[PATCH] afs: Fix potential null pointer dereference in afs_put_server

[Jeffrey E Altman]

On 9/23/2025 3:51 AM, Zhen Ni wrote:
> afs_put_server() accessed server->debug_id before the NULL check, which
> could lead to a null pointer dereference. Move the debug_id assignment,
> ensuring we never dereference a NULL server pointer.
>
> Fixes: 2757a4dc1849 ("afs: Fix access after dec in put functions")
> Cc: stable at vger.kernel.org
> Signed-off-by: Zhen Ni <zhen.ni at easystack.cn>
> ---
>   fs/afs/server.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/fs/afs/server.c b/fs/afs/server.c
> index a97562f831eb..c4428ebddb1d 100644
> --- a/fs/afs/server.c
> +++ b/fs/afs/server.c
> @@ -331,13 +331,14 @@ struct afs_server *afs_use_server(struct afs_server *server, bool activate,
>   void afs_put_server(struct afs_net *net, struct afs_server *server,
>   		    enum afs_server_trace reason)
>   {
> -	unsigned int a, debug_id = server->debug_id;
> +	unsigned int a, debug_id;
>   	bool zero;
>   	int r;
>   
>   	if (!server)
>   		return;
>   
> +	debug_id = server->debug_id;
>   	a = atomic_read(&server->active);
>   	zero = __refcount_dec_and_test(&server->ref, &r);
>   	trace_afs_server(debug_id, r - 1, a, reason);

Looks good.

Reviewed-by: Jeffrey Altman <jaltman at auristor.com>


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