Re: [PATCH net 3/3] netconsole: propagate device name truncation in dev_name_store()

[Simon Horman <horms@kernel.org>]

From: 'Simon Horman' <horms@kernel.org>

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---
netconsole: propagate device name truncation in dev_name_store()

This commit rejects interface name writes that exceed the size of the
destination buffer to avoid silently truncating names and binding to
unintended devices.

> diff --git a/drivers/net/netconsole.c b/drivers/net/netconsole.c
> index 4bef003d9df64..3914fb90f9afd 100644
> --- a/drivers/net/netconsole.c
> +++ b/drivers/net/netconsole.c
> @@ -816,6 +816,9 @@ static ssize_t dev_name_store(struct config_item *item, const char *buf,
>  {
>  	struct netconsole_target *nt = to_target(item);
>  
> +	if (count >= IFNAMSIZ)
> +		return -ENAMETOOLONG;
> +

Does this check incorrectly reject valid maximum-length interface names when
written with a trailing newline?

Standard userspace tools like echo append a trailing newline when writing to
configfs attributes. If userspace writes a 15-character name, the count will
be exactly 16 bytes.

Since IFNAMSIZ is 16, the condition count >= IFNAMSIZ evaluates to true,
causing dev_name_store() to reject the valid input with -ENAMETOOLONG.

Prior to this patch, strscpy() safely truncated the trailing newline by
copying the 15 characters and a NUL terminator.