bash: fix CVE-2019-18276

An issue was discovered in disable_priv_mode in shell.c in GNU Bash
through 5.0 patch 11. By default, if Bash is run with its effective UID
not equal to its real UID, it will drop privileges by setting its
effective UID to its real UID. However, it does so incorrectly. On Linux
and other systems that support "saved UID" functionality, the saved UID
is not dropped. An attacker with command execution in the shell can use
"enable -f" for runtime loading of a new builtin, which can be a shared
object that calls setuid() and therefore regains privileges. However,
binaries running with an effective UID of 0 are unaffected.

Get the patch from [1] to fix the issue.

[1] https://git.savannah.gnu.org/cgit/bash.git/commit/?h=devel&id=951bdaa



Signed-off-by: De Huo <De.Huo@windriver.com>
Signed-off-by: Kai Kang <kai.kang@windriver.com>
Signed-off-by: Mingli Yu <mingli.yu@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>