vim-patch:9.1.0764: [security]: use-after-free when closing a buffer (#30705)

Problem:  [security]: use-after-free when closing a buffer
Solution: When splitting the window and editing a new buffer,
          check whether the newly to be edited buffer has been marked
          for deletion and abort in this case

Github Advisory:
https://github.com/vim/vim/security/advisories/GHSA-rj48-v4mq-j4vg

https://github.com/vim/vim/commit/51b62387be93c65fa56bbabe1c3c1ea5df187641

Co-authored-by: Christian Brabandt <cb@256bit.org>

1 files changed, 10 insertions, 0 deletions

diff --git a/src/nvim/ex_cmds.c b/src/nvim/ex_cmds.c
index 4319995d87..a98de05815 100644
--- a/src/nvim/ex_cmds.c
+++ b/src/nvim/ex_cmds.c
@@ -2261,6 +2261,16 @@ int do_ecmd(int fnum, char *ffname, char *sfname, exarg_T *eap, linenr_T newlnum
     if (buf == NULL) {
       goto theend;
     }
+    // autocommands try to edit a file that is goind to be removed, abort
+    if (buf_locked(buf)) {
+      // window was split, but not editing the new buffer, reset b_nwindows again
+      if (oldwin == NULL
+          && curwin->w_buffer != NULL
+          && curwin->w_buffer->b_nwindows > 1) {
+        curwin->w_buffer->b_nwindows--;
+      }
+      goto theend;
+    }
     if (curwin->w_alt_fnum == buf->b_fnum && prev_alt_fnum != 0) {
       // reusing the buffer, keep the old alternate file
       curwin->w_alt_fnum = prev_alt_fnum;