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 3231dd58 ("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/111676532203641247Reported-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

Documentation/admin-guide/features.rst

 .. SPDX-License-Identifier: GPL-2.0
 
-.. kernel-feat:: $srctree/Documentation/features
+.. kernel-feat:: features

Documentation/arch/arc/features.rst

 .. SPDX-License-Identifier: GPL-2.0
 
-.. kernel-feat:: $srctree/Documentation/features arc
+.. kernel-feat:: features arc

Documentation/arch/arm/features.rst

 .. SPDX-License-Identifier: GPL-2.0
 
-.. kernel-feat:: $srctree/Documentation/features arm
+.. kernel-feat:: features arm

Documentation/arch/arm64/features.rst

 .. SPDX-License-Identifier: GPL-2.0
 
-.. kernel-feat:: $srctree/Documentation/features arm64
+.. kernel-feat:: features arm64

Documentation/arch/loongarch/features.rst

 .. SPDX-License-Identifier: GPL-2.0
 
-.. kernel-feat:: $srctree/Documentation/features loongarch
+.. kernel-feat:: features loongarch

Documentation/arch/m68k/features.rst

 .. SPDX-License-Identifier: GPL-2.0
 
-.. kernel-feat:: $srctree/Documentation/features m68k
+.. kernel-feat:: features m68k

Documentation/arch/mips/features.rst

 .. SPDX-License-Identifier: GPL-2.0
 
-.. kernel-feat:: $srctree/Documentation/features mips
+.. kernel-feat:: features mips

Documentation/arch/nios2/features.rst

 .. SPDX-License-Identifier: GPL-2.0
 
-.. kernel-feat:: $srctree/Documentation/features nios2
+.. kernel-feat:: features nios2

Documentation/arch/openrisc/features.rst

 .. SPDX-License-Identifier: GPL-2.0
 
-.. kernel-feat:: $srctree/Documentation/features openrisc
+.. kernel-feat:: features openrisc

Documentation/arch/parisc/features.rst

 .. SPDX-License-Identifier: GPL-2.0
 
-.. kernel-feat:: $srctree/Documentation/features parisc
+.. kernel-feat:: features parisc

Documentation/arch/powerpc/features.rst

 .. SPDX-License-Identifier: GPL-2.0
 
-.. kernel-feat:: $srctree/Documentation/features powerpc
+.. kernel-feat:: features powerpc

Documentation/arch/riscv/features.rst

 .. SPDX-License-Identifier: GPL-2.0
 
-.. kernel-feat:: $srctree/Documentation/features riscv
+.. kernel-feat:: features riscv

Documentation/arch/s390/features.rst

 .. SPDX-License-Identifier: GPL-2.0
 
-.. kernel-feat:: $srctree/Documentation/features s390
+.. kernel-feat:: features s390

Documentation/arch/sh/features.rst

 .. SPDX-License-Identifier: GPL-2.0
 
-.. kernel-feat:: $srctree/Documentation/features sh
+.. kernel-feat:: features sh

Documentation/arch/sparc/features.rst

 .. SPDX-License-Identifier: GPL-2.0
 
-.. kernel-feat:: $srctree/Documentation/features sparc
+.. kernel-feat:: features sparc

Documentation/arch/x86/features.rst

 .. SPDX-License-Identifier: GPL-2.0
 
-.. kernel-feat:: $srctree/Documentation/features x86
+.. kernel-feat:: features x86

Documentation/arch/xtensa/features.rst

 .. SPDX-License-Identifier: GPL-2.0
 
-.. kernel-feat:: $srctree/Documentation/features xtensa
+.. kernel-feat:: features xtensa

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()

Documentation/translations/zh_CN/arch/loongarch/features.rst

@@ -5,4 +5,4 @@
 :Original: Documentation/arch/loongarch/features.rst
 :Translator: Huacai Chen <chenhuacai@loongson.cn>
 
-.. kernel-feat:: $srctree/Documentation/features loongarch
+.. kernel-feat:: features loongarch

Documentation/translations/zh_CN/arch/mips/features.rst

@@ -10,4 +10,4 @@
 
 .. _cn_features:
 
-.. kernel-feat:: $srctree/Documentation/features mips
+.. kernel-feat:: features mips

Documentation/translations/zh_TW/arch/loongarch/features.rst

@@ -5,5 +5,5 @@
 :Original: Documentation/arch/loongarch/features.rst
 :Translator: Huacai Chen <chenhuacai@loongson.cn>
 
-.. kernel-feat:: $srctree/Documentation/features loongarch
+.. kernel-feat:: features loongarch
 

Documentation/translations/zh_TW/arch/mips/features.rst

@@ -10,5 +10,5 @@
 
 .. _tw_features:
 
-.. kernel-feat:: $srctree/Documentation/features mips
+.. kernel-feat:: features mips