From: Pádraig Brady <P@draigBrady.com>
Date: Mon, 28 Nov 2016 17:11:18 +0000 (+0000)
Subject: head: fix processing of non-seekable input as seekable
X-Git-Tag: v8.26~4
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=0655b86a6ebc6f1324810d504a71803aa708d162;p=thirdparty%2Fcoreutils.git

head: fix processing of non-seekable input as seekable

* src/head.c (elide_tail_bytes_file): Ensure we don't use
st_size unless we've previously used seek() to determine
the CURRENT_POS in the seekable file.
This was seen to cause issue on FreeBSD 11 when the pipe
buffer was filled with `yes | head --lines=-0`, in which
case st_size was 64KiB while ST_BLKSIZE() was 4KiB.
Reported by Assaf Gordon.
---

diff --git a/NEWS b/NEWS
index e88e932145..ea84a4dba4 100644
--- a/NEWS
+++ b/NEWS
@@ -25,6 +25,10 @@ GNU coreutils NEWS                                    -*- outline -*-
   factor again outputs immediately when numbers are input interactively.
   [bug introduced in coreutils-8.24]
 
+  head no longer tries to process non-seekable input as seekable,
+  which resulted in failures on FreeBSD 11 at least.
+  [bug introduced in coreutils-8.24]
+
   install -DZ and mkdir -pZ now set default SELinux context correctly even if
   two or more directories nested in each other are created and each of them
   defaults to a different SELinux context.
diff --git a/src/head.c b/src/head.c
index 21ace70b41..756c978c61 100644
--- a/src/head.c
+++ b/src/head.c
@@ -465,7 +465,7 @@ elide_tail_bytes_file (const char *filename, int fd, uintmax_t n_elide,
                        struct stat const *st, off_t current_pos)
 {
   off_t size = st->st_size;
-  if (presume_input_pipe || size <= ST_BLKSIZE (*st))
+  if (presume_input_pipe || current_pos < 0 || size <= ST_BLKSIZE (*st))
     return elide_tail_bytes_pipe (filename, fd, n_elide, current_pos);
   else
     {
@@ -754,7 +754,7 @@ elide_tail_lines_file (const char *filename, int fd, uintmax_t n_elide,
                        struct stat const *st, off_t current_pos)
 {
   off_t size = st->st_size;
-  if (presume_input_pipe || size <= ST_BLKSIZE (*st))
+  if (presume_input_pipe || current_pos < 0 || size <= ST_BLKSIZE (*st))
     return elide_tail_lines_pipe (filename, fd, n_elide, current_pos);
   else
     {