ath11k: mhi: fix potential memory leak in ath11k_mhi_register()

mhi_alloc_controller() allocates a memory space for mhi_ctrl. When some
errors occur, mhi_ctrl should be freed by mhi_free_controller(). But
when ath11k_mhi_read_addr_from_dt() fails, the function returns without
calling mhi_free_controller(), which will lead to a memory leak.

We can fix it by calling mhi_free_controller() when
ath11k_mhi_read_addr_from_dt() fails.

Signed-off-by: Jianglei Nie <niejianglei2021@163.com>
---
 drivers/net/wireless/ath/ath11k/mhi.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

On 5/26/2022 3:02 AM, Jianglei Nie wrote:
> mhi_alloc_controller() allocates a memory space for mhi_ctrl. When some
> errors occur, mhi_ctrl should be freed by mhi_free_controller(). But
> when ath11k_mhi_read_addr_from_dt() fails, the function returns without
> calling mhi_free_controller(), which will lead to a memory leak.
> 
> We can fix it by calling mhi_free_controller() when
> ath11k_mhi_read_addr_from_dt() fails.
> 
> Signed-off-by: Jianglei Nie <niejianglei2021@163.com>

Reviewed-by: Jeff Johnson <quic_jjohnson@quicinc.com>

> ---
>   drivers/net/wireless/ath/ath11k/mhi.c | 4 +++-
>   1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/net/wireless/ath/ath11k/mhi.c b/drivers/net/wireless/ath/ath11k/mhi.c
> index fc3524e83e52..3318c7c2b32b 100644
> --- a/drivers/net/wireless/ath/ath11k/mhi.c
> +++ b/drivers/net/wireless/ath/ath11k/mhi.c
> @@ -376,8 +376,10 @@ int ath11k_mhi_register(struct ath11k_pci *ab_pci)
>   
>   	if (test_bit(ATH11K_FLAG_FIXED_MEM_RGN, &ab->dev_flags)) {
>   		ret = ath11k_mhi_read_addr_from_dt(mhi_ctrl);
> -		if (ret < 0)
> +		if (ret < 0) {
> +			mhi_free_controller(mhi_ctrl);
>   			return ret;
> +		}
>   	} else {
>   		mhi_ctrl->iova_start = 0;
>   		mhi_ctrl->iova_stop = 0xFFFFFFFF;

This patch looks good to me. However there is an additional issue that 
IMO should be addressed in this function with a separate patch.

Just after mhi_ctrl is allocated the pointer is saved:
	ab_pci->mhi_ctrl = mhi_ctrl;

When there is an error, mhi_ctrl is freed, but ab_pci->mhi_ctrl still 
has a dangling pointer to the freed memory. This has the potential to 
result in a subsequent use-after-free or double-free error.

So IMO we should do one of two things (I haven't looked at the code in 
detail to determine which is better):

1) don't set ab_pci->mhi_ctrl = mhi_ctrl until the end of the function 
after success from mhi_register_controller(). This requires that none of 
the functions called between the current assignment point and the 
proposed assignment point dereference ab_pci->mhi_ctrl

2) set ab_pci->mhi_ctrl = NULL in all of the places where we call 
mhi_free_controller()

2a) have a central error exit label and have all of the error conditions 
goto that label where there is a central code:
	mhi_free_controller(mhi_ctrl);
	ab_pci->mhi_ctrl = NULL;
	return ret;