[Libguestfs] [nbdkit PATCH 1/5] xz: Avoid reading beyond EOF

[Eric Blake]

Check that the file is long enough before reading the header, rather
than violating assumptions of the backend that all requests have
already passed bounds checks.  Missed when converting from a plugin to
a filter.

Fixes: c879d310
Signed-off-by: Eric Blake <eblake at redhat.com>
---
 filters/xz/xzfile.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/filters/xz/xzfile.c b/filters/xz/xzfile.c
index ee4af713..1ad010ef 100644
--- a/filters/xz/xzfile.c
+++ b/filters/xz/xzfile.c
@@ -117,6 +117,10 @@ check_header_magic (struct nbdkit_next_ops *next_ops, void *nxdata)
   char buf[XZ_HEADER_MAGIC_LEN];
   int err;

+  if (next_ops->get_size (nxdata) < XZ_HEADER_MAGIC_LEN) {
+    nbdkit_error ("xz: file too short");
+    return false;
+  }
   if (next_ops->pread (nxdata, buf, XZ_HEADER_MAGIC_LEN, 0, 0, &err) == -1) {
     nbdkit_error ("xz: could not read header magic: error %d", err);
     return false;
-- 
2.21.0