As noted in the "Deprecated Interfaces, Language Features, Attributes, and Conventions" documentation [1], size calculations (especially multiplication) should not be performed in memory allocator (or similar) function arguments due to the risk of them overflowing. This could lead to values wrapping around and a smaller allocation being made than the caller was expecting. Using those allocations could lead to linear overflows of heap memory and other misbehaviors. In this case these are not actually dynamic sizes: all the operands involved in the calculation are constant values. However it is better to refactor them anyway, just to keep the open-coded math idiom out of code. So, use the struct_size() helper to do the arithmetic instead of the argument "size + count * size" in the kzalloc() functions. This code was detected with the help of Coccinelle and audited and fixed manually. [1] https://www.kernel.org/doc/html/latest/process/deprecated.html#open-coded-arithmetic-in-allocator-arguments Signed-off-by: Len Baker <len.baker@xxxxxxx> --- Changelog v1 -> v2 - Rebase against v5.15-rc2 - Refactor another instance in the same file (Gustavo A. R. Silva). - Update the commit changelog to inform that this code was detected using a Coccinelle script (Gustavo A. R. Silva). fs/fs-writeback.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c index 81ec192ce067..5eb0ada7468c 100644 --- a/fs/fs-writeback.c +++ b/fs/fs-writeback.c @@ -566,7 +566,7 @@ static void inode_switch_wbs(struct inode *inode, int new_wb_id) if (atomic_read(&isw_nr_in_flight) > WB_FRN_MAX_IN_FLIGHT) return; - isw = kzalloc(sizeof(*isw) + 2 * sizeof(struct inode *), GFP_ATOMIC); + isw = kzalloc(struct_size(isw, inodes, 2), GFP_ATOMIC); if (!isw) return; @@ -624,8 +624,8 @@ bool cleanup_offline_cgwb(struct bdi_writeback *wb) int nr; bool restart = false; - isw = kzalloc(sizeof(*isw) + WB_MAX_INODES_PER_ISW * - sizeof(struct inode *), GFP_KERNEL); + isw = kzalloc(struct_size(isw, inodes, WB_MAX_INODES_PER_ISW), + GFP_KERNEL); if (!isw) return restart; -- 2.25.1
