libc: Add support to allow library calls to find appropriate shell executable for a process

Library calls like system() and popen() invoke the shell executable
pointed to by '_PATH_BSHELL' in order to run the command passed into the
function. The _PATH_BSHELL points to /system/bin/sh by default and thus
breaks any vendor process trying to use system() / popen(), as they are
denied access to system shell by selinux.

This CL make necessary changes, so the implmentations of system() and popen()
can use the appropriate shell (e.g. /vendor/bin/sh for processes running
out of /vendor partition). Also, changes the implementation of system()
and popen().

Bug: 64832610
Test: Manual, Using a test program running from /system/bin and
      /vendor/bin to ensure correct shell is being used.

Change-Id: Ie7168d69decb1ae98284446ae7db34dec930dc33
Merged-In: Ie7168d69decb1ae98284446ae7db34dec930dc33
Signed-off-by: Sandeep Patil <sspatil@google.com>
(cherry picked from commit aa3e32422cc7089b9b15976f2651a58840d95e4f)

1 files changed, 4 insertions, 0 deletions

diff --git a/libc/upstream-openbsd/android/include/openbsd-compat.h b/libc/upstream-openbsd/android/include/openbsd-compat.h
index baf505723..d83143583 100644
--- a/libc/upstream-openbsd/android/include/openbsd-compat.h
+++ b/libc/upstream-openbsd/android/include/openbsd-compat.h
@@ -71,6 +71,10 @@ extern const char* __progname;
  */
 #define _PATH_TMP "/data/local/tmp/"
 
+/* Use appropriate shell depending on process's executable. */
+__LIBC_HIDDEN__ extern const char* __bionic_get_shell_path();
+#define _PATH_BSHELL __bionic_get_shell_path()
+
 /* We have OpenBSD's getentropy_linux.c, but we don't mention getentropy in any header. */
 __LIBC_HIDDEN__ extern int getentropy(void*, size_t);