linux-hardening - [PATCH v5] checkpatch: Check for 0-length and 1-element arrays

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Message-Id: <20230601160746.up.948-kees@kernel.org>
Date:   Thu,  1 Jun 2023 09:07:46 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Andy Whitcroft <apw@...onical.com>
Cc:     Kees Cook <keescook@...omium.org>,
        Dwaipayan Ray <dwaipayanray1@...il.com>,
        Lukas Bulwahn <lukas.bulwahn@...il.com>,
        Joe Perches <joe@...ches.com>,
        "Gustavo A . R . Silva" <gustavoars@...nel.org>,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: [PATCH v5] checkpatch: Check for 0-length and 1-element arrays

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.

Cc: Andy Whitcroft <apw@...onical.com>
Cc: Dwaipayan Ray <dwaipayanray1@...il.com>
Cc: Lukas Bulwahn <lukas.bulwahn@...il.com>
Fixed-by: Joe Perches <joe@...ches.com>
Signed-off-by: Kees Cook <keescook@...omium.org>
Acked-by: Gustavo A. R. Silva <gustavoars@...nel.org>
Link: https://lore.kernel.org/r/20230517204530.never.151-kees@kernel.org
---
v5: - add __packed to outer struct regex too (joe)
v4: https://lore.kernel.org/lkml/20230531004929.you.436-kees@kernel.org
v3: https://lore.kernel.org/r/20230527020929.give.261-kees@kernel.org
v2: https://lore.kernel.org/lkml/20230526173921.gonna.349-kees@kernel.org
v1: https://lore.kernel.org/lkml/20230517204530.never.151-kees@kernel.org
---
 scripts/checkpatch.pl | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index 30b0b4fdb3bf..7bfa4d39d17f 100755
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -7430,6 +7430,16 @@ sub process {
 			}
 		}
 
+# check for array definition/declarations that should use flexible arrays instead
+		if ($sline =~ /^[\+ ]\s*\}(?:\s*__packed)?\s*;\s*$/ &&
+		    $prevline =~ /^\+\s*(?:\}(?:\s*__packed\s*)?|$Type)\s*$Ident\s*\[\s*(0|1)\s*\]\s*;\s*$/) {
+			if (ERROR("FLEXIBLE_ARRAY",
+				  "Use C99 flexible arrays - see https://docs.kernel.org/process/deprecated.html#zero-length-and-one-element-arrays\n" . $hereprev) &&
+			    $1 == '0' && $fix) {
+				$fixed[$fixlinenr - 1] =~ s/\[\s*0\s*\]/[]/;
+			}
+		}
+
 # nested likely/unlikely calls
 		if ($line =~ /\b(?:(?:un)?likely)\s*\(\s*!?\s*(IS_ERR(?:_OR_NULL|_VALUE)?|WARN)/) {
 			WARN("LIKELY_MISUSE",
-- 
2.34.1