Re: [PATCH v2] wifi: mt76: Fix strscpy buffer overflow in mt76_connac2_load_patch

[Matthew Schwartz <matthew.schwartz@linux.dev>]

> On Dec 5, 2025, at 8:12 AM, Mikhail Gavrilov <mikhail.v.gavrilov@gmail.com> wrote:
> 
> Commit f804a5895eba ("wifi: mt76: Strip whitespace from build ddate") introduced
> a kernel panic/WARN on systems using MediaTek MT7921e (and potentially others
> using mt76_connac_lib) due to an incorrect buffer size calculation.
> 
> The error logged is:
> "strnlen: detected buffer overflow: 17 byte read of buffer size 16"
> 
> This occurs because the field 'hdr->build_date' is a fixed-size array of 16 bytes.
> The patch allocated a 17-byte local buffer 'build_date' but used 'sizeof(build_date)'
> (17) as the read limit for strscpy, causing Fortify Source to correctly detect
> an attempt to read 17 bytes from the 16-byte source field.
> 
> To fix this, replace strscpy with memcpy, which is appropriate for raw data
> copying, and explicitly use the size of the source field (sizeof(hdr->build_date) = 16)
> to limit the read, followed by manual null termination.
> 
> Fixes: f804a5895eba ("wifi: mt76: Strip whitespace from build ddate")
> Signed-off-by: Mikhail Gavrilov <mikhail.v.gavrilov@gmail.com>

Ran into this kernel panic while booting into 6.19-rc1 on my handheld, this patch fixed it.

Tested-by: Matthew Schwartz <matthew.schwartz@linux.dev>

> ---
> drivers/net/wireless/mediatek/mt76/mt76_connac_mcu.c | 7 +++++--
> 1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/wireless/mediatek/mt76/mt76_connac_mcu.c b/drivers/net/wireless/mediatek/mt76/mt76_connac_mcu.c
> index ea99167765b0..d2c4c65ec464 100644
> --- a/drivers/net/wireless/mediatek/mt76/mt76_connac_mcu.c
> +++ b/drivers/net/wireless/mediatek/mt76/mt76_connac_mcu.c
> @@ -3125,8 +3125,11 @@ int mt76_connac2_load_patch(struct mt76_dev *dev, const char *fw_name)
> }
> 
> hdr = (const void *)fw->data;
> - strscpy(build_date, hdr->build_date, sizeof(build_date));
> - build_date[16] = '\0';
> + /* hdr->build_date is 16 bytes. Copy exactly 16 bytes to the 17-byte buffer,
> + * and then add the null terminator at index 16.
> + */
> + memcpy(build_date, hdr->build_date, sizeof(hdr->build_date));
> + build_date[sizeof(hdr->build_date)] = '\0';
> strim(build_date);
> dev_info(dev->dev, "HW/SW Version: 0x%x, Build Time: %.16s\n",
> be32_to_cpu(hdr->hw_sw_ver), build_date);
> -- 
> 2.52.0
> 
>