCH] tools/xenstored: Check number of strings passed to do_control()

* [PATCH] tools/xenstored: Check number of strings passed to do_control()
@ 2017-10-27 16:32 Pawel Wieczorkiewicz
  2017-10-27 16:37 ` [PATCH for-4.10] " Ian Jackson
                   ` (2 more replies)
  0 siblings, 3 replies; 5+ messages in thread
From: Pawel Wieczorkiewicz @ 2017-10-27 16:32 UTC (permalink / raw)
  To: xen-devel
  Cc: jgross, wei.liu2, julien.grall, ian.jackson, mpohlack,
	Pawel Wieczorkiewicz, doebel

It is possible to send a zero-string message body to xenstore's
XS_CONTROL handling function. Then the number of strings is used
for an array allocation. This leads to a crash in strcmp() in a
CONTROL sub-command invocation loop.
The output of xs_count_string() should be verified and all 0 or
negative values should be rejected with an EINVAL. At least the
sub-command name must be specified.

The xenstore crash can only be triggered from within dom0 (there
is a check in do_control() rejecting all non-dom0 requests with
an EACCES).

Testing: reproduced with the following command:
python -c 'print 16*"\x00"' | nc -U $XENSTORED_RUNDIR/socket

Signed-off-by: Pawel Wieczorkiewicz <wipawel@amazon.de>
Reviewed-by: Martin Pohlack <mpohlack@amazon.de>
---
 tools/xenstore/xenstored_control.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/tools/xenstore/xenstored_control.c b/tools/xenstore/xenstored_control.c
index 7c14911..e4b8aa9 100644
--- a/tools/xenstore/xenstored_control.c
+++ b/tools/xenstore/xenstored_control.c
@@ -184,6 +184,8 @@ int do_control(struct connection *conn, struct buffered_data *in)
 		return EACCES;
 
 	num = xs_count_strings(in->buffer, in->used);
+	if (num < 1)
+		return EINVAL;
 	vec = talloc_array(in, char *, num);
 	if (!vec)
 		return ENOMEM;
-- 
1.8.3.1

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Geschaeftsfuehrer: Dr. Ralf Herbrich, Christian Schlaeger
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