linux-kernel - [PATCH v4] checkpatch: Check for missing sentinels in ID arrays

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Message-ID: <20250702235245.1007351-1-briannorris@chromium.org>
Date: Wed,  2 Jul 2025 16:52:00 -0700
From: Brian Norris <briannorris@...omium.org>
To: Andy Whitcroft <apw@...onical.com>,
	Joe Perches <joe@...ches.com>
Cc: linux-kernel@...r.kernel.org,
	Brian Norris <briannorris@...omium.org>,
	Dwaipayan Ray <dwaipayanray1@...il.com>,
	Lukas Bulwahn <lukas.bulwahn@...il.com>
Subject: [PATCH v4] checkpatch: Check for missing sentinels in ID arrays

All of the ID tables based on <linux/mod_devicetable.h> (of_device_id,
pci_device_id, ...) require their arrays to end in an empty sentinel
value. That's usually spelled with an empty initializer entry (e.g.,
"{}"), but also sometimes with explicit 0 entries, field initializers
(e.g., '.id = ""'), or even a macro entry (like PCMCIA_DEVICE_NULL).

Without a sentinel, device-matching code may read out of bounds.

I've found a number of such bugs in driver reviews, and we even
occasionally commit one to the tree. See commit 5751eee5c620 ("i2c:
nomadik: Add missing sentinel to match table") for example.

Teach checkpatch to find these ID tables, and complain if it looks like
there wasn't a sentinel value.

Test output:

  $ git format-patch -1 a0d15cc47f29be6d --stdout | scripts/checkpatch.pl -
  ERROR: missing sentinel in ID array
  #57: FILE: drivers/i2c/busses/i2c-nomadik.c:1073:
  +static const struct of_device_id nmk_i2c_eyeq_match_table[] = {
   	{
   		.compatible = "XXXXXXXXXXXXXXXXXX",
   		.data = (void *)(NMK_I2C_EYEQ_FLAG_32B_BUS | NMK_I2C_EYEQ_FLAG_IS_EYEQ5),
   	},
   };

  total: 1 errors, 0 warnings, 66 lines checked

  NOTE: For some of the reported defects, checkpatch may be able to
        mechanically convert to the typical style using --fix or --fix-inplace.

  "[PATCH] i2c: nomadik: switch from of_device_is_compatible() to" has style problems, please review.

  NOTE: If any of the errors are false positives, please report
        them to the maintainer, see CHECKPATCH in MAINTAINERS.

When run across the entire tree (scripts/checkpatch.pl -q --types
MISSING_SENTINEL -f ...), false positives exist:

* where macros are used that hide the table from analysis
  (e.g., drivers/gpu/drm/radeon/radeon_drv.c / radeon_PCI_IDS).
  There are fewer than 5 of these.

* where such tables are processed correctly via ARRAY_SIZE() (fewer than
  5 instances). This is by far not the typical usage of *_device_id
  arrays.

* some odd parsing artifacts, where ctx_statement_block() seems to quit
  in the middle of a block due to #if/#else/#endif.

Also, not every "struct *_device_id" is in fact a sentinel-requiring
structure, but even with such types, false positives are very rare.

Signed-off-by: Brian Norris <briannorris@...omium.org>
---
 v1: https://lore.kernel.org/all/20241218232716.3624531-1-briannorris@chromium.org/

Changes in v4:
 * switch to a fuzzy regex instead of a fixed list of <foo>_device_id
   types
 * allow for variations on whitespace
 * add NULL sentinel

Changes in v3:
 * actually CC LKML this time (sorry, I accidentally sent v2 directly to
   maintainers)
 * no other change

Changes in v2:
 * add a few ID types I missed (i2c, i3c, ieee1394); this time I parsed:
     grep 'struct .*_device_id {' include/linux/mod_devicetable.h
 * account for some alternative sentinels (e.g.,
   ISAPNP_DEVICE_SINGLE_END)

 scripts/checkpatch.pl | 28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)

diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index 664f7b7a622c..a241cea2855e 100755
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -685,6 +685,9 @@ our $tracing_logging_tags = qr{(?xi:
 	[\.\!:\s]*
 )};
 
+# Device ID types like found in include/linux/mod_devicetable.h.
+our $dev_id_types = qr{\b[a-z]\w*_device_id\b};
+
 sub edit_distance_min {
 	my (@arr) = @_;
 	my $len = scalar @arr;
@@ -7678,6 +7681,31 @@ sub process {
 			WARN("DUPLICATED_SYSCTL_CONST",
 				"duplicated sysctl range checking value '$1', consider using the shared one in include/linux/sysctl.h\n" . $herecurr);
 		}
+
+# Check that *_device_id tables have sentinel entries.
+		if (defined $stat && $line =~ /struct\s+$dev_id_types\s+\w+\s*\[\s*\]\s*=\s*\{/) {
+			my $stripped = $stat;
+
+			# Strip diff line prefixes.
+			$stripped =~ s/(^|\n)./$1/g;
+			# Line continuations.
+			$stripped =~ s/\\\n/\n/g;
+			# Strip whitespace, empty strings, zeroes, and commas.
+			$stripped =~ s/""//g;
+			$stripped =~ s/0x0//g;
+			$stripped =~ s/[\s$;,0]//g;
+			# Strip field assignments.
+			$stripped =~ s/\.$Ident=//g;
+
+			if (!(substr($stripped, -4) eq "{}};" ||
+			      substr($stripped, -6) eq "{{}}};" ||
+			      $stripped =~ /ISAPNP_DEVICE_SINGLE_END}};$/ ||
+			      $stripped =~ /ISAPNP_CARD_END}};$/ ||
+			      $stripped =~ /NULL};$/ ||
+			      $stripped =~ /PCMCIA_DEVICE_NULL};$/)) {
+				ERROR("MISSING_SENTINEL", "missing sentinel in ID array\n" . "$here\n$stat\n");
+			}
+		}
 	}
 
 	# If we have no input at all, then there is nothing to report on
-- 
2.50.0.727.gbf7dc18ff4-goog