patch 9.2.0436: Buffer overflow when parsing overlong errorformat lines

Problem:  When an error line in a file passed to :cfile / :cgetfile is
          longer than IOSIZE, qf_parse_file_pfx() copies the tail
          into the fixed-size IObuff with STRMOVE(), overflowing the heap buffer.
          The same code path can also loop indefinitely because
          qf_parse_file_pfx() always returns QF_MULTISCAN when a
          tail is present, and qf_init_ext() unconditionally goes
          to "restofline" without bounding the tail length (Nabih).
Solution: Remove the STRMOVE() into IObuff.  In the QF_MULTISCAN
          branch, alias linebuf into the tail directly and update
          linelen, requiring strict progress (new length less than
          the previous length) before retrying; otherwise ignore
          the line.

closes: #20126

Supported by AI

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

src/quickfix.c

@@ -1412,7 +1412,6 @@ qf_parse_file_pfx(
 	*fields->namebuf = NUL;
 	if (tail && *tail)
 	{
-	    STRMOVE(IObuff, skipwhite(tail));
 	    qfl->qf_multiscan = TRUE;
 	    return QF_MULTISCAN;
 	}
@@ -1579,7 +1578,15 @@ restofline:
 	{				// global file names
 	    status = qf_parse_file_pfx(idx, fields, qfl, tail);
 	    if (status == QF_MULTISCAN)
+	    {
+		char_u *s = skipwhite(tail);
+		int new_linelen = (int)STRLEN(s);
+		if (new_linelen >= linelen)
+		    return QF_IGNORE_LINE;
+		linebuf = s;
+		linelen = new_linelen;
 		goto restofline;
+	    }
 	}
 	if (fmt_ptr->flags == '-')	// generally exclude this line
 	{

src/testdir/test_quickfix.vim

@@ -7006,4 +7006,26 @@ func Test_quickfix_longline_noeol()
   call assert_equal(['okay'], readfile("XDONE"))
 endfunc
 
+func Test_efm_overlongline()
+  let save_efm = &efm
+  " %r captures the tail.
+  set efm=%+O(%.%#)%r,%f:%l:%m
+
+  " First line is longer than IOSIZE (1025) so the parser puts it in
+  " growbuf; the %r tail then far exceeds IObuff.
+  let lines = ['(short)' .. repeat('x', 4000), 'Xfile:10:msg']
+  call writefile(lines, 'Xqferrlong', 'D')
+
+  " Must complete without hanging or crashing.
+  cgetfile Xqferrlong
+
+  " The well-formed line that follows is still parsed.
+  let well_formed = filter(getqflist(), 'v:val.lnum == 10')
+  call assert_equal(1, len(well_formed))
+  call assert_equal('msg', well_formed[0].text)
+
+  let &efm = save_efm
+  call setqflist([], 'f')
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab

src/version.c

@@ -729,6 +729,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    436,
 /**/
     435,
 /**/