Ignore unreasonably large spacing modifiers in tbl layouts.

Jan Schreiber <jes at posteo dot de> ran afl on mandoc and it turned
out mandoc tried to use spacing modifiers so large that they would
trigger assertion failures in term_ascii.c, function locale_advance().

1 files changed, 6 insertions, 2 deletions

diff --git a/usr.bin/mandoc/mandoc.1 b/usr.bin/mandoc/mandoc.1
index b9a94b7623e..78c5a4c4a5c 100644
--- a/usr.bin/mandoc/mandoc.1
+++ b/usr.bin/mandoc/mandoc.1
@@ -1,4 +1,4 @@
-.\" $OpenBSD: mandoc.1,v 1.172 2020/08/27 15:54:38 schwarze Exp $
+.\" $OpenBSD: mandoc.1,v 1.173 2020/09/01 18:24:09 schwarze Exp $
 .\"
 .\" Copyright (c) 2012, 2014-2020 Ingo Schwarze <schwarze@openbsd.org>
 .\" Copyright (c) 2009, 2010, 2011 Kristaps Dzonsons <kristaps@bsd.lv>
@@ -15,7 +15,7 @@
 .\" ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 .\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 .\"
-.Dd $Mdocdate: August 27 2020 $
+.Dd $Mdocdate: September 1 2020 $
 .Dt MANDOC 1
 .Os
 .Sh NAME
@@ -1850,6 +1850,10 @@ The invalid character is discarded.
 A table layout specification contains an opening parenthesis,
 but no matching closing parenthesis.
 The rest of the input line, starting from the parenthesis, has no effect.
+.It Sy "ignoring excessive spacing in tbl layout"
+.Pq tbl
+A spacing modifier in a table layout is unreasonably large.
+The default spacing of 3n is used instead.
 .It Sy "tbl without any data cells"
 .Pq tbl
 A table does not contain any data cells.