Re: [PATCH 2/2] [v2] net/mlx5: fix possible stack overflows

Simon Horman
2024-02-20T08:06:30Z

On Mon, Feb 19, 2024 at 11:04:56AM +0100, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@arndb.de>
>
> A couple of debug functions use a 512 byte temporary buffer and call another
> function that has another buffer of the same size, which in turn exceeds the
> usual warning limit for excessive stack usage:
>
> drivers/net/ethernet/mellanox/mlx5/core/steering/dr_dbg.c:1073:1: error: stack frame size (1448) exceeds limit (1024) in 'dr_dump_start' [-Werror,-Wframe-larger-than]
> dr_dump_start(struct seq_file *file, loff_t *pos)
> drivers/net/ethernet/mellanox/mlx5/core/steering/dr_dbg.c:1009:1: error: stack frame size (1120) exceeds limit (1024) in 'dr_dump_domain' [-Werror,-Wframe-larger-than]
> dr_dump_domain(struct seq_file *file, struct mlx5dr_domain *dmn)
> drivers/net/ethernet/mellanox/mlx5/core/steering/dr_dbg.c:705:1: error: stack frame size (1104) exceeds limit (1024) in 'dr_dump_matcher_rx_tx' [-Werror,-Wframe-larger-than]
> dr_dump_matcher_rx_tx(struct seq_file *file, bool is_rx,
>
> Rework these so that each of the various code paths only ever has one of
> these buffers in it, and exactly the functions that declare one have
> the 'noinline_for_stack' annotation that prevents them from all being
> inlined into the same caller.
>
> Fixes: 917d1e799ddf ("net/mlx5: DR, Change SWS usage to debug fs seq_file interface")
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
> [v2] no changes, just based on patch 1/2 but can still be applied independently
> ---
> .../mellanox/mlx5/core/steering/dr_dbg.c | 82 +++++++++----------
> 1 file changed, 41 insertions(+), 41 deletions(-)
>
> diff --git a/drivers/net/ethernet/mellanox/mlx5/core/steering/dr_dbg.c b/drivers/net/ethernet/mellanox/mlx5/core/steering/dr_dbg.c
> index be7a8481d7d2..eae04f66b8f4 100644
> --- a/drivers/net/ethernet/mellanox/mlx5/core/steering/dr_dbg.c
> +++ b/drivers/net/ethernet/mellanox/mlx5/core/steering/dr_dbg.c
> @@ -205,12 +205,11 @@ dr_dump_hex_print(char hex[DR_HEX_SIZE], char *src, u32 size)
> }
>
> static int
> -dr_dump_rule_action_mem(struct seq_file *file, const u64 rule_id,
> +dr_dump_rule_action_mem(struct seq_file *file, char *buff, const u64 rule_id,
> struct mlx5dr_rule_action_member *action_mem)
> {
> struct mlx5dr_action *action = action_mem->action;
> const u64 action_id = DR_DBG_PTR_TO_ID(action);
> - char buff[MLX5DR_DEBUG_DUMP_BUFF_LENGTH];
> u64 hit_tbl_ptr, miss_tbl_ptr;
> u32 hit_tbl_id, miss_tbl_id;
> int ret;

Hi Arnd,

With patch 1/2 in place this code goes on as:

switch (action->action_type) {
case DR_ACTION_TYP_DROP:
memset(buff, 0, sizeof(buff));

buff is now a char * rather than an array of char.
siceof(buff) doesn't seem right here anymore.

Flagged by Coccinelle.