[PATCH v2] checkpatch: Warn about 0-length and 1-element arrays

[Kees Cook]

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@xxxxxxxxxxxxx>
Cc: Dwaipayan Ray <dwaipayanray1@xxxxxxxxx>
Cc: Lukas Bulwahn <lukas.bulwahn@xxxxxxxxx>
Cc: Gustavo A. R. Silva <gustavoars@xxxxxxxxxx>
Fixed-by: Joe Perches <joe@xxxxxxxxxxx>
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20230517204530.never.151-kees@xxxxxxxxxx
---
v2: find using "end of struct" marking instead of $context_function (joe)
v1: https://lore.kernel.org/all/20230517204530.never.151-kees@xxxxxxxxxx/
---
 scripts/checkpatch.pl | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index 30b0b4fdb3bf..cfa19bfc857c 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 ($sline =~ /^[\+ ]\s*}\s*;\s*$/ &&
+		    $prevline =~ /^\+\s*(?:(?:struct|union|enum)\s+$Ident|\}|$Type)\s*$Ident\s*\[\s*(0|1)\s*\]\s*;\s*$/) {
+			if ($1 == '0') {
+				if (WARN("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/\[0\]/[]/g;
+				}
+			} else {
+				WARN("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