svn commit: r218320 - in head: bin/sh tools/regression/bin/sh/errors

[Jilles Tjoelker]

Author: jilles
Date: Sat Feb  5 12:54:59 2011
New Revision: 218320
URL: http://svn.freebsd.org/changeset/base/218320

Log:
  sh: Do not try to execute binary files as scripts.
  
  If execve() returns an [ENOEXEC] error, check if the file is binary before
  trying to execute it using sh. A file is considered binary if at least one
  of the first 256 bytes is '\0'.
  
  In particular, trying to execute ELF binaries for the wrong architecture now
  fails with an "Exec format error" message instead of syntax errors and
  potentially strange results.

Added:
  head/tools/regression/bin/sh/errors/bad-binary1.126   (contents, props changed)
Modified:
  head/bin/sh/exec.c
  head/bin/sh/sh.1

Modified: head/bin/sh/exec.c
==============================================================================
--- head/bin/sh/exec.c	Sat Feb  5 12:12:51 2011	(r218319)
+++ head/bin/sh/exec.c	Sat Feb  5 12:54:59 2011	(r218320)
@@ -126,6 +126,8 @@ shellexec(char **argv, char **envp, cons
 				tryexec(cmdname, argv, envp);
 				if (errno != ENOENT && errno != ENOTDIR)
 					e = errno;
+				if (e == ENOEXEC)
+					break;
 			}
 			stunalloc(cmdname);
 		}
@@ -145,11 +147,23 @@ shellexec(char **argv, char **envp, cons
 static void
 tryexec(char *cmd, char **argv, char **envp)
 {
-	int e;
+	int e, in;
+	ssize_t n;
+	char buf[256];
 
 	execve(cmd, argv, envp);
 	e = errno;
 	if (e == ENOEXEC) {
+		INTOFF;
+		in = open(cmd, O_RDONLY | O_NONBLOCK);
+		if (in != -1) {
+			n = pread(in, buf, sizeof buf, 0);
+			close(in);
+			if (n > 0 && memchr(buf, '\0', n) != NULL) {
+				errno = ENOEXEC;
+				return;
+			}
+		}
 		*argv = cmd;
 		*--argv = _PATH_BSHELL;
 		execve(_PATH_BSHELL, argv, envp);

Modified: head/bin/sh/sh.1
==============================================================================
--- head/bin/sh/sh.1	Sat Feb  5 12:12:51 2011	(r218319)
+++ head/bin/sh/sh.1	Sat Feb  5 12:54:59 2011	(r218320)
@@ -647,6 +647,7 @@ resulting in an
 .Er ENOEXEC
 return value from
 .Xr execve 2 )
+but appears to be a text file,
 the shell will run a new instance of
 .Nm
 to interpret it.

Added: head/tools/regression/bin/sh/errors/bad-binary1.126
==============================================================================
--- /dev/null	00:00:00 1970	(empty, because file is newly added)
+++ head/tools/regression/bin/sh/errors/bad-binary1.126	Sat Feb  5 12:54:59 2011	(r218320)
@@ -0,0 +1,12 @@
+# $FreeBSD$
+# Checking for binary "scripts" without magic number is permitted but not
+# required by POSIX. However, it is preferable to getting errors like
+# Syntax error: word unexpected (expecting ")")
+# from trying to execute ELF binaries for the wrong architecture.
+
+T=`mktemp -d "${TMPDIR:-/tmp}/sh-test.XXXXXXXX"` || exit
+trap 'rm -rf "${T}"' 0
+printf '\0echo bad\n' >"$T/testshellproc"
+chmod 755 "$T/testshellproc"
+PATH=$T:$PATH
+testshellproc 2>/dev/null