From d23662ec2e738098f5af6e978dbd3ea5484fc155 Mon Sep 17 00:00:00 2001
From: Alan Somers <asomers@FreeBSD.org>
Date: Mon, 19 Feb 2018 22:09:49 +0000
Subject: [PATCH] tail: fix "tail -r" for piped input that begins with '\n'

A subtle logic bug, probably introduced in r311895, caused tail to print the
first two lines of piped input in forward order, if the very first character
was a newline.

PR:		222671
Reported by:	Jim Long <freebsd-bugzilla@umpquanet.com>, pprocacci@gmail.com
MFC after:	3 weeks
Sponsored by:	Spectra Logic Corp
---
 usr.bin/tail/reverse.c          |  7 ++++--
 usr.bin/tail/tests/tail_test.sh | 44 +++++++++++++++++++++++++++++++++
 2 files changed, 49 insertions(+), 2 deletions(-)

diff --git a/usr.bin/tail/reverse.c b/usr.bin/tail/reverse.c
index 435623b594ae..422724c0ebab 100644
--- a/usr.bin/tail/reverse.c
+++ b/usr.bin/tail/reverse.c
@@ -257,10 +257,13 @@ r_buf(FILE *fp, const char *fn)
 			if ((*p == '\n') || start) {
 				struct bfelem *tr;
 
-				if (start && llen)
+				if (llen && start && *p != '\n')
 					WR(p, llen + 1);
-				else if (llen)
+				else if (llen) {
 					WR(p + 1, llen);
+					if (start && *p == '\n')
+						WR(p, 1);
+				}
 				tr = TAILQ_NEXT(tl, entries);
 				llen = 0;
 				if (tr != NULL) {
diff --git a/usr.bin/tail/tests/tail_test.sh b/usr.bin/tail/tests/tail_test.sh
index fddc4ccd998b..d136a0be605e 100755
--- a/usr.bin/tail/tests/tail_test.sh
+++ b/usr.bin/tail/tests/tail_test.sh
@@ -83,6 +83,49 @@ HERE
 	atf_check cmp expectfile outpipe
 }
 
+# Regression test for PR 222671
+# https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=222671
+atf_test_case pipe_leading_newline_r
+pipe_leading_newline_r_head()
+{
+	atf_set "descr" "Reverse a pipe whose first character is a newline"
+}
+pipe_leading_newline_r_body()
+{
+	cat > expectfile << HERE
+3
+2
+1
+
+HERE
+	printf '\n1\n2\n3\n' | tail -r > outfile
+	printf '\n1\n2\n3\n' | tail -r > outpipe
+	atf_check cmp expectfile outfile
+	atf_check cmp expectfile outpipe
+}
+
+atf_test_case file_rc28
+file_rc28_head()
+{
+	atf_set "descr" "Reverse a file and display the last 28 characters"
+}
+file_rc28_body()
+{
+	cat > infile <<HERE
+This is the first line
+This is the second line
+This is the third line
+HERE
+	cat > expectfile << HERE
+This is the third line
+line
+HERE
+	tail -rc28 infile > outfile
+	tail -rc28 < infile > outpipe
+	atf_check cmp expectfile outfile
+	atf_check cmp expectfile outpipe
+}
+
 atf_test_case file_rc28
 file_rc28_head()
 {
@@ -235,6 +278,7 @@ atf_init_test_cases()
 	atf_add_test_case file_r
 	atf_add_test_case file_rc28
 	atf_add_test_case file_rn2
+	atf_add_test_case pipe_leading_newline_r
 	# The longfile tests are designed to exercise behavior in r_buf(),
 	# which operates on 128KB blocks
 	atf_add_test_case longfile_r