linux-hardening - [PATCH] dm integrity: Use struct_group() to zero struct journal

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Date:   Thu, 18 Nov 2021 12:36:40 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Alasdair Kergon <agk@...hat.com>
Cc:     Kees Cook <keescook@...omium.org>,
        Mike Snitzer <snitzer@...hat.com>,
        linux-kernel@...r.kernel.org, dm-devel@...hat.com,
        linux-hardening@...r.kernel.org
Subject: [PATCH] dm integrity: Use struct_group() to zero struct journal_sector

In preparation for FORTIFY_SOURCE performing compile-time and run-time
field bounds checking for memset(), avoid intentionally writing across
neighboring fields.

Add struct_group() to mark region of struct journal_sector that should be
initialized to zero.

Signed-off-by: Kees Cook <keescook@...omium.org>
---
 drivers/md/dm-integrity.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/drivers/md/dm-integrity.c b/drivers/md/dm-integrity.c
index 6319deccbe09..163c94ca4e5c 100644
--- a/drivers/md/dm-integrity.c
+++ b/drivers/md/dm-integrity.c
@@ -121,8 +121,10 @@ struct journal_entry {
 #define JOURNAL_MAC_SIZE		(JOURNAL_MAC_PER_SECTOR * JOURNAL_BLOCK_SECTORS)
 
 struct journal_sector {
-	__u8 entries[JOURNAL_SECTOR_DATA - JOURNAL_MAC_PER_SECTOR];
-	__u8 mac[JOURNAL_MAC_PER_SECTOR];
+	struct_group(sectors,
+		__u8 entries[JOURNAL_SECTOR_DATA - JOURNAL_MAC_PER_SECTOR];
+		__u8 mac[JOURNAL_MAC_PER_SECTOR];
+	);
 	commit_id_t commit_id;
 };
 
@@ -2870,7 +2872,8 @@ static void init_journal(struct dm_integrity_c *ic, unsigned start_section,
 		wraparound_section(ic, &i);
 		for (j = 0; j < ic->journal_section_sectors; j++) {
 			struct journal_sector *js = access_journal(ic, i, j);
-			memset(&js->entries, 0, JOURNAL_SECTOR_DATA);
+			BUILD_BUG_ON(sizeof(js->sectors) != JOURNAL_SECTOR_DATA);
+			memset(&js->sectors, 0, sizeof(js->sectors));
 			js->commit_id = dm_integrity_commit_id(ic, i, j, commit_seq);
 		}
 		for (j = 0; j < ic->journal_section_entries; j++) {
-- 
2.30.2