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

[patchbot@xxxxxxx]

commit f82b8134cbcbcca91ff325aaf4200ee55b7e2d7a
Author:     Jason Andryuk <jandryuk@xxxxxxxxx>
AuthorDate: Sun Apr 26 23:40:19 2020 -0400
Commit:     Wei Liu <wl@xxxxxxx>
CommitDate: Tue Apr 28 12:18:14 2020 +0100

    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@xxxxxxxxx>
    Reviewed-by: Samuel Thibault <samuel.thibault@xxxxxxxxxxxx>
---
 lib/sys.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/lib/sys.c b/lib/sys.c
index da434fc..c6a7b9f 100644
--- 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;
--
generated by git-patchbot for /home/xen/git/mini-os.git#master