Re: [PATCH v3] kobject: fix out-of-bounds access in kobject_action_type()

[Greg KH <gregkh@linuxfoundation.org>]

On Sun, Sep 20, 2026 at 01:37:26PM +0800, Jiacheng Xu wrote:
> kobject_action_type() compares the input against each known action
> using strncmp() and then indexes the action string using count_first
> to check for an exact-length match.
> 
> An embedded NUL can make strncmp() return zero even when count_first
> exceeds the length of the action string. For example, the five-byte
> input "add\0X" makes the parser access kobject_actions[KOBJ_ADD][5],
> which is beyond the end of the "add" string.
> 
> Check the action string length with strlen() instead of indexing it
> with the input-derived offset. This rejects malformed action strings
> containing embedded NUL bytes with -EINVAL instead of invoking
> undefined behavior.
> 
> Fixes: 60a96a59569b ("Driver core: accept all valid action-strings in uevent-trigger")
> Signed-off-by: Jiacheng Xu <stitch@zju.edu.cn>
> Reviewed-by: Vishal Moola (Fractile) <vishal.moola@gmail.com>
> ---
> Changes in v3:
> - Document rejection of action strings containing embedded NUL bytes.
> - Correct the Fixes tag.
> - Correct the malformed-input example.
> - Add Vishal Moola's Reviewed-by tag.
> 
>  lib/kobject_uevent.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/lib/kobject_uevent.c b/lib/kobject_uevent.c
> index ddbc4d7482d2..b03562301bfe 100644
> --- a/lib/kobject_uevent.c
> +++ b/lib/kobject_uevent.c
> @@ -83,7 +83,7 @@ static int kobject_action_type(const char *buf, size_t count,
>  	for (action = 0; action < ARRAY_SIZE(kobject_actions); action++) {
>  		if (strncmp(kobject_actions[action], buf, count_first) != 0)
>  			continue;
> -		if (kobject_actions[action][count_first] != '\0')
> +		if (strlen(kobject_actions[action]) != count_first)
>  			continue;
>  		if (args)
>  			*args = args_start;
> -- 
> 2.51.0
> 

Hi,

This is the friendly patch-bot of Greg Kroah-Hartman.  You have sent him
a patch that has triggered this response.  He used to manually respond
to these common problems, but in order to save his sanity (he kept
writing the same thing over and over, yet to different people), I was
created.  Hopefully you will not take offence and will fix the problem
in your patch and resubmit it so that it can be accepted into the Linux
kernel tree.

You are receiving this message because of the following common error(s)
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thanks,

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