commit 3bd7fa12e146c6051490d048a4acbfba974eeb04
author Christian Brabandt <cb@256bit.org> Mon Oct 02 20:59:08 2023 +0200
committer Christian Brabandt <cb@256bit.org> Mon Oct 02 20:59:47 2023 +0200
tree 16eef95edff7dd16bcf19fa40cd6d55e74e7a49c
parent 6ee7b521fa7531ef356ececc8be7575c3800f872

patch 9.0.1969: [security] buffer-overflow in trunc_string()

Problem:  buffer-overflow in trunc_string()
Solution: Add NULL at end of buffer

Currently trunc_string() assumes that when the string is too long,
buf[e-1] will always be writeable. But that assumption may not always be
true. The condition currently looks like this

    else if (e + 3 < buflen)
    [...]
    else
    {
	// can't fit in the "...", just truncate it
	buf[e - 1] = NUL;
    }

but this means, we may run into the last else clause with e still being
larger than buflen. So a buffer overflow occurs.

So instead of using `buf[e - 1]`, let's just always
truncate at `buf[buflen - 1]` which should always be writable.

Signed-off-by: Christian Brabandt <cb@256bit.org>

src/message.c

diff --git a/src/message.c b/src/message.c
index 2fc6cef..83c8b4f 100644
--- a/src/message.c
+++ b/src/message.c
@@ -353,7 +353,7 @@
     else
     {
 	// can't fit in the "...", just truncate it
-	buf[e - 1] = NUL;
+	buf[buflen - 1] = NUL;
     }
 }
 

src/testdir/test_crash.vim

diff --git a/src/testdir/test_crash.vim b/src/testdir/test_crash.vim
index a1da68e..5c83e3a 100644
--- a/src/testdir/test_crash.vim
+++ b/src/testdir/test_crash.vim
@@ -66,6 +66,12 @@
     \ '  && echo "crash 7: [OK]" >> X_crash1_result.txt' .. "\<cr>")
   call TermWait(buf, 3000)
 
+  let file = 'crash/vim_msg_trunc_poc'
+  let args = printf(cmn_args, vim, file)
+  call term_sendkeys(buf, args ..
+    \ '  || echo "crash 8: [OK]" >> X_crash1_result.txt' .. "\<cr>")
+  call TermWait(buf, 3000)
+
   " clean up
   exe buf .. "bw!"
 
@@ -79,6 +85,7 @@
       \ 'crash 5: [OK]',
       \ 'crash 6: [OK]',
       \ 'crash 7: [OK]',
+      \ 'crash 8: [OK]',
       \ ]
 
   call assert_equal(expected, getline(1, '$'))

src/version.c

diff --git a/src/version.c b/src/version.c
index 1be1462..3056f35 100644
--- a/src/version.c
+++ b/src/version.c
@@ -705,6 +705,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1969,
+/**/
     1968,
 /**/
     1967,