linux-hardening - Re: [PATCH] checkpatch: Warn about 0-length and 1-element arrays

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Date:   Thu, 18 May 2023 12:58:49 -0700
From:   Joe Perches <joe@...ches.com>
To:     Kees Cook <keescook@...omium.org>,
        Andy Whitcroft <apw@...onical.com>
Cc:     Dwaipayan Ray <dwaipayanray1@...il.com>,
        Lukas Bulwahn <lukas.bulwahn@...il.com>,
        "Gustavo A . R . Silva" <gustavoars@...nel.org>,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH] checkpatch: Warn about 0-length and 1-element arrays

 * On Wed, 2023-05-17 at 13:45 -0700, Kees Cook wrote:
> Fake flexible arrays have been deprecated since last millennium. Proper
> C99 flexible arrays must be used throughout the kernel so
> CONFIG_FORTIFY_SOURCE and CONFIG_UBSAN_BOUNDS can provide proper array
> bounds checking.

I don't think this does what you want.

After adding this patch to checkpatch with this diff: No warning

-----------------------
diff --git a/drivers/net/netconsole.c b/drivers/net/netconsole.c
index 4f4f79532c6cf..513cb102b3b38 100644
--- a/drivers/net/netconsole.c
+++ b/drivers/net/netconsole.c
@@ -73,6 +73,11 @@ static DEFINE_SPINLOCK(target_list_lock);
 */
 static struct console netconsole_ext;
+struct foobar {
+ int a;
+ int b[1];
+};
+
 /**
 * struct netconsole_target - Represents a configured netconsole target.
 * @list: Links this target into the target_list.
-----------------------

because $context_function is DEFINE_SPINLOCK

I think you want something like:
---
 scripts/checkpatch.pl | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index b30114d637c40..778a0808c37cf 100755
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -7418,6 +7418,18 @@ sub process {
 }
 }
+ # check for array definition/declarations that should use flexible arrays instead
+ if ($sline =~ /^[\+ ]\s*}\s*;\s*$/ &&
+ $prevline =~ /^\+\s*$Type\s*$Ident\s*\[\s*(0|1)\s*\]\s*;\s*$/) {
+ if ($1 =~ '0') {
+ WARN("ZERO_LENGTH_ARRAY",
+ "Prefer C99 flexible arrays instead of zero-length arrays - see https://github.com/KSPP/linux/issues/78\n" . $hereprev);
+ } else {
+ WARN("ONE_ELEMENT_ARRAY",
+ "Prefer C99 flexible arrays instead of one-element arrays - see https://github.com/KSPP/linux/issues/79\n" . $hereprev);
+ }
+ }
+
 # nested likely/unlikely calls
 if ($line =~ /\b(?:(?:un)?likely)\s*\(\s*!?\s*(IS_ERR(?:_OR_NULL|_VALUE)?|WARN)/) {
 WARN("LIKELY_MISUSE",