Audit the following candidate code to determine whether it presents a real vulnerability.
This sample may come from a noisy retrieval or transformation stage, so reason from the supplied code and context rather than assuming the label.

Repository: git.kernel.org/pub/scm/linux/kernel/git/stable/linux
Language: C
File: drivers/usb/typec/bus.c
Function: typec_altmode_attention

Call path: tcpm_handle_vdm_request (drivers/usb/typec/tcpm/tcpm.c) → typec_altmode_attention (drivers/usb/typec/bus.c) → partner->adev.ops->attention (drivers/usb/typec/bus.c)

### Primary Function

```c
int typec_altmode_attention(struct typec_altmode *adev, u32 vdo)
{
	struct altmode *partner = to_altmode(adev)->partner;
	struct typec_altmode *pdev;

	if (!partner)
		return -ENODEV;

	pdev = &partner->adev;

	if (pdev->ops && pdev->ops->attention)
		pdev->ops->attention(pdev, vdo);

	return 0;
}
```

### Cross-File Context

[altmode — struct — drivers/usb/typec/bus.h]
```c
struct altmode {
	unsigned int			id;
	struct typec_altmode		adev;
	struct typec_mux		*mux;

	enum typec_port_data		roles;

	struct attribute		*attrs[5];
	char				group_name[8];
	struct attribute_group		group;
	const struct attribute_group	*groups[2];

	struct altmode			*partner;
	struct altmode			*plug[2];
};
```

[to_altmode — macro — drivers/usb/typec/bus.h]
to_altmode → #define to_altmode(d) container_of(d, struct altmode, adev)  (drivers/usb/typec/bus.h)

[typec_altmode — struct — include/linux/usb/typec_altmode.h]
```c
struct typec_altmode {
	struct device			dev;
	u16				svid;
	int				mode;
	u32				vdo;
	unsigned int			active:1;

	char				*desc;
	const struct typec_altmode_ops	*ops;
};
```

[typec_altmode_ops — struct — include/linux/usb/typec_altmode.h]
```c
struct typec_altmode_ops {
	int (*enter)(struct typec_altmode *altmode, u32 *vdo);
	int (*exit)(struct typec_altmode *altmode);
	void (*attention)(struct typec_altmode *altmode, u32 vdo);
	int (*vdm)(struct typec_altmode *altmode, const u32 hdr,
		   const u32 *vdo, int cnt);
	int (*notify)(struct typec_altmode *altmode, unsigned long conf,
		      void *data);
	int (*activate)(struct typec_altmode *altmode, int activate);
};
```

Control flow: The function receives adev and vdo, extracts the partner altmode via container_of(adev)->partner, checks if partner is NULL and returns -ENODEV if so, otherwise derives pdev from partner->adev, checks that pdev->ops and pdev->ops->attention are non-NULL before invoking the callback, and returns 0 on success. The only error path is the early return with -ENODEV when partner is NULL.

Data flow: Input adev is transformed via to_altmode(adev) to get the enclosing struct altmode, then partner is extracted from its partner field. After the NULL check passes, pdev is derived as &partner->adev. The vdo parameter is passed through unchanged to the attention callback if it exists. The function returns -ENODEV on NULL partner or 0 on success.

Verdict: Not Vulnerable

Reviewed region:
[drivers/usb/typec/bus.c]
```c
int typec_altmode_attention(struct typec_altmode *adev, u32 vdo)
{
	struct altmode *partner = to_altmode(adev)->partner;
	struct typec_altmode *pdev;

	if (!partner)
		return -ENODEV;

	pdev = &partner->adev;

	if (pdev->ops && pdev->ops->attention)
		pdev->ops->attention(pdev, vdo);

	return 0;
}
```

Why it is not vulnerable: The code explicitly checks `if (!partner) return -ENODEV;` before any dereference of the partner pointer. This NULL guard ensures that `pdev = &partner->adev;` is only reached when partner is valid. Additionally, the callback invocation is guarded by `if (pdev->ops && pdev->ops->attention)` preventing dereference of a NULL function pointer.

Security invariants:
- partner must be non-NULL before dereferencing partner->adev — enforced by `if (!partner) return -ENODEV;`
- pdev->ops must be non-NULL before accessing pdev->ops->attention — enforced by `if (pdev->ops && pdev->ops->attention)`
- pdev->ops->attention must be non-NULL before invoking the callback — enforced by the same compound guard `if (pdev->ops && pdev->ops->attention)`

Invariant verification:
- NULL pointer check on partner before dereference: holds=true. Evidence: The statement `if (!partner) return -ENODEV;` immediately follows `struct altmode *partner = to_altmode(adev)->partner;` and precedes `pdev = &partner->adev;`, ensuring partner is validated before access.
- Callback function pointer validation before invocation: holds=true. Evidence: The condition `if (pdev->ops && pdev->ops->attention)` guards the call to `pdev->ops->attention(pdev, vdo);`, verifying both ops and the attention function pointer are non-NULL.

Residual risk notes: The validity of the adev input parameter and the correctness of container_of(adev) are assumed — a corrupted or freed adev pointer would result in undefined behavior before the partner NULL check. Additionally, the attention callback is invoked without holding any visible lock in this function; the caller (tcpm_handle_vdm_request) is responsible for appropriate synchronization. These are contextual concerns rather than vulnerabilities in this function itself.

Control flow: The function converts the input `adev` to `struct altmode` via `container_of`, extracts the `partner` pointer, and immediately checks if it is NULL (returning -ENODEV if so). If valid, it derives `pdev` from `partner->adev`, then checks whether `pdev->ops` and `pdev->ops->attention` are non-NULL before invoking the callback. The function always returns 0 on the success path.

Data flow: Input `adev` (struct typec_altmode*) is transformed via `to_altmode()` macro into `struct altmode*`. The `partner` field is extracted and validated. `pdev` is derived as `&partner->adev`. The `vdo` parameter is passed through to the `attention` callback if it exists. No modification of input data occurs.

Verdict: Not Vulnerable

Reviewed region:
[drivers/usb/typec/bus.c]
```c
int typec_altmode_attention(struct typec_altmode *adev, u32 vdo)
{
	struct altmode *partner = to_altmode(adev)->partner;
	struct typec_altmode *pdev;

	if (!partner)
		return -ENODEV;

	pdev = &partner->adev;

	if (pdev->ops && pdev->ops->attention)
		pdev->ops->attention(pdev, vdo);

	return 0;
}
```

Why it is not vulnerable: The code properly guards all pointer dereferences. The `partner` pointer is checked for NULL with `if (!partner) return -ENODEV;` before any dereference of `partner->adev`. The callback invocation `pdev->ops->attention(pdev, vdo)` is protected by the compound check `if (pdev->ops && pdev->ops->attention)`, which verifies both the ops structure and the specific function pointer are non-NULL before the call. These checks prevent NULL pointer dereference on all execution paths.

Security invariants:
- The `partner` pointer must be non-NULL before accessing `partner->adev`. Enforced by: `if (!partner) return -ENODEV;`
- The `pdev->ops` pointer must be non-NULL before accessing `pdev->ops->attention`. Enforced by: `if (pdev->ops && pdev->ops->attention)`
- The `pdev->ops->attention` function pointer must be non-NULL before invocation. Enforced by: `if (pdev->ops && pdev->ops->attention)`
- The callback receives valid parameters `(pdev, vdo)` where `pdev` is derived from a validated `partner` structure and `vdo` is the input parameter.

Invariant verification:
- NULL check on partner pointer before dereference: holds=true. Evidence: The statement `if (!partner) return -ENODEV;` immediately follows the extraction `struct altmode *partner = to_altmode(adev)->partner;` and precedes `pdev = &partner->adev;`
- NULL check on ops structure before accessing attention callback: holds=true. Evidence: The compound condition `if (pdev->ops && pdev->ops->attention)` checks `pdev->ops` first, short-circuiting if NULL, preventing dereference of a NULL ops pointer
- NULL check on attention function pointer before invocation: holds=true. Evidence: The compound condition `if (pdev->ops && pdev->ops->attention)` checks `pdev->ops->attention` before the call `pdev->ops->attention(pdev, vdo);`

Residual risk notes: The function assumes the input `adev` pointer is valid and points to a properly initialized `struct typec_altmode` embedded within a `struct altmode`. This assumption is consistent with kernel driver conventions where callers are responsible for passing valid pointers. The `container_of` macro in `to_altmode` does not validate the input pointer. Additionally, the behavior of the `attention` callback itself is not validated here, but that is outside the scope of this function's responsibility.