[PATCH v2] xenbus: reject unterminated directory replies

[Yousef Alhouseen <alhouseenyousef@xxxxxxxxx>]

split_strings() walks each directory entry with strlen(). Although the
transport adds a terminator after the reply buffer, a malformed reply
without a final NUL inside its advertised length would let that walk
cross the protocol payload boundary.

Reject such replies before counting the strings. Report the protocol
violation once and return -EIO to the caller.

Signed-off-by: Yousef Alhouseen <alhouseenyousef@xxxxxxxxx>
---
Changes in v2:
- Reject malformed replies instead of copying the transport-added
  terminator, as suggested by Juergen Gross.

 drivers/xen/xenbus/xenbus_xs.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/xen/xenbus/xenbus_xs.c b/drivers/xen/xenbus/xenbus_xs.c
index c202e7c55..d1cca4acb 100644
--- a/drivers/xen/xenbus/xenbus_xs.c
+++ b/drivers/xen/xenbus/xenbus_xs.c
@@ -417,6 +417,12 @@ static char **split_strings(char *strings, unsigned int 
len, unsigned int *num)
 {
        char *p, **ret;
 
+       if (len && strings[len - 1]) {
+               pr_err_once("malformed XS_DIRECTORY reply\n");
+               kfree(strings);
+               return ERR_PTR(-EIO);
+       }
+
        /* Count the strings. */
        *num = count_strings(strings, len);
 
-- 
2.54.0