kernel: tmpfs: Prevent read() on empty files

If we have never written to a tmpfs file, the buffer for it will have
never been allocated and that would lead to NULL pointer issues such as
system-wide crashes. Return zero bytes read if nothing was ever written.

Signed-off-by: Ian Moffett <ian@osmora.org>

1 files changed, 9 insertions, 0 deletions

diff --git a/sys/fs/tmpfs.c b/sys/fs/tmpfs.c
index 21dd7b5..6ae1c38 100644
--- a/sys/fs/tmpfs.c
+++ b/sys/fs/tmpfs.c
@@ -318,6 +318,15 @@ tmpfs_read(struct vnode *vp, struct sio_txn *sio)
         return -EIO;
     }
 
+    /*
+     * The node data is only allocated during writes, if
+     * we read this file before a write was ever done to it,
+     * np->data will be NULL. We must handle this.
+     */
+    if (np->data == NULL) {
+        return 0;
+    }
+
     /* Is this even a regular file? */
     if (np->type != VREG) {
         return -EISDIR;