gh-112301: Add -Wformat=2 compiler option to NODIST #122474

nohlson · 2024-07-30T17:32:10Z

This adds -Wformat and -Wformat=2 to the CFLAGS_NODIST set of compiler flags. This is a warning flag that relates for format strings and for more information you can take a look at the OpenSSF guidance on this flag.

This does generate a few warnings in build_ubuntu and the new warning checker catches them catches them:

| {'kind': 'warning', 'locations': [{'finish': {'byte-column': 27, 'display-column': 27, 'line': 2857, 'file': '../cpython-ro-srcdir/Objects/unicodeobject.c', 'column': 27}, 'caret': {'byte-column': 21, 'display-column': 21, 'line': 2857, 'file': '../cpython-ro-srcdir/Objects/unicodeobject.c', 'column': 21}}], 'column-origin': 1, 'option': '-Wformat-nonliteral', 'children': [], 'option_url': 'https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html#index-Wformat-nonliteral', 'message': 'format not a string literal, argument types not checked'}
| {'kind': 'warning', 'locations': [{'finish': {'byte-column': 27, 'display-column': 27, 'line': 2858, 'file': '../cpython-ro-srcdir/Objects/unicodeobject.c', 'column': 27}, 'caret': {'byte-column': 21, 'display-column': 21, 'line': 2858, 'file': '../cpython-ro-srcdir/Objects/unicodeobject.c', 'column': 21}}], 'column-origin': 1, 'option': '-Wformat-nonliteral', 'children': [], 'option_url': 'https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html#index-Wformat-nonliteral', 'message': 'format not a string literal, argument types not checked'}
| {'kind': 'warning', 'locations': [{'finish': {'byte-column': 27, 'display-column': 27, 'line': 2862, 'file': '../cpython-ro-srcdir/Objects/unicodeobject.c', 'column': 27}, 'caret': {'byte-column': 21, 'display-column': 21, 'line': 2862, 'file': '../cpython-ro-srcdir/Objects/unicodeobject.c', 'column': 21}}], 'column-origin': 1, 'option': '-Wformat-nonliteral', 'children': [], 'option_url': 'https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html#index-Wformat-nonliteral', 'message': 'format not a string literal, argument types not checked'}
| {'kind': 'warning', 'locations': [{'finish': {'byte-column': 27, 'display-column': 27, 'line': 2863, 'file': '../cpython-ro-srcdir/Objects/unicodeobject.c', 'column': 27}, 'caret': {'byte-column': 21, 'display-column': 21, 'line': 2863, 'file': '../cpython-ro-srcdir/Objects/unicodeobject.c', 'column': 21}}], 'column-origin': 1, 'option': '-Wformat-nonliteral', 'children': [], 'option_url': 'https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html#index-Wformat-nonliteral', 'message': 'format not a string literal, argument types not checked'}
| {'kind': 'warning', 'locations': [{'finish': {'byte-column': 27, 'display-column': 27, 'line': 2867, 'file': '../cpython-ro-srcdir/Objects/unicodeobject.c', 'column': 27}, 'caret': {'byte-column': 21, 'display-column': 21, 'line': 2867, 'file': '../cpython-ro-srcdir/Objects/unicodeobject.c', 'column': 21}}], 'column-origin': 1, 'option': '-Wformat-nonliteral', 'children': [], 'option_url': 'https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html#index-Wformat-nonliteral', 'message': 'format not a string literal, argument types not checked'}
| {'kind': 'warning', 'locations': [{'finish': {'byte-column': 27, 'display-column': 27, 'line': 2868, 'file': '../cpython-ro-srcdir/Objects/unicodeobject.c', 'column': 27}, 'caret': {'byte-column': 21, 'display-column': 21, 'line': 2868, 'file': '../cpython-ro-srcdir/Objects/unicodeobject.c', 'column': 21}}], 'column-origin': 1, 'option': '-Wformat-nonliteral', 'children': [], 'option_url': 'https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html#index-Wformat-nonliteral', 'message': 'format not a string literal, argument types not checked'}
| {'kind': 'warning', 'locations': [{'finish': {'byte-column': 19, 'display-column': 19, 'line': 2871, 'file': '../cpython-ro-srcdir/Objects/unicodeobject.c', 'column': 19}, 'caret': {'byte-column': 17, 'display-column': 17, 'line': 2871, 'file': '../cpython-ro-srcdir/Objects/unicodeobject.c', 'column': 17}}], 'column-origin': 1, 'option': '-Wformat-nonliteral', 'children': [], 'option_url': 'https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html#index-Wformat-nonliteral', 'message': 'format not a string literal, argument types not checked'}
| {'kind': 'warning', 'locations': [{'finish': {'byte-column': 27, 'display-column': 27, 'line': 2875, 'file': '../cpython-ro-srcdir/Objects/unicodeobject.c', 'column': 27}, 'caret': {'byte-column': 21, 'display-column': 21, 'line': 2875, 'file': '../cpython-ro-srcdir/Objects/unicodeobject.c', 'column': 21}}], 'column-origin': 1, 'option': '-Wformat-nonliteral', 'children': [], 'option_url': 'https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html#index-Wformat-nonliteral', 'message': 'format not a string literal, argument types not checked'}
| {'kind': 'warning', 'locations': [{'finish': {'byte-column': 27, 'display-column': 27, 'line': 2876, 'file': '../cpython-ro-srcdir/Objects/unicodeobject.c', 'column': 27}, 'caret': {'byte-column': 21, 'display-column': 21, 'line': 2876, 'file': '../cpython-ro-srcdir/Objects/unicodeobject.c', 'column': 21}}], 'column-origin': 1, 'option': '-Wformat-nonliteral', 'children': [], 'option_url': 'https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html#index-Wformat-nonliteral', 'message': 'format not a string literal, argument types not checked'}
| {'kind': 'warning', 'locations': [{'finish': {'byte-column': 27, 'display-column': 27, 'line': 2880, 'file': '../cpython-ro-srcdir/Objects/unicodeobject.c', 'column': 27}, 'caret': {'byte-column': 21, 'display-column': 21, 'line': 2880, 'file': '../cpython-ro-srcdir/Objects/unicodeobject.c', 'column': 21}}], 'column-origin': 1, 'option': '-Wformat-nonliteral', 'children': [], 'option_url': 'https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html#index-Wformat-nonliteral', 'message': 'format not a string literal, argument types not checked'}
| {'kind': 'warning', 'locations': [{'finish': {'byte-column': 27, 'display-column': 27, 'line': 2881, 'file': '../cpython-ro-srcdir/Objects/unicodeobject.c', 'column': 27}, 'caret': {'byte-column': 21, 'display-column': 21, 'line': 2881, 'file': '../cpython-ro-srcdir/Objects/unicodeobject.c', 'column': 21}}], 'column-origin': 1, 'option': '-Wformat-nonliteral', 'children': [], 'option_url': 'https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html#index-Wformat-nonliteral', 'message': 'format not a string literal, argument types not checked'}
| {'kind': 'warning', 'locations': [{'finish': {'byte-column': 28, 'display-column': 28, 'line': 23, 'file': '../cpython-ro-srcdir/Python/getversion.c', 'column': 28}, 'caret': {'byte-column': 19, 'display-column': 19, 'line': 23, 'file': '../cpython-ro-srcdir/Python/getversion.c', 'column': 19}}], 'column-origin': 1, 'option': '-Wformat-nonliteral', 'children': [], 'option_url': 'https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html#index-Wformat-nonliteral', 'message': 'format not a string literal, argument types not checked'}

unicodeobject.c warnings look like they could be ignored since format strings for sprintf operations are pulled from a const array of const format strings, and the variable that indexes these arrays is set from constants. However if we add this file to .warningignore_ubuntu then if either of those things change maybe vulnerabilities could be introduced.

As for getversion.c it also could be ignored. I don't think there is too much of a concern in putting this in the warning ignore file.

This change should require pre-merge build bots @corona10

Attn: @hugovk

EDIT: Removed content from the issue that pertained to already merged tooling options

Issue: Consider applying flags for warnings about potential security issues #112301

bedevere-bot · 2024-07-31T01:43:14Z

🤖 New build scheduled with the buildbot fleet by @corona10 for commit 178bcc6 🤖

If you want to schedule another build, you need to add the 🔨 test-with-buildbots label again.

configure.ac

encukou · 2024-08-07T07:38:35Z

Python/getversion.c

@@ -19,8 +19,17 @@ void _Py_InitVersion(void)
 #else
    const char *buildinfo_format = "%.80s (%.80s) %.80s";
 #endif
+    // The format string is defined above and is observably safe.


Could it be switched to a #defined literal? That way it could look safe to the compiler, too.

I just pushed a change. I figure instead of going through the trouble defining a format string in the preprocessor #if/#else blocks and adding all of the diagnostic pragmas we can just put the PyOS_snprintf() with the relevant format string literals in the respective #if/#else blocks. We eliminate the root cause of the warning instead of ignore it.

encukou · 2024-08-07T11:30:14Z

Objects/unicodeobject.c

+        // is only assigned known constant values. Ignore warnings related
+        // to the format string not being a string literal.
+        #if defined(__GNUC__) || defined(__clang__)
+        #pragma GCC diagnostic push


Consider using _Py_COMP_DIAG_PUSH/_Py_COMP_DIAG_POP, and adding a macro like _Py_COMP_DIAG_IGNORE_DEPR_DECLS, to make this easier to port to other compilers.

@encukou created macro for ignoring format nonliterals and applied it to this block

encukou · 2024-09-18T08:37:26Z

I wanted to see if it's possible to avoid the warning altogether -- and had an implementation before I realized I should have probably delegated it.
Please see if #124203 makes sense to you.

nohlson added 2 commits July 30, 2024 11:42

Add -Wformat=2 compiler option to NODIST default

c5396a1

Add -Wformat to NODIST

19437ef

nohlson requested review from erlend-aasland and corona10 as code owners July 30, 2024 17:32

bedevere-app bot mentioned this pull request Jul 30, 2024

Consider applying flags for warnings about potential security issues #112301

Open

bedevere-app bot added the awaiting review label Jul 30, 2024

blurb-it bot and others added 2 commits July 30, 2024 17:34

📜🤖 Added by blurb_it.

cba84fe

Add fail on warning regression option to ubuntu builds

178bcc6

nohlson requested review from ezio-melotti and hugovk as code owners July 30, 2024 18:14

corona10 added the 🔨 test-with-buildbots Test PR w/ buildbots; report in status section label Jul 31, 2024

bedevere-bot removed the 🔨 test-with-buildbots Test PR w/ buildbots; report in status section label Jul 31, 2024

nohlson commented Jul 31, 2024

View reviewed changes

configure.ac Show resolved Hide resolved

nohlson added 2 commits August 5, 2024 16:59

Add warning ignores to code with nonliteral format strings

3bc76ca

Limit pragmas to gcc/clang

c4b8cf9

encukou reviewed Aug 7, 2024

View reviewed changes

nohlson added 5 commits August 7, 2024 13:35

Refactor version _Py_InitVersion to use format string literals

8cff32e

Merge branch 'main' into add-format-level-2

95c612c

Create pyport preprocessor macro for ignoring format nonliterals

a3b0c46

Add MSVC boilerplate macro for ignoring format nonliteral

fa52862

Add nonliteral macro

6cd1def

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gh-112301: Add -Wformat=2 compiler option to NODIST #122474

gh-112301: Add -Wformat=2 compiler option to NODIST #122474

nohlson commented Jul 30, 2024 •

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encukou commented Sep 18, 2024

gh-112301: Add -Wformat=2 compiler option to NODIST #122474

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gh-112301: Add -Wformat=2 compiler option to NODIST #122474

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nohlson commented Jul 30, 2024 •

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