linux-hardening - [PATCH] bcachefs: Prefer struct

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Date: Sat, 24 Feb 2024 16:16:58 +0100
From: Erick Archer <erick.archer@....com>
To: Kent Overstreet <kent.overstreet@...ux.dev>,
	Brian Foster <bfoster@...hat.com>,
	"Gustavo A. R. Silva" <gustavoars@...nel.org>,
	Kees Cook <keescook@...omium.org>
Cc: Erick Archer <erick.archer@....com>,
	linux-bcachefs@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	linux-hardening@...r.kernel.org
Subject: [PATCH] bcachefs: Prefer struct_size over open coded arithmetic

This is an effort to get rid of all multiplications from allocation
functions in order to prevent integer overflows [1][2].

As the "t" variable is a pointer to "struct journal_seq_blacklist_table"
and this structure ends in a flexible array:

struct journal_seq_blacklist_table {
	[...]
	struct journal_seq_blacklist_table_entry {
		u64		start;
		u64		end;
		bool		dirty;
	}			entries[];
};

the preferred way in the kernel is to use the struct_size() helper to
do the arithmetic instead of the argument "size + size * count" in the
kzalloc() function.

This way, the code is more readable and safer.

Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#open-coded-arithmetic-in-allocator-arguments [1]
Link: https://github.com/KSPP/linux/issues/160 [2]
Signed-off-by: Erick Archer <erick.archer@....com>
---
 fs/bcachefs/journal_seq_blacklist.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/fs/bcachefs/journal_seq_blacklist.c b/fs/bcachefs/journal_seq_blacklist.c
index 024c9b1b323f..2c2490aa15fe 100644
--- a/fs/bcachefs/journal_seq_blacklist.c
+++ b/fs/bcachefs/journal_seq_blacklist.c
@@ -165,8 +165,7 @@ int bch2_blacklist_table_initialize(struct bch_fs *c)
 	if (!bl)
 		return 0;

-	t = kzalloc(sizeof(*t) + sizeof(t->entries[0]) * nr,
-		    GFP_KERNEL);
+	t = kzalloc(struct_size(t, entries, nr), GFP_KERNEL);
 	if (!t)
 		return -BCH_ERR_ENOMEM_blacklist_table_init;

--
2.25.1