[PATCH v2] bcachefs: Prefer struct_size over open coded arithmetic

[Erick Archer]

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

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

struct promote_op {
	[...]
	struct bio_vec bi_inline_vecs[];
};

and the "t" variable is a pointer to "struct journal_seq_blacklist_table"
and this structure also 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() functions.

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@xxxxxxx>
---
Changes in v2:
- Merge the two patches in one single patch (Kent Overstreet).

Previous versions:
v1 -> https://lore.kernel.org/linux-hardening/20240224145924.7468-1-erick.archer@xxxxxxx/
v1 -> https://lore.kernel.org/linux-hardening/20240224151658.8272-1-erick.archer@xxxxxxx/
---
 fs/bcachefs/io_read.c               | 2 +-
 fs/bcachefs/journal_seq_blacklist.c | 3 +--
 2 files changed, 2 insertions(+), 3 deletions(-)

diff --git a/fs/bcachefs/io_read.c b/fs/bcachefs/io_read.c
index dce136cd2271..01beab55c6b3 100644
--- a/fs/bcachefs/io_read.c
+++ b/fs/bcachefs/io_read.c
@@ -174,7 +174,7 @@ static struct promote_op *__promote_alloc(struct btree_trans *trans,
 	if (!bch2_write_ref_tryget(c, BCH_WRITE_REF_promote))
 		return ERR_PTR(-BCH_ERR_nopromote_no_writes);

-	op = kzalloc(sizeof(*op) + sizeof(struct bio_vec) * pages, GFP_KERNEL);
+	op = kzalloc(struct_size(op, bi_inline_vecs, pages), GFP_KERNEL);
 	if (!op) {
 		ret = -BCH_ERR_nopromote_enomem;
 		goto err;
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