docs: kernel_feat.py: fix potential command injection

The kernel-feat directive passes its argument straight to the shell.
This is unfortunate and unnecessary.

Let's always use paths relative to $srctree/Documentation/ and use
subprocess.check_call() instead of subprocess.Popen(shell=True).

This also makes the code shorter.

This is analogous to commit 3231dd586277 ("docs: kernel_abi.py: fix
command injection") where we did exactly the same thing for
kernel_abi.py, somehow I completely missed this one.

Link: https://fosstodon.org/@jani/111676532203641247
Reported-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Vegard Nossum <vegard.nossum@oracle.com>
Cc: stable@vger.kernel.org
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/20240110174758.3680506-1-vegard.nossum@oracle.com

1 files changed, 11 insertions, 44 deletions

diff --git a/Documentation/sphinx/kernel_feat.py b/Documentation/sphinx/kernel_feat.py
index b5fa2f0542a5d..b9df61eb45013 100644
--- a/Documentation/sphinx/kernel_feat.py
+++ b/Documentation/sphinx/kernel_feat.py
@@ -37,8 +37,6 @@ import re
 import subprocess
 import sys
 
-from os import path
-
 from docutils import nodes, statemachine
 from docutils.statemachine import ViewList
 from docutils.parsers.rst import directives, Directive
@@ -76,33 +74,26 @@ class KernelFeat(Directive):
         self.state.document.settings.env.app.warn(message, prefix="")
 
     def run(self):
-
         doc = self.state.document
         if not doc.settings.file_insertion_enabled:
             raise self.warning("docutils: file insertion disabled")
 
         env = doc.settings.env
-        cwd = path.dirname(doc.current_source)
-        cmd = "get_feat.pl rest --enable-fname --dir "
-        cmd += self.arguments[0]
-
-        if len(self.arguments) > 1:
-            cmd += " --arch " + self.arguments[1]
 
-        srctree = path.abspath(os.environ["srctree"])
+        srctree = os.path.abspath(os.environ["srctree"])
 
-        fname = cmd
+        args = [
+            os.path.join(srctree, 'scripts/get_feat.pl'),
+            'rest',
+            '--enable-fname',
+            '--dir',
+            os.path.join(srctree, 'Documentation', self.arguments[0]),
+        ]
 
-        # extend PATH with $(srctree)/scripts
-        path_env = os.pathsep.join([
-            srctree + os.sep + "scripts",
-            os.environ["PATH"]
-        ])
-        shell_env = os.environ.copy()
-        shell_env["PATH"]    = path_env
-        shell_env["srctree"] = srctree
+        if len(self.arguments) > 1:
+            args.extend(['--arch', self.arguments[1]])
 
-        lines = self.runCmd(cmd, shell=True, cwd=cwd, env=shell_env)
+        lines = subprocess.check_output(args, cwd=os.path.dirname(doc.current_source)).decode('utf-8')
 
         line_regex = re.compile(r"^\.\. FILE (\S+)$")
 
@@ -121,30 +112,6 @@ class KernelFeat(Directive):
         nodeList = self.nestedParse(out_lines, fname)
         return nodeList
 
-    def runCmd(self, cmd, **kwargs):
-        u"""Run command ``cmd`` and return its stdout as unicode."""
-
-        try:
-            proc = subprocess.Popen(
-                cmd
-                , stdout = subprocess.PIPE
-                , stderr = subprocess.PIPE
-                , **kwargs
-            )
-            out, err = proc.communicate()
-
-            out, err = codecs.decode(out, 'utf-8'), codecs.decode(err, 'utf-8')
-
-            if proc.returncode != 0:
-                raise self.severe(
-                    u"command '%s' failed with return code %d"
-                    % (cmd, proc.returncode)
-                )
-        except OSError as exc:
-            raise self.severe(u"problems with '%s' directive: %s."
-                              % (self.name, ErrorString(exc)))
-        return out
-
     def nestedParse(self, lines, fname):
         content = ViewList()
         node    = nodes.section()