From a944b682a694b4e7900c94d6550845f8d52af574 Mon Sep 17 00:00:00 2001
From: Michael Forney <mforney@mforney.org>
Date: Sat, 14 May 2016 18:56:54 -0700
Subject: [PATCH] sort: Fix line comparison when col buffer contains data from
 longer line

I'm not sure if there are other implications of this or not, but
the issue is that columns() uses len to store the allocated buffer
size, but linecmp() compares up to len bytes. If those trailing
bytes do not match, the line is considered not matching, even though
the relevant parts of the buffer do match.

To resolve this, also keep track of column capacity. Additionally,
since there is no reason to keep the existing data when resizing,
just use free and emalloc rather than erealloc.

The simplest case I could reduce it to is this:

if [ "$(printf '%s\n' a a xxb xxc | ./sort -u)" = "$(printf '%s\n' a xxb xxc)" ] ; then
	echo pass
else
	echo fail
fi
---
 sort.c | 37 ++++++++++++++++++++-----------------
 1 file changed, 20 insertions(+), 17 deletions(-)

diff --git a/sort.c b/sort.c
index 90ee911..623b81e 100644
--- a/sort.c
+++ b/sort.c
@@ -18,6 +18,11 @@ struct keydef {
 	TAILQ_ENTRY(keydef) entry;
 };
 
+struct column {
+	struct line line;
+	size_t cap;
+};
+
 enum {
 	MOD_N      = 1 << 0,
 	MOD_STARTB = 1 << 1,
@@ -33,7 +38,7 @@ static TAILQ_HEAD(kdhead, keydef) kdhead = TAILQ_HEAD_INITIALIZER(kdhead);
 static int Cflag = 0, cflag = 0, uflag = 0;
 static char *fieldsep = NULL;
 static size_t fieldseplen = 0;
-static struct line col1, col2;
+static struct column col1, col2;
 
 static void
 skipblank(struct line *a)
@@ -76,12 +81,12 @@ skipcolumn(struct line *a, int skip_to_next_col)
 	}
 }
 
-static size_t
-columns(struct line *line, const struct keydef *kd, struct line *col)
+static void
+columns(struct line *line, const struct keydef *kd, struct column *col)
 {
 	Rune r;
 	struct line start, end;
-	size_t len, utflen, rlen;
+	size_t utflen, rlen;
 	int i;
 
 	start.data = line->data;
@@ -118,15 +123,13 @@ columns(struct line *line, const struct keydef *kd, struct line *col)
 		end.data += end.len - 1;
 		end.len = 1;
 	}
-	len = MAX(0, end.data - start.data);
-	if (!(col->data) || col->len < len)
-		col->data = erealloc(col->data, len + 1);
-	memcpy(col->data, start.data, len);
-	col->data[len] = '\0';
-	if (col->len < len)
-		col->len = len;
-
-	return len;
+	col->line.len = MAX(0, end.data - start.data);
+	if (!(col->line.data) || col->cap < col->line.len + 1) {
+		free(col->line.data);
+		col->line.data = emalloc(col->line.len + 1);
+	}
+	memcpy(col->line.data, start.data, col->line.len);
+	col->line.data[col->line.len] = '\0';
 }
 
 static int
@@ -187,13 +190,13 @@ slinecmp(struct line *a, struct line *b)
 		    TAILQ_LAST(&kdhead, kdhead) != TAILQ_FIRST(&kdhead)) {
 			res = 0;
 		} else if (kd->flags & MOD_N) {
-			x = strtold(col1.data, NULL);
-			y = strtold(col2.data, NULL);
+			x = strtold(col1.line.data, NULL);
+			y = strtold(col2.line.data, NULL);
 			res = (x < y) ? -1 : (x > y);
 		} else if (kd->flags & (MOD_D | MOD_F | MOD_I)) {
-			res = skipmodcmp(&col1, &col2, kd->flags);
+			res = skipmodcmp(&col1.line, &col2.line, kd->flags);
 		} else {
-			res = linecmp(&col1, &col2);
+			res = linecmp(&col1.line, &col2.line);
 		}
 
 		if (kd->flags & MOD_R)