See <http://lists.gnu.org/archive/html/bug-patch/2015-06/msg00009.html>

From 0507dfad5f060161f01840067e1bb1615257b636 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Ludovic=20Court=C3=A8s?= <ludo@gnu.org>
Date: Mon, 8 Jun 2015 17:27:56 +0200
Subject: [PATCH] Do not rely on PATH_MAX when reading a symlink target.

* src/util.c (move_file, copy_file): Use 'fromst->st_size + 1' and
'tost->st_size + 1' for the allocation, and 'fromst->st_size' and
'tost->st_size' instead of PATH_MAX.  Fixes compilation on GNU/Hurd.
---
 src/util.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/src/util.c b/src/util.c
index 82a7e37..c4c0f9d 100644
--- a/src/util.c
+++ b/src/util.c
@@ -460,12 +460,12 @@ move_file (char const *from, bool *from_needs_removal,
 
 	  /* FROM contains the contents of the symlink we have patched; need
 	     to convert that back into a symlink. */
-	  char *buffer = xmalloc (PATH_MAX);
+	  char *buffer = xmalloc (fromst->st_size + 1);
 	  int fd, size = 0, i;
 
 	  if ((fd = safe_open (from, O_RDONLY | O_BINARY, 0)) < 0)
 	    pfatal ("Can't reopen file %s", quotearg (from));
-	  while ((i = read (fd, buffer + size, PATH_MAX - size)) > 0)
+	  while ((i = read (fd, buffer + size, fromst->st_size - size)) > 0)
 	    size += i;
 	  if (i != 0 || close (fd) != 0)
 	    read_fatal ();
@@ -610,9 +610,9 @@ copy_file (char const *from, char const *to, struct stat *tost,
 
   if (S_ISLNK (mode))
     {
-      char *buffer = xmalloc (PATH_MAX);
+      char *buffer = xmalloc (tost->st_size + 1);
 
-      if (safe_readlink (from, buffer, PATH_MAX) < 0)
+      if (safe_readlink (from, buffer, tost->st_size) < 0)
 	pfatal ("Can't read %s %s", "symbolic link", from);
       if (safe_symlink (buffer, to) != 0)
 	pfatal ("Can't create %s %s", "symbolic link", to);
-- 
2.4.2

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<div class='path'>path: <a href='/guix/log/?id=b1d2e0b4e0a22c1cdda376b1c9950f14ca99230e'>root</a>/<a href='/guix/log/gnu?id=b1d2e0b4e0a22c1cdda376b1c9950f14ca99230e'>gnu</a>/<a href='/guix/log/gnu/packages?id=b1d2e0b4e0a22c1cdda376b1c9950f14ca99230e'>packages</a>/<a href='/guix/log/gnu/packages/nano.scm?id=b1d2e0b4e0a22c1cdda376b1c9950f14ca99230e'>nano.scm</a></div><div class='content'><table class='list nowrap'><tr class='nohover'><th class='left'>Age</th><th class='left'>Commit message (<a href='/guix/log/gnu/packages/nano.scm?id=b1d2e0b4e0a22c1cdda376b1c9950f14ca99230e&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2018-11-14 21:05:30 +0100'>2018-11-14</span></td><td><a href='/guix/commit/gnu/packages/nano.scm?id=7939387da83437918b87d00b06b19b7c987ed171'>gnu: nano: Update to 3.2.</a><span class='msg-avail'>...</span></td><td>Marius Bakke</td></tr>
<tr><td><span title='2018-09-24 00:33:59 +0200'>2018-09-24</span></td><td><a href='/guix/commit/gnu/packages/nano.scm?id=0604d3cfceea13fad33c6188fa54f5fd16c74406'>gnu: nano: Update to 3.1.</a><span class='msg-avail'>...</span></td><td>Tobias Geerinckx-Rice</td></tr>
<tr><td><span title='2018-09-10 13:54:29 -0400'>2018-09-10</span></td><td><a href='/guix/commit/gnu/packages/nano.scm?id=254844f22d81356ee00977e95640245281257661'>gnu: nano: Update to 3.0.</a><span class='msg-avail'>...</span></td><td>Leo Famulari</td></tr>
<tr><td><span title='2018-06-05 03:18:46 +0200'>2018-06-05</span></td><td><a href='/guix/commit/gnu/packages/nano.scm?id=123f86d8989cc787cddeb2ffd3c3640e29d56c9d'>gnu: nano: Update to 2.9.8.</a><span class='msg-avail'>...</span></td><td>Tobias Geerinckx-Rice</td></tr>
<tr><td><span title='2018-05-15 22:24:07 -0500'>2018-05-15</span></td><td><a href='/guix/commit/gnu/packages/nano.scm?id=5f93600fa62d5fa1e47e273ec347ee14e72f7170'>gnu: nano: Update to 2.9.7.</a><span class='msg-avail'>...</span></td><td>Eric Bavier</td></tr>
<tr><td><span title='2018-05-01 16:01:39 +0200'>2018-05-01</span></td><td><a href='/guix/commit/gnu/packages/nano.scm?id=4336e36c943a31c7c02cc74cbb0212787c77e0f8'>gnu: nano: Update to 2.9.6.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2018-03-29 16:08:06 +0300'>2018-03-29</span></td><td><a href='/guix/commit/gnu/packages/nano.scm?id=594e5d73688bb75fe5efc6ae3c27b4689e16726d'>gnu: nano: Update to 2.9.5.</a><span class='msg-avail'>...</span></td><td>Efraim Flashner</td></tr>
<tr><td><span title='2018-03-08 20:29:20 +0200'>2018-03-08</span></td><td><a href='/guix/commit/gnu/packages/nano.scm?id=fee7f8a94ec64943109ba9c37f75c28749fb18bd'>gnu: nano: Update to 2.9.4.</a><span class='msg-avail'>...</span></td><td>Efraim Flashner</td></tr>