vim-patch:9.1.2058: b_locked_split is not checked for :sbuffer

Problem:  b_locked_split is not checked for :sbuffer, which allows
          autocommands to leave windows open to freed buffers.
Solution: In do_buffer_ext, check just before possibly splitting, after
          handling 'switchbuf'. Leave win_split to handle the check for
          curbuf. (needed even if curbuf is not the target, as setting
          the buffer after splitting may fail) (Sean Dewar)

closes: vim/vim#19096

ac5c8ab6cc

Co-authored-by: Sean Dewar <6256228+seandewar@users.noreply.github.com>

src/nvim/buffer.c

@@ -1323,17 +1323,10 @@ static int do_buffer_ext(int action, int start, int dir, int count, int flags)
     return FAIL;
   }
 
-  if (action == DOBUF_GOTO && buf != curbuf) {
+  if (action == DOBUF_GOTO && buf != curbuf
-    if (!check_can_set_curbuf_forceit((flags & DOBUF_FORCEIT) != 0)) {
+      && !check_can_set_curbuf_forceit((flags & DOBUF_FORCEIT) != 0)) {
-      // disallow navigating to another buffer when 'winfixbuf' is applied
+    // disallow navigating to another buffer when 'winfixbuf' is applied
-      return FAIL;
+    return FAIL;
-    }
-    if (buf->b_locked_split) {
-      // disallow navigating to a closing buffer, which like splitting,
-      // can result in more windows displaying it
-      emsg(_(e_cannot_switch_to_a_closing_buffer));
-      return FAIL;
-    }
   }
 
   if ((action == DOBUF_GOTO || action == DOBUF_SPLIT) && (buf->b_flags & BF_DUMMY)) {
@@ -1558,15 +1551,17 @@ static int do_buffer_ext(int action, int start, int dir, int count, int flags)
   }
 
   // make "buf" the current buffer
-  if (action == DOBUF_SPLIT) {      // split window first
+  // If 'switchbuf' is set jump to the window containing "buf".
-    // If 'switchbuf' is set jump to the window containing "buf".
+  if (action == DOBUF_SPLIT && swbuf_goto_win_with_buf(buf) != NULL) {
-    if (swbuf_goto_win_with_buf(buf) != NULL) {
+    return OK;
-      return OK;
+  }
-    }
+  // Whether splitting or not, don't open a closing buffer in more windows.
-
+  if (buf != curbuf && buf->b_locked_split) {
-    if (win_split(0, 0) == FAIL) {
+    emsg(_(e_cannot_switch_to_a_closing_buffer));
-      return FAIL;
+    return FAIL;
-    }
+  }
+  if (action == DOBUF_SPLIT && win_split(0, 0) == FAIL) {  // split window first
+    return FAIL;
   }
 
   // go to current buffer - nothing to do

test/old/testdir/test_buffer.vim

@@ -591,34 +591,89 @@ endfunc
 func Test_closed_buffer_still_in_window()
   %bw!
 
+  let s:fired = 0
   let s:w = win_getid()
   new
   let s:b = bufnr()
   setl bufhidden=wipe
-
   augroup ViewClosedBuffer
     autocmd!
-    autocmd BufUnload * ++once call assert_fails(
+    autocmd BufUnload * ++once let s:fired += 1 | call assert_fails(
-          \ 'call win_execute(s:w, "' .. s:b .. 'b")', 'E1546:')
+          \ 'call win_execute(s:w, "' .. s:b .. 'buffer")', 'E1546:')
   augroup END
   quit!
   " Previously resulted in s:b being curbuf while unloaded (no memfile).
+  call assert_equal(1, s:fired)
   call assert_equal(1, bufloaded(bufnr()))
   call assert_equal(0, bufexists(s:b))
+  %bw!
+
+  new flobby
+  let s:w = win_getid()
+  let s:b = bufnr()
+  setl bufhidden=wipe
+  augroup ViewClosedBuffer
+    autocmd!
+    autocmd BufUnload * ++once let s:fired += 1
+          \| wincmd p
+          \| call assert_notequal(s:w, win_getid())
+          \| call assert_notequal(s:b, bufnr())
+          \| execute s:b 'sbuffer'
+          \| call assert_equal(s:w, win_getid())
+          \| call assert_equal(s:b, bufnr())
+  augroup END
+  " Not a problem if 'switchbuf' switches to an existing window instead.
+  set switchbuf=useopen
+  quit!
+  call assert_equal(2, s:fired)
+  call assert_equal(0, bufexists(s:b))
+  set switchbuf&
+  %bw!
+
+  edit floob
+  let s:b = bufnr()
+  enew
+  augroup ViewClosedBuffer
+    autocmd!
+    autocmd BufWipeout * ++once let s:fired += 1
+          \| call assert_fails(s:b .. 'sbuffer | wincmd p', 'E1546:')
+          \| call assert_equal(1, winnr('$')) " :sbuffer shouldn't have split.
+  augroup END
+  " Used to be a heap UAF.
+  execute s:b 'bwipeout!'
+  call assert_equal(3, s:fired)
+  call assert_equal(0, bufexists(s:b))
+  %bw!
+
+  edit flarb
+  let s:b = bufnr()
+  enew
+  let b2 = bufnr()
+  augroup ViewClosedBuffer
+    autocmd!
+    autocmd BufWipeout * ++once let s:fired += 1
+          \| call assert_fails(s:b .. 'sbuffer', 'E1159:')
+  augroup END
+  " :sbuffer still should fail if curbuf is closing, even if it's not the target
+  " buffer (as switching buffers can fail after the split)
+  bwipeout!
+  call assert_equal(4, s:fired)
+  call assert_equal(0, bufexists(b2))
+  %bw!
 
   let s:w = win_getid()
   split
   new
   let s:b = bufnr()
-
   augroup ViewClosedBuffer
     autocmd!
-    autocmd BufWipeout * ++once call win_gotoid(s:w)
+    autocmd BufWipeout * ++once let s:fired += 1 | call win_gotoid(s:w)
-          \| call assert_fails(s:b .. 'b', 'E1546:') | wincmd p
+          \| call assert_fails(s:b .. 'buffer', 'E1546:') | wincmd p
   augroup END
   bw! " Close only this buffer first; used to be a heap UAF.
+  call assert_equal(5, s:fired)
 
-  unlet! s:w s:b
+  unlet! s:w s:b s:fired
   autocmd! ViewClosedBuffer
   %bw!
 endfunc