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.

[joe@perches.com: various suggestions]
Link: https://lkml.kernel.org/r/20230601160746.up.948-kees@kernel.org
Link: https://lore.kernel.org/r/20230517204530.never.151-kees@kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>
Acked-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Acked-by: Joe Perches <joe@perches.com>
Cc: Andy Whitcroft <apw@canonical.com>
Cc: Dwaipayan Ray <dwaipayanray1@gmail.com>
Cc: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index b30114d..1584794 100755 (executable)
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -7418,6 +7418,16 @@ 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",