[apparmor] [PATCH] apparmor: Fix wrong dentry in RENAME_EXCHANGE uid check

[Georgia Garcia]

Hello,

On Mon, 2026-04-13 at 17:03 +0800, Dudu Lu wrote:
> In apparmor_path_rename(), when handling RENAME_EXCHANGE, the
> cond_exchange structure is supposed to carry the attributes of the
> *new* dentry (since it is used to authorize moving new_dentry to the
> old location). However, line 412 reads:
> 
>     vfsuid = i_uid_into_vfsuid(idmap, d_backing_inode(old_dentry));
> 
> This fetches the uid of old_dentry instead of new_dentry. As a result,
> the RENAME_EXCHANGE permission check uses the wrong file owner, which
> can allow a rename that should be denied (if old_dentry's owner has
> more privileges) or deny one that should be allowed.
> 
> Note that cond_exchange.mode on the line above correctly uses
> new_dentry. Only the uid lookup is wrong.
> 
> Fix by changing old_dentry to new_dentry in the i_uid_into_vfsuid call.
> 

This looks correct to me, but could you add a Fixes tag?

Fixes: 5e26a01e56fd ("apparmor: use type safe idmapping helpers")

Thank you,
Georgia

> Signed-off-by: Dudu Lu <phx0fer at gmail.com>
> ---
>  security/apparmor/lsm.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/security/apparmor/lsm.c b/security/apparmor/lsm.c
> index c1d42fc72fdb..e8de919fbea6 100644
> --- a/security/apparmor/lsm.c
> +++ b/security/apparmor/lsm.c
> @@ -409,7 +409,7 @@ static int apparmor_path_rename(const struct path *old_dir, struct dentry *old_d
>  			struct path_cond cond_exchange = {
>  				.mode = d_backing_inode(new_dentry)->i_mode,
>  			};
> -			vfsuid = i_uid_into_vfsuid(idmap, d_backing_inode(old_dentry));
> +			vfsuid = i_uid_into_vfsuid(idmap, d_backing_inode(new_dentry));
>  			cond_exchange.uid = vfsuid_into_kuid(vfsuid);
>  
>  			error = aa_path_perm(OP_RENAME_SRC, current_cred(),