mini-os: Avoid segfaults in tc{g,s}etattr

Commit c96c22f1d94 "mini-os: minimal implementations of some termios
functions" introduced implementations of tcgetattr and tcsetattr.
However, they do not check if files[fildes].cons.dev is non-NULL before
dereferencing.  This is not a problem for FDs allocated through
alloc_fd, but the files array pre-allocates FDs 0-2 for stdio.  Those
entries have a NULL .dev, so tc{g,s}etattr on them segfault.

ioemu-stubdom segfaults when term_init() calls tcgetattr on FD 0.

Restore tcgetattr and tcsetattr behavior when .dev is NULL equivalent to
unsupported_function as it was before c96c22f1d94.

Signed-off-by: Jason Andryuk <jandryuk@gmail.com>
Reviewed-by: Samuel Thibault <samuel.thibault@ens-lyon.org>

diff --git a/lib/sys.c b/lib/sys.c
index da434fc000a3905a9b0b6e6201480987b0d2f41e..c6a7b9f460a3b416f69d326372e07b7cf3b09f41 100644 (file)
--- a/lib/sys.c
+++ b/lib/sys.c
@@ -1472,6 +1472,11 @@ int tcsetattr(int fildes, int action, const struct termios *tios)
             return -1;
     }
 
+    if (files[fildes].cons.dev == NULL) {
+        errno = ENOSYS;
+        return -1;
+    }
+
     if (tios->c_oflag & OPOST)
         files[fildes].cons.dev->is_raw = false;
     else
@@ -1492,6 +1497,11 @@ int tcgetattr(int fildes, struct termios *tios)
         return -1;
     }
 
+    if (files[fildes].cons.dev == NULL) {
+        errno = ENOSYS;
+        return 0;
+    }
+
     if (tios == NULL) {
         errno = EINVAL;
         return -1;