Re: [PATCH] i3c: fix potential NULL dereference in send_ccc_cmd_locked

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:

Pre-existing issues:
- [Medium] This problem wasn't introduced by this patch, but the patch provides an incomplete fix for a theoretical NULL pointer dereference, leaving an identical dereference unhandled on the success path.
--

--- Patch [1]: [PATCH] i3c: fix potential NULL dereference in send_ccc_cmd_locked ---
commit e29455a4616608ee623e301c945a087b370f698f
Author: Hongling Zeng <zenghongling@kylinos.cn>

i3c: fix potential NULL dereference in send_ccc_cmd_locked

This patch restricts resetting the payload actual_len to DIRECT commands
to avoid a potential NULL pointer dereference for broadcast commands with
NULL dests and ndests > 0.

> diff --git a/drivers/i3c/master.c b/drivers/i3c/master.c
> --- a/drivers/i3c/master.c
> +++ b/drivers/i3c/master.c

[ ... ]

> @@ -1051,7 +1051,7 @@ static int i3c_master_send_ccc_cmd_locked(struct i3c_master_controller *master,
>  	for (attempt = 0; attempt < max_attempts; attempt++) {
>  		unsigned int i;
>  
> -		if (cmd->rnw)
> +		if (cmd->rnw && (cmd->id & I3C_CCC_DIRECT))
>  			for (i = 0; i < cmd->ndests; i++)
>  				cmd->dests[i].payload.actual_len = 0;
>  
>  		cmd->err = I3C_ERROR_UNKNOWN;
>  		ret = master->ops->send_ccc_cmd(master, cmd);
>  		if (!ret && cmd->err == I3C_ERROR_UNKNOWN)
>  			break;
>  	}
>  
>  	if (!ret)
>  		ret = i3c_ccc_validate_payload_len(cmd);

[Severity: Medium]
This is a pre-existing issue, but does this patch leave an identical NULL
pointer dereference unhandled on the success path?

If a broadcast command (where I3C_CCC_DIRECT is not set) with cmd->rnw true
and cmd->dests == NULL succeeds, the retry loop above is now safe. However,
execution proceeds to i3c_ccc_validate_payload_len():

drivers/i3c/master.c:i3c_ccc_validate_payload_len() {
    if (!cmd->rnw)
        return 0;

    for (i = 0; i < cmd->ndests; i++) {
        struct i3c_ccc_cmd_payload *p = &cmd->dests[i].payload;
        ...
}

Will this result in the exact same crash when evaluating
cmd->dests[i].payload?

Also, earlier in i3c_master_send_ccc_cmd_locked():

    if ((cmd->id & I3C_CCC_DIRECT) && (!cmd->dests || !cmd->ndests))
        return -EINVAL;

This early validation check only enforces cmd->dests != NULL for DIRECT
commands. Could this be updated to reject any command where cmd->dests is
NULL but cmd->ndests > 0, rather than patching individual dereferences?

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260728063045.73473-1-zenghongling@kylinos.cn?part=1

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