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

(From OE-Core rev: 6f01acae9c279e0a580f46d1ba4c015caa3f8c2c)

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>

2 files changed, 387 insertions, 0 deletions

diff --git a/meta/recipes-extended/bash/bash/bash-CVE-2019-18276.patch b/meta/recipes-extended/bash/bash/bash-CVE-2019-18276.patch
new file mode 100644
index 0000000000..7b2073201e
--- /dev/null
+++ b/meta/recipes-extended/bash/bash/bash-CVE-2019-18276.patch
@@ -0,0 +1,386 @@
+From 951bdaad7a18cc0dc1036bba86b18b90874d39ff Mon Sep 17 00:00:00 2001
+From: Chet Ramey <chet.ramey@case.edu>
+Date: Mon, 1 Jul 2019 09:03:53 -0400
+Subject: [PATCH] commit bash-20190628 snapshot
+
+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.
+
+Upstream-Status: Inappropriate [the upstream thinks it doesn't increase the credibility of CVEs in general]
+CVE: CVE-2019-18276
+
+[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>
+---
+ MANIFEST          |  2 ++
+ bashline.c        | 50 +-------------------------------------------------
+ builtins/help.def |  2 +-
+ config.h.in       | 10 +++++++++-
+ configure.ac      |  1 +
+ doc/bash.1        |  3 ++-
+ doc/bashref.texi  |  3 ++-
+ lib/glob/glob.c   |  5 ++++-
+ pathexp.c         | 16 ++++++++++++++--
+ shell.c           |  8 ++++++++
+ tests/glob.tests  |  2 ++
+ tests/glob6.sub   | 54 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
+ tests/glob7.sub   | 11 +++++++++++
+ 14 files changed, 122 insertions(+), 56 deletions(-)
+ create mode 100644 tests/glob6.sub
+ create mode 100644 tests/glob7.sub
+
+diff --git a/MANIFEST b/MANIFEST
+index 03de221..f9ccad7 100644
+--- a/MANIFEST
++++ b/MANIFEST
+@@ -1037,6 +1037,8 @@ tests/extglob3.tests      f
+ tests/extglob3.right   f
+ tests/extglob4.sub     f
+ tests/extglob5.sub     f
++tests/glob6.sub                f
++tests/glob7.sub                f
+ tests/func.tests       f
+ tests/func.right       f
+ tests/func1.sub                f
+diff --git a/bashline.c b/bashline.c
+index 824ea9d..d86b47d 100644
+--- a/bashline.c
++++ b/bashline.c
+@@ -3718,55 +3718,7 @@ static int
+ completion_glob_pattern (string)
+      char *string;
+ {
+-  register int c;
+-  char *send;
+-  int open;
+-
+-  DECLARE_MBSTATE;
+-
+-  open = 0;
+-  send = string + strlen (string);
+-
+-  while (c = *string++)
+-    {
+-      switch (c)
+-       {
+-       case '?':
+-       case '*':
+-         return (1);
+-
+-       case '[':
+-         open++;
+-         continue;
+-
+-       case ']':
+-         if (open)
+-           return (1);
+-         continue;
+-
+-       case '+':
+-       case '@':
+-       case '!':
+-         if (*string == '(')   /*)*/
+-           return (1);
+-         continue;
+-
+-       case '\\':
+-         if (*string++ == 0)
+-           return (0);           
+-       }
+-
+-      /* Advance one fewer byte than an entire multibyte character to
+-        account for the auto-increment in the loop above. */
+-#ifdef HANDLE_MULTIBYTE
+-      string--;
+-      ADVANCE_CHAR_P (string, send - string);
+-      string++;
+-#else
+-      ADVANCE_CHAR_P (string, send - string);
+-#endif
+-    }
+-  return (0);
++  return (glob_pattern_p (string) == 1);
+ }
+ 
+ static char *globtext;
+diff --git a/builtins/help.def b/builtins/help.def
+index 006c4b5..92f9b38 100644
+--- a/builtins/help.def
++++ b/builtins/help.def
+@@ -128,7 +128,7 @@ help_builtin (list)
+ 
+   /* We should consider making `help bash' do something. */
+ 
+-  if (glob_pattern_p (list->word->word))
++  if (glob_pattern_p (list->word->word) == 1)
+     {
+       printf ("%s", ngettext ("Shell commands matching keyword `", "Shell commands matching keywords `", (list->next ? 2 : 1)));
+       print_word_list (list, ", ");
+diff --git a/config.h.in b/config.h.in
+index 8554aec..ad4b1e8 100644
+--- a/config.h.in
++++ b/config.h.in
+@@ -1,6 +1,6 @@
+ /* config.h -- Configuration file for bash. */
+ 
+-/* Copyright (C) 1987-2009,2011-2012 Free Software Foundation, Inc.
++/* Copyright (C) 1987-2009,2011-2012,2013-2019 Free Software Foundation, Inc.
+ 
+    This file is part of GNU Bash, the Bourne Again SHell.
+ 
+@@ -807,6 +807,14 @@
+ #undef HAVE_SETREGID
+ #undef HAVE_DECL_SETREGID
+ 
++/* Define if you have the setregid function.  */
++#undef HAVE_SETRESGID
++#undef HAVE_DECL_SETRESGID
++
++/* Define if you have the setresuid function.  */
++#undef HAVE_SETRESUID
++#undef HAVE_DECL_SETRESUID
++
+ /* Define if you have the setvbuf function.  */
+ #undef HAVE_SETVBUF
+ 
+diff --git a/configure.ac b/configure.ac
+index 52b4cdb..549adef 100644
+--- a/configure.ac
++++ b/configure.ac
+@@ -810,6 +810,7 @@ AC_CHECK_DECLS([confstr])
+ AC_CHECK_DECLS([printf])
+ AC_CHECK_DECLS([sbrk])
+ AC_CHECK_DECLS([setregid])
++AC_CHECK_DECLS[(setresuid, setresgid])
+ AC_CHECK_DECLS([strcpy])
+ AC_CHECK_DECLS([strsignal])
+ 
+diff --git a/doc/bash.1 b/doc/bash.1
+index e6cd08d..9e58a0b 100644
+--- a/doc/bash.1
++++ b/doc/bash.1
+@@ -4681,7 +4681,8 @@ above).
+ .PD
+ .SH "SIMPLE COMMAND EXPANSION"
+ When a simple command is executed, the shell performs the following
+-expansions, assignments, and redirections, from left to right.
++expansions, assignments, and redirections, from left to right, in
++the following order.
+ .IP 1.
+ The words that the parser has marked as variable assignments (those
+ preceding the command name) and redirections are saved for later
+diff --git a/doc/bashref.texi b/doc/bashref.texi
+index d33cd57..3065126 100644
+--- a/doc/bashref.texi
++++ b/doc/bashref.texi
+@@ -2964,7 +2964,8 @@ is not specified.  If the file does not exist, it is created.
+ @cindex command expansion
+ 
+ When a simple command is executed, the shell performs the following
+-expansions, assignments, and redirections, from left to right.
++expansions, assignments, and redirections, from left to right, in
++the following order.
+ 
+ @enumerate
+ @item
+diff --git a/lib/glob/glob.c b/lib/glob/glob.c
+index 398253b..2eaa33e 100644
+--- a/lib/glob/glob.c
++++ b/lib/glob/glob.c
+@@ -607,6 +607,7 @@ glob_vector (pat, dir, flags)
+   register unsigned int i;
+   int mflags;          /* Flags passed to strmatch (). */
+   int pflags;          /* flags passed to sh_makepath () */
++  int hasglob;         /* return value from glob_pattern_p */
+   int nalloca;
+   struct globval *firstmalloc, *tmplink;
+   char *convfn;
+@@ -648,10 +649,12 @@ glob_vector (pat, dir, flags)
+   patlen = (pat && *pat) ? strlen (pat) : 0;
+ 
+   /* If the filename pattern (PAT) does not contain any globbing characters,
++     or contains a pattern with only backslash escapes (hasglob == 2),
+      we can dispense with reading the directory, and just see if there is
+      a filename `DIR/PAT'.  If there is, and we can access it, just make the
+      vector to return and bail immediately. */
+-  if (skip == 0 && glob_pattern_p (pat) == 0)
++  hasglob = 0;
++  if (skip == 0 && (hasglob = glob_pattern_p (pat)) == 0 || hasglob == 2)
+     {
+       int dirlen;
+       struct stat finfo;
+diff --git a/pathexp.c b/pathexp.c
+index c1bf2d8..e6c5392 100644
+--- a/pathexp.c
++++ b/pathexp.c
+@@ -58,7 +58,10 @@ int extended_glob = EXTGLOB_DEFAULT;
+ /* Control enabling special handling of `**' */
+ int glob_star = 0;
+ 
+-/* Return nonzero if STRING has any unquoted special globbing chars in it.  */
++/* Return nonzero if STRING has any unquoted special globbing chars in it.
++   This is supposed to be called when pathname expansion is performed, so
++   it implements the rules in Posix 2.13.3, specifically that an unquoted
++   slash cannot appear in a bracket expression. */
+ int
+ unquoted_glob_pattern_p (string)
+      register char *string;
+@@ -85,10 +88,14 @@ unquoted_glob_pattern_p (string)
+          continue;
+ 
+        case ']':
+-         if (open)
++         if (open)             /* XXX - if --open == 0? */
+            return (1);
+          continue;
+ 
++       case '/':
++         if (open)
++           open = 0;
++
+        case '+':
+        case '@':
+        case '!':
+@@ -106,6 +113,11 @@ unquoted_glob_pattern_p (string)
+              string++;
+              continue;
+            }
++         else if (open && *string == '/')
++           {
++             string++;         /* quoted slashes in bracket expressions are ok */
++             continue;
++           }
+          else if (*string == 0)
+            return (0);
+                  
+diff --git a/shell.c b/shell.c
+index a2b2a55..6adabc8 100644
+--- a/shell.c
++++ b/shell.c
+@@ -1293,7 +1293,11 @@ disable_priv_mode ()
+ {
+   int e;
+ 
++#if HAVE_DECL_SETRESUID
++  if (setresuid (current_user.uid, current_user.uid, current_user.uid) < 0)
++#else
+   if (setuid (current_user.uid) < 0)
++#endif
+     {
+       e = errno;
+       sys_error (_("cannot set uid to %d: effective uid %d"), current_user.uid, current_user.euid);
+@@ -1302,7 +1306,11 @@ disable_priv_mode ()
+        exit (e);
+ #endif
+     }
++#if HAVE_DECL_SETRESGID
++  if (setresgid (current_user.gid, current_user.gid, current_user.gid) < 0)
++#else
+   if (setgid (current_user.gid) < 0)
++#endif
+     sys_error (_("cannot set gid to %d: effective gid %d"), current_user.gid, current_user.egid);
+ 
+   current_user.euid = current_user.uid;
+diff --git a/tests/glob.tests b/tests/glob.tests
+index 01913bb..fb012f7 100644
+--- a/tests/glob.tests
++++ b/tests/glob.tests
+@@ -12,6 +12,8 @@ ${THIS_SH} ./glob1.sub
+ ${THIS_SH} ./glob2.sub
+ ${THIS_SH} ./glob3.sub
+ ${THIS_SH} ./glob4.sub
++${THIS_SH} ./glob6.sub
++${THIS_SH} ./glob7.sub
+ 
+ MYDIR=$PWD     # save where we are
+ 
+diff --git a/tests/glob6.sub b/tests/glob6.sub
+new file mode 100644
+index 0000000..b099811
+--- /dev/null
++++ b/tests/glob6.sub
+@@ -0,0 +1,54 @@
++# tests of the backslash-in-glob-patterns discussion on the austin-group ML
++
++: ${TMPDIR:=/var/tmp}
++
++ORIG=$PWD
++GLOBDIR=$TMPDIR/bash-glob-$$
++mkdir $GLOBDIR && cd $GLOBDIR
++
++# does the pattern matcher allow backslashes as escape characters and remove
++# them as part of matching?
++touch abcdefg
++pat='ab\cd*'
++printf '<%s>\n' $pat
++pat='\.'
++printf '<%s>\n' $pat
++rm abcdefg
++
++# how about when escaping pattern characters?
++touch '*abc.c'
++a='\**.c'
++printf '%s\n' $a
++rm -f '*abc.c'
++
++# how about when making the distinction between readable and searchable path
++# components?
++mkdir -m a=x searchable
++mkdir -m a=r readable
++
++p='searchable/\.'
++printf "%s\n" $p
++
++p='searchable/\./.'
++printf "%s\n" $p
++
++p='readable/\.'
++printf "%s\n" $p
++
++p='readable/\./.'
++printf "%s\n" $p
++
++printf "%s\n" 'searchable/\.'
++printf "%s\n" 'readable/\.'
++
++echo */.
++
++p='*/\.'
++echo $p
++
++echo */'.'
++
++rmdir searchable readable
++
++cd $ORIG
++rmdir $GLOBDIR
+diff --git a/tests/glob7.sub b/tests/glob7.sub
+new file mode 100644
+index 0000000..0212b8e
+--- /dev/null
++++ b/tests/glob7.sub
+@@ -0,0 +1,11 @@
++# according to Posix 2.13.3, a slash in a bracket expression renders that
++# bracket expression invalid
++shopt -s nullglob
++
++echo 1: [qwe/qwe]
++echo 2: [qwe/
++echo 3: [qwe/]
++
++echo 4: [qwe\/qwe]
++echo 5: [qwe\/
++echo 6: [qwe\/]
+-- 
+1.9.1
+
diff --git a/meta/recipes-extended/bash/bash_5.0.bb b/meta/recipes-extended/bash/bash_5.0.bb
index 12d472be57..257a03bd8b 100644
--- a/meta/recipes-extended/bash/bash_5.0.bb
+++ b/meta/recipes-extended/bash/bash_5.0.bb
@@ -30,6 +30,7 @@ SRC_URI = "${GNU_MIRROR}/bash/${BP}.tar.gz;name=tarball \
            file://run-ptest \
            file://run-bash-ptests \
            file://fix-run-builtins.patch \
+           file://bash-CVE-2019-18276.patch \
            "
 
 SRC_URI[tarball.md5sum] = "2b44b47b905be16f45709648f671820b"