From c7a9cf465dd620ef48d586026944d9bd7a0d5d6d Mon Sep 17 00:00:00 2001
From: Peter Stephenson <pws@zsh.org>
Date: Tue, 9 May 2017 17:49:18 +0100
Subject: 40181: Fix buffer overrun in xsymlinks.

There was no check for copying to the internal xbuf2 for a
preliminary test.
---
 ChangeLog         |  3 +++
 Src/utils.c       | 14 +++++++++++---
 Test/D02glob.ztst |  8 ++++++++
 3 files changed, 22 insertions(+), 3 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index 82d4a7086..ee6e918db 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,8 @@
 2017-05-09  Peter Stephenson  <p.stephenson@samsung.com>
 
+	* 41081: Src/utils.c, Test/D02glob.ztst: Symlink expansion
+	didn't test all buffer length calculations.
+
 	* 41078: Src/prompt.c, Test/D01prompt.ztst: Empty psvar could
 	cause bad reference in prompt expansion.
 
diff --git a/Src/utils.c b/Src/utils.c
index ea4b34bab..5eb936bed 100644
--- a/Src/utils.c
+++ b/Src/utils.c
@@ -886,7 +886,7 @@ xsymlinks(char *s, int full)
     char **pp, **opp;
     char xbuf2[PATH_MAX*3+1], xbuf3[PATH_MAX*2+1];
     int t0, ret = 0;
-    zulong xbuflen = strlen(xbuf);
+    zulong xbuflen = strlen(xbuf), pplen;
 
     opp = pp = slashsplit(s);
     for (; xbuflen < sizeof(xbuf) && *pp && ret >= 0; pp++) {
@@ -907,10 +907,18 @@ xsymlinks(char *s, int full)
 	    xbuflen--;
 	    continue;
 	}
-	sprintf(xbuf2, "%s/%s", xbuf, *pp);
+	/* Includes null byte. */
+	pplen = strlen(*pp) + 1;
+	if (xbuflen + pplen + 1 > sizeof(xbuf2)) {
+	    *xbuf = 0;
+	    ret = -1;
+	    break;
+	}
+	memcpy(xbuf2, xbuf, xbuflen);
+	xbuf2[xbuflen] = '/';
+	memcpy(xbuf2 + xbuflen + 1, *pp, pplen);
 	t0 = readlink(unmeta(xbuf2), xbuf3, PATH_MAX);
 	if (t0 == -1) {
-	    zulong pplen = strlen(*pp) + 1;
 	    if ((xbuflen += pplen) < sizeof(xbuf)) {
 		strcat(xbuf, "/");
 		strcat(xbuf, *pp);
diff --git a/Test/D02glob.ztst b/Test/D02glob.ztst
index 413381f92..0ff696807 100644
--- a/Test/D02glob.ztst
+++ b/Test/D02glob.ztst
@@ -687,6 +687,14 @@
 0:modifier ':P' resolves symlinks before '..' components
 *>*glob.tmp/hello/world
 
+ # This is a bit brittle as it depends on PATH_MAX.
+ # We could use sysconf..
+ bad_pwd="/${(l:16000:: :):-}"
+ print ${bad_pwd:P}
+0:modifier ':P' with path too long
+?(eval):2: path expansion failed, using root directory
+>/
+
  foo=a
  value="ac"
  print ${value//[${foo}b-z]/x}
-- 
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