[PATCH v3] checkpatch: Check for 0-length and 1-element arrays

[Kees Cook <keescook@chromium.org>]

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@canonical.com>
Cc: Dwaipayan Ray <dwaipayanray1@gmail.com>
Cc: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Cc: Gustavo A. R. Silva <gustavoars@kernel.org>
Fixed-by: Joe Perches <joe@perches.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20230517204530.never.151-kees@kernel.org
---
v3:
 - Switch to ERROR from WARN
 - drop needless struct/union/enum prefix (joe)
 - fix $fixed regs (joe)
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 | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index 30b0b4fdb3bf..5307c85b93d8 100755
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -7430,6 +7430,21 @@ 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') {
+				if (ERROR("ZERO_LENGTH_ARRAY",
+					  "Use C99 flexible arrays instead of zero-length arrays - see https://github.com/KSPP/linux/issues/78\n" . $hereprev) &&
+				    $fix) {
+					$fixed[$fixlinenr - 1] =~ s/\[\s*0\s*\]/[]/;
+				}
+			} else {
+				ERROR("ONE_ELEMENT_ARRAY",
+				      "Use 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",
-- 
2.34.1