[PATCH net] atm: null pointer dereference when both entry and holding_time are NULL.

[PATCH net] atm: null pointer dereference when both entry and holding_time are NULL.

[pwn9uin]

From: Minjoong Kim <alswnd4123@outlook.kr>

When MPOA_cache_impos_rcvd() receives the msg, it can trigger
Null Pointer Dereference Vulnerability if both entry and
holding_time are NULL. Because there is only for the situation
where entry is NULL and holding_time exists, it can be passed
when both entry and holding_time are NULL. If these are NULL,
the entry will be passd to eg_cache_put() as parameter and
it is referenced by entry->use code in it.

Signed-off-by: Minjoong Kim <alswnd4123@outlook.kr>
Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
---
 net/atm/mpc.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/net/atm/mpc.c b/net/atm/mpc.c
index 324e3ab96bb3..7fb854ea47dc 100644
--- a/net/atm/mpc.c
+++ b/net/atm/mpc.c
@@ -1314,6 +1314,9 @@ static void MPOA_cache_impos_rcvd(struct k_message *msg,
 	holding_time = msg->content.eg_info.holding_time;
 	dprintk("(%s) entry = %p, holding_time = %u\n",
 		mpc->dev->name, entry, holding_time);
+	if (entry == NULL && !holding_time) {
+		return;
+	}
 	if (entry == NULL && holding_time) {
 		entry = mpc->eg_ops->add_entry(msg, mpc);
 		mpc->eg_ops->put(entry);
-- 
2.34.1

Re: [PATCH net] atm: null pointer dereference when both entry and holding_time are NULL.

[Simon Horman]

On Fri, Mar 14, 2025 at 12:34:04AM +0000, pwn9uin@gmail.com wrote:
> From: Minjoong Kim <alswnd4123@outlook.kr>
> 
> When MPOA_cache_impos_rcvd() receives the msg, it can trigger
> Null Pointer Dereference Vulnerability if both entry and
> holding_time are NULL. Because there is only for the situation
> where entry is NULL and holding_time exists, it can be passed
> when both entry and holding_time are NULL. If these are NULL,
> the entry will be passd to eg_cache_put() as parameter and
> it is referenced by entry->use code in it.
> 
> Signed-off-by: Minjoong Kim <alswnd4123@outlook.kr>
> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")

Hi,

I agree this is a theoretical possibility, but can it occur in practice?
Have you observed this problem? I think some analysis of that is warranted.

Also, Smatch tells me that there is a potential dereference of mpc while
NULL. Perhaps you could look at making a patch for that too?

Re: [PATCH net] atm: null pointer dereference when both entry and holding_time are NULL.

[Paolo Abeni]

On 3/14/25 1:34 AM, pwn9uin@gmail.com wrote:
> From: Minjoong Kim <alswnd4123@outlook.kr>
> 
> When MPOA_cache_impos_rcvd() receives the msg, it can trigger
> Null Pointer Dereference Vulnerability if both entry and
> holding_time are NULL. Because there is only for the situation
> where entry is NULL and holding_time exists, it can be passed
> when both entry and holding_time are NULL. If these are NULL,
> the entry will be passd to eg_cache_put() as parameter and
> it is referenced by entry->use code in it.
> 
> Signed-off-by: Minjoong Kim <alswnd4123@outlook.kr>
> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")

Please include the full splat for such UaF in the commit message

> ---
>  net/atm/mpc.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/net/atm/mpc.c b/net/atm/mpc.c
> index 324e3ab96bb3..7fb854ea47dc 100644
> --- a/net/atm/mpc.c
> +++ b/net/atm/mpc.c
> @@ -1314,6 +1314,9 @@ static void MPOA_cache_impos_rcvd(struct k_message *msg,
>  	holding_time = msg->content.eg_info.holding_time;
>  	dprintk("(%s) entry = %p, holding_time = %u\n",
>  		mpc->dev->name, entry, holding_time);
> +	if (entry == NULL && !holding_time) {
> +		return;

Brackets are unneeded here.

Thanks,

Paolo