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From 906e92715f4ee68ea95086867f4f97b1f4f10ac3 Mon Sep 17 00:00:00 2001
From: Tony Cook <tony@develop-help.com>
Date: Tue, 3 Oct 2023 09:40:07 +1100
Subject: [PATCH] win32: default the shell to cmd.exe in the Windows system
directory
This prevents picking up cmd.exe from the current directory, or
even from the PATH.
This protects against a privilege escalation attack where an attacker
in a separate session creates a cmd.exe in a directory where the
target account happens to have its current directory.
---
t/win32/system.t | 30 ++++++++++++--------
win32/win32.c | 71 +++++++++++++++++++++++++++++++++++++++++-------
2 files changed, 79 insertions(+), 22 deletions(-)
diff --git a/t/win32/system.t b/t/win32/system.t
index 939a02db55..c885059012 100644
--- a/t/win32/system.t
+++ b/t/win32/system.t
@@ -82,6 +82,7 @@ close $F;
chdir($testdir);
END {
chdir($cwd) && rmtree("$cwd/$testdir") if -d "$cwd/$testdir";
+ unlink "cmd.exe";
}
if (open(my $EIN, "$cwd/win32/${exename}_exe.uu")) {
note "Unpacking $exename.exe";
@@ -104,21 +105,20 @@ else {
}
note "Compiling $exename.c";
note "$Config{cc} $Config{ccflags} $exename.c";
- if (system("$Config{cc} $Config{ccflags} $minus_o $exename.c >log 2>&1") != 0) {
+ if (system("$Config{cc} $Config{ccflags} $minus_o $exename.c >log 2>&1") != 0 ||
+ !-f "$exename.exe") {
note "Could not compile $exename.c, status $?";
- note "Where is your C compiler?";
- skip_all "can't build test executable";
- }
- unless (-f "$exename.exe") {
- if (open(LOG,'<log'))
- {
- while(<LOG>) {
- note $_;
- }
- }
+ note "Where is your C compiler?";
+ if (open(LOG,'<log'))
+ {
+ while(<LOG>) {
+ note $_;
+ }
+ }
else {
- warn "Cannot open log (in $testdir):$!";
+ warn "Cannot open log (in $testdir):$!";
}
+ skip_all "can't build test executable";
}
}
copy("$plxname.bat","$plxname.cmd");
@@ -128,6 +128,12 @@ unless (-x "$testdir/$exename.exe") {
skip_all "can't build test executable";
}
+# test we only look for cmd.exe in the standard place
+delete $ENV{PERLSHELL};
+copy("$testdir/$exename.exe", "$testdir/cmd.exe") or die $!;
+copy("$testdir/$exename.exe", "cmd.exe") or die $!;
+$ENV{PATH} = qq("$testdir";$ENV{PATH});
+
open my $T, "$^X -I../lib -w win32/system_tests |"
or die "Can't spawn win32/system_tests: $!";
my $expect;
diff --git a/win32/win32.c b/win32/win32.c
index 94248ca168..5d54cf8d4a 100644
--- a/win32/win32.c
+++ b/win32/win32.c
@@ -117,7 +117,7 @@ static char* win32_get_xlib(const char *pl,
static BOOL has_shell_metachars(const char *ptr);
static long tokenize(const char *str, char **dest, char ***destv);
-static void get_shell(void);
+static int get_shell(void);
static char* find_next_space(const char *s);
static int do_spawn2(pTHX_ const char *cmd, int exectype);
static int do_spawn2_handles(pTHX_ const char *cmd, int exectype,
@@ -600,7 +600,13 @@ tokenize(const char *str, char **dest, char ***destv)
return items;
}
-static void
+static const char
+cmd_opts[] = "/x/d/c";
+
+static const char
+shell_cmd[] = "cmd.exe";
+
+static int
get_shell(void)
{
dTHX;
@@ -612,12 +618,53 @@ get_shell(void)
* interactive use (which is what most programs look in COMSPEC
* for).
*/
- const char* defaultshell = "cmd.exe /x/d/c";
- const char *usershell = PerlEnv_getenv("PERL5SHELL");
- w32_perlshell_items = tokenize(usershell ? usershell : defaultshell,
- &w32_perlshell_tokens,
- &w32_perlshell_vec);
+ const char *shell = PerlEnv_getenv("PERL5SHELL");
+ if (shell) {
+ w32_perlshell_items = tokenize(shell,
+ &w32_perlshell_tokens,
+ &w32_perlshell_vec);
+ }
+ else {
+ /* tokenize does some Unix-ish like things like
+ \\ escaping that don't work well here
+ */
+ char shellbuf[MAX_PATH];
+ UINT len = GetSystemDirectoryA(shellbuf, sizeof(shellbuf));
+ if (len == 0) {
+ translate_to_errno();
+ return -1;
+ }
+ else if (len >= MAX_PATH) {
+ /* buffer too small */
+ errno = E2BIG;
+ return -1;
+ }
+ if (shellbuf[len-1] != '\\') {
+ my_strlcat(shellbuf, "\\", sizeof(shellbuf));
+ ++len;
+ }
+ if (len + sizeof(shell_cmd) > sizeof(shellbuf)) {
+ errno = E2BIG;
+ return -1;
+ }
+ my_strlcat(shellbuf, shell_cmd, sizeof(shellbuf));
+ len += sizeof(shell_cmd)-1;
+
+ Newx(w32_perlshell_vec, 3, char *);
+ Newx(w32_perlshell_tokens, len + 1 + sizeof(cmd_opts), char);
+
+ my_strlcpy(w32_perlshell_tokens, shellbuf, len+1);
+ my_strlcpy(w32_perlshell_tokens + len +1, cmd_opts,
+ sizeof(cmd_opts));
+
+ w32_perlshell_vec[0] = w32_perlshell_tokens;
+ w32_perlshell_vec[1] = w32_perlshell_tokens + len + 1;
+ w32_perlshell_vec[2] = NULL;
+
+ w32_perlshell_items = 2;
+ }
}
+ return 0;
}
int
@@ -635,7 +682,9 @@ Perl_do_aspawn(pTHX_ SV *really, SV **mark, SV **sp)
if (sp <= mark)
return -1;
- get_shell();
+ if (get_shell() < 0)
+ return -1;
+
Newx(argv, (sp - mark) + w32_perlshell_items + 2, const char*);
if (SvNIOKp(*(mark+1)) && !SvPOKp(*(mark+1))) {
@@ -765,7 +814,8 @@ do_spawn2_handles(pTHX_ const char *cmd, int exectype, const int *handles)
if (needToTry) {
char **argv;
int i = -1;
- get_shell();
+ if (get_shell() < 0)
+ return -1;
Newx(argv, w32_perlshell_items + 2, char*);
while (++i < w32_perlshell_items)
argv[i] = w32_perlshell_vec[i];
@@ -3482,7 +3532,8 @@ win32_pipe(int *pfd, unsigned int size, int mode)
DllExport PerlIO*
win32_popenlist(const char *mode, IV narg, SV **args)
{
- get_shell();
+ if (get_shell() < 0)
+ return NULL;
return do_popen(mode, NULL, narg, args);
}
--
2.33.0
|
