2024-02-24 15:17:34

by Erick Archer

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 <[email protected]>
---
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

2024-02-25 00:52:37

by Kent Overstreet

Subject: Re: [PATCH] bcachefs: Prefer struct_size over open coded arithmetic

On Sat, Feb 24, 2024 at 04:16:58PM +0100, Erick Archer wrote:
> 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:

there's no reason to break these out into multiple patches, just send me
a single patch when you're done - thanks!