CVE-2018-0502, CVE-2018-13259: Fix two security issues in shebang line parsing.

See NEWS for more information.

Patch by Anthony Sottile and Buck Evan.

ChangeLog

@@ -1,3 +1,8 @@
+2018-09-03  Anthony Sottile  <asottile@umich.edu>
+
+	* CVE-2018-0502, CVE-2018-13259: Fix two security issues in
+	shebang line parsing. [With Buck Evan]
+
 2018-09-03  Daniel Shahaf  <d.s@daniel.shahaf.name>
 
 	* 43367: Makefile.in: Add maintainer targets 'tarxz-src' and

Etc/FAQ.yo

@@ -306,7 +306,7 @@ sect(On what machines will it run?)
 
 sect(What's the latest version?)
 
-  Zsh 5.5.1 is the latest production version.  For details of all the
+  Zsh 5.6 is the latest production version.  For details of all the
   changes, see the NEWS file in the source distribution.
 
   A beta of the next version is sometimes available.  Development of zsh is

NEWS

@@ -4,6 +4,27 @@ CHANGES FROM PREVIOUS VERSIONS OF ZSH
 
 Note also the list of incompatibilities in the README file.
 
+Changes from 5.5.1-test-2 to 5.6
+--------------------------------
+
+CVE-2018-0502: Data from the second line of a #! script file might be passed to
+execve().  For example, in the following situation -
+.
+    printf '#!foo\nbar' > baz
+    ./baz
+.
+the shell might take "bar" rather than "foo" for the argv[0] to be passed to
+execve().  [ Reported by Anthony Sottile and Buck Evan. ]
+
+CVE-2018-13259: A shebang line longer than 64 characters would be truncated.
+For example, in the following situation:
+.
+    ( printf '#!'; repeat 64 printf 'x'; printf 'y' ) > foo
+    ./foo
+.
+the shell might execute x...x (64 repetitions) rather than x...xy (64 x's,
+one y).  [ Reported by Daniel Shahaf. ]
+
 Changes from 5.5.1 to 5.5.1-test-2
 ----------------------------------
 

README

@@ -5,9 +5,9 @@ THE Z SHELL (ZSH)
 Version
 -------
 
-This is version 5.5.1-test-2 of the shell.  This is a test release.  There
-are some significant bug fixes and a few user visible additions since
-5.5.1.  All zsh installations are encouraged to upgrade.
+This is version 5.6 of the shell.  This is a security and feature release.
+There are some significant bug fixes and a few user visible additions since
+5.5.1.  All zsh installations are encouraged to upgrade as soon as possible.
 
 Note in particular the changes highlighted under "Incompatibilities since
 5.5.1" below.  See NEWS for more information.

Src/exec.c

@@ -458,7 +458,7 @@ execcursh(Estate state, int do_exec)
 
 /* execve after handling $_ and #! */
 
-#define POUNDBANGLIMIT 64
+#define POUNDBANGLIMIT 128
 
 /**/
 static int
@@ -499,18 +499,20 @@ zexecve(char *pth, char **argv, char **newenvp)
 	if ((fd = open(pth, O_RDONLY|O_NOCTTY)) >= 0) {
 	    argv0 = *argv;
 	    *argv = pth;
-	    execvebuf[0] = '\0';
+	    memset(execvebuf, '\0', POUNDBANGLIMIT + 1);
 	    ct = read(fd, execvebuf, POUNDBANGLIMIT);
 	    close(fd);
 	    if (ct >= 0) {
-		if (execvebuf[0] == '#') {
-		    if (execvebuf[1] == '!') {
-			for (t0 = 0; t0 != ct; t0++)
-			    if (execvebuf[t0] == '\n')
-				break;
+		if (ct >= 2 && execvebuf[0] == '#' && execvebuf[1] == '!') {
+		    for (t0 = 0; t0 != ct; t0++)
+			if (execvebuf[t0] == '\n')
+			    break;
+		    if (t0 == ct)
+			zerr("%s: bad interpreter: %s: %e", pth,
+			     execvebuf + 2, eno);
+		    else {
 			while (inblank(execvebuf[t0]))
 			    execvebuf[t0--] = '\0';
-			execvebuf[POUNDBANGLIMIT] = '\0';
 			for (ptr = execvebuf + 2; *ptr && *ptr == ' '; ptr++);
 			for (ptr2 = ptr; *ptr && *ptr != ' '; ptr++);
 			if (eno == ENOENT) {
@@ -519,10 +521,16 @@ zexecve(char *pth, char **argv, char **newenvp)
 				*ptr = '\0';
 			    if (*ptr2 != '/' &&
 				(pprog = pathprog(ptr2, NULL))) {
-				argv[-2] = ptr2;
-				argv[-1] = ptr + 1;
-				winch_unblock();
-				execve(pprog, argv - 2, newenvp);
+				if (ptr == execvebuf + t0 + 1) {
+				    argv[-1] = ptr2;
+				    winch_unblock();
+				    execve(pprog, argv - 1, newenvp);
+				} else {
+				    argv[-2] = ptr2;
+				    argv[-1] = ptr + 1;
+				    winch_unblock();
+				    execve(pprog, argv - 2, newenvp);
+				}
 			    }
 			    zerr("%s: bad interpreter: %s: %e", pth, ptr2,
 				 eno);
@@ -537,10 +545,6 @@ zexecve(char *pth, char **argv, char **newenvp)
 			    winch_unblock();
 			    execve(ptr2, argv - 1, newenvp);
 			}
-		    } else if (eno == ENOEXEC) {
-			argv[-1] = "sh";
-			winch_unblock();
-			execve("/bin/sh", argv - 1, newenvp);
 		    }
 		} else if (eno == ENOEXEC) {
 		    for (t0 = 0; t0 != ct; t0++)

Test/A05execution.ztst

@@ -12,7 +12,14 @@
 
   print '#!/bin/sh\necho This is dir2' >dir2/tstcmd
 
+  print -n '#!sh\necho This is slashless' >tstcmd-slashless
+  print -n '#!echo foo\necho This is arg' >tstcmd-arg
+  print '#!xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxnyyy' >tstcmd-interp-too-long
+  print '#!/bin/sh\necho should not execute; exit 1' >xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxn
+
   chmod 755 tstcmd dir1/tstcmd dir2/tstcmd
+  chmod 755 tstcmd-slashless tstcmd-arg tstcmd-interp-too-long
+  chmod 755 xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxn
 
 %test
   ./tstcmd
@@ -33,6 +40,21 @@
 0:path (2)
 >This is top
 
+  PATH=/bin:${ZTST_testdir}/command.tmp/ tstcmd-slashless
+0:path (3)
+>This is slashless
+
+  PATH=/bin:${ZTST_testdir}/command.tmp tstcmd-arg
+0:path (4)
+*>foo */command.tmp/tstcmd-arg
+
+  path=(/bin ${ZTST_testdir}/command.tmp/)
+  tstcmd-interp-too-long 2>&1; echo "status $?"
+  path=($storepath)
+0:path (5)
+*>*tstcmd-interp-too-long: bad interpreter: x*xn: no such file or directory
+>status 127
+
   functst() { print $# arguments:; print -l $*; }
   functst "Eines Morgens" "als Gregor Samsa"
   functst ""