[v3] ceph: quota: Fix invalid pointer access if get_quota_realm return ERR_PTR

This issue is reported by smatch that get_quota_realm() might return
ERR_PTR but we did not handle it. It's not a immediate bug, while we
still should address it to avoid potential bugs if get_quota_realm()
is changed to return other ERR_PTR in future.

Set ceph_snap_realm's pointer in get_quota_realm()'s to address this
issue, the pointer would be set to NULL if get_quota_realm() failed
to get struct ceph_snap_realm, so no ERR_PTR would happen any more.

Signed-off-by: Wenchao Hao <haowenchao2@huawei.com>
---
V3:
 - Remove redundant variable initialization in ceph_quota_is_same_realm

V2:
 - Fix all potential invalid pointer access caused by get_quota_realm
 - Update commit comment and point it's not a immediate bug

 fs/ceph/quota.c | 39 ++++++++++++++++++++++-----------------
 1 file changed, 22 insertions(+), 17 deletions(-)

On 11/23/23 09:53, Wenchao Hao wrote:
> This issue is reported by smatch that get_quota_realm() might return
> ERR_PTR but we did not handle it. It's not a immediate bug, while we
> still should address it to avoid potential bugs if get_quota_realm()
> is changed to return other ERR_PTR in future.
>
> Set ceph_snap_realm's pointer in get_quota_realm()'s to address this
> issue, the pointer would be set to NULL if get_quota_realm() failed
> to get struct ceph_snap_realm, so no ERR_PTR would happen any more.
>
> Signed-off-by: Wenchao Hao <haowenchao2@huawei.com>
> ---
> V3:
>   - Remove redundant variable initialization in ceph_quota_is_same_realm
>
> V2:
>   - Fix all potential invalid pointer access caused by get_quota_realm
>   - Update commit comment and point it's not a immediate bug
>
>   fs/ceph/quota.c | 39 ++++++++++++++++++++++-----------------
>   1 file changed, 22 insertions(+), 17 deletions(-)
>
> diff --git a/fs/ceph/quota.c b/fs/ceph/quota.c
> index 9d36c3532de1..b25906a5bfbb 100644
> --- a/fs/ceph/quota.c
> +++ b/fs/ceph/quota.c
> @@ -197,10 +197,10 @@ void ceph_cleanup_quotarealms_inodes(struct ceph_mds_client *mdsc)
>   }
>   
>   /*
> - * This function walks through the snaprealm for an inode and returns the
> - * ceph_snap_realm for the first snaprealm that has quotas set (max_files,
> + * This function walks through the snaprealm for an inode and set the
> + * realmp with the first snaprealm that has quotas set (max_files,
>    * max_bytes, or any, depending on the 'which_quota' argument).  If the root is
> - * reached, return the root ceph_snap_realm instead.
> + * reached, set the realmp with the root ceph_snap_realm instead.
>    *
>    * Note that the caller is responsible for calling ceph_put_snap_realm() on the
>    * returned realm.
> @@ -211,10 +211,9 @@ void ceph_cleanup_quotarealms_inodes(struct ceph_mds_client *mdsc)
>    * this function will return -EAGAIN; otherwise, the snaprealms walk-through
>    * will be restarted.
>    */
> -static struct ceph_snap_realm *get_quota_realm(struct ceph_mds_client *mdsc,
> -					       struct inode *inode,
> -					       enum quota_get_realm which_quota,
> -					       bool retry)
> +static int get_quota_realm(struct ceph_mds_client *mdsc, struct inode *inode,
> +			   enum quota_get_realm which_quota,
> +			   struct ceph_snap_realm **realmp, bool retry)
>   {
>   	struct ceph_client *cl = mdsc->fsc->client;
>   	struct ceph_inode_info *ci = NULL;
> @@ -222,8 +221,10 @@ static struct ceph_snap_realm *get_quota_realm(struct ceph_mds_client *mdsc,
>   	struct inode *in;
>   	bool has_quota;
>   
> +	if (realmp)
> +		*realmp = NULL;
>   	if (ceph_snap(inode) != CEPH_NOSNAP)
> -		return NULL;
> +		return 0;
>   
>   restart:
>   	realm = ceph_inode(inode)->i_snap_realm;
> @@ -250,7 +251,7 @@ static struct ceph_snap_realm *get_quota_realm(struct ceph_mds_client *mdsc,
>   				break;
>   			ceph_put_snap_realm(mdsc, realm);
>   			if (!retry)
> -				return ERR_PTR(-EAGAIN);
> +				return -EAGAIN;
>   			goto restart;
>   		}
>   
> @@ -259,8 +260,11 @@ static struct ceph_snap_realm *get_quota_realm(struct ceph_mds_client *mdsc,
>   		iput(in);
>   
>   		next = realm->parent;
> -		if (has_quota || !next)
> -		       return realm;
> +		if (has_quota || !next) {
> +			if (realmp)
> +				*realmp = realm;
> +			return 0;
> +		}
>   
>   		ceph_get_snap_realm(mdsc, next);
>   		ceph_put_snap_realm(mdsc, realm);
> @@ -269,7 +273,7 @@ static struct ceph_snap_realm *get_quota_realm(struct ceph_mds_client *mdsc,
>   	if (realm)
>   		ceph_put_snap_realm(mdsc, realm);
>   
> -	return NULL;
> +	return 0;
>   }
>   
>   bool ceph_quota_is_same_realm(struct inode *old, struct inode *new)
> @@ -277,6 +281,7 @@ bool ceph_quota_is_same_realm(struct inode *old, struct inode *new)
>   	struct ceph_mds_client *mdsc = ceph_sb_to_mdsc(old->i_sb);
>   	struct ceph_snap_realm *old_realm, *new_realm;
>   	bool is_same;
> +	int ret;
>   
>   restart:
>   	/*
> @@ -286,9 +291,9 @@ bool ceph_quota_is_same_realm(struct inode *old, struct inode *new)
>   	 * dropped and we can then restart the whole operation.
>   	 */
>   	down_read(&mdsc->snap_rwsem);
> -	old_realm = get_quota_realm(mdsc, old, QUOTA_GET_ANY, true);
> -	new_realm = get_quota_realm(mdsc, new, QUOTA_GET_ANY, false);
> -	if (PTR_ERR(new_realm) == -EAGAIN) {
> +	get_quota_realm(mdsc, old, QUOTA_GET_ANY, &old_realm, true);
> +	ret = get_quota_realm(mdsc, new, QUOTA_GET_ANY, &new_realm, false);
> +	if (ret == -EAGAIN) {
>   		up_read(&mdsc->snap_rwsem);
>   		if (old_realm)
>   			ceph_put_snap_realm(mdsc, old_realm);
> @@ -492,8 +497,8 @@ bool ceph_quota_update_statfs(struct ceph_fs_client *fsc, struct kstatfs *buf)
>   	bool is_updated = false;
>   
>   	down_read(&mdsc->snap_rwsem);
> -	realm = get_quota_realm(mdsc, d_inode(fsc->sb->s_root),
> -				QUOTA_GET_MAX_BYTES, true);
> +	get_quota_realm(mdsc, d_inode(fsc->sb->s_root),
> +				QUOTA_GET_MAX_BYTES, &realm, true);

Some extra white spaces here.

Otherwise LGTM.

I will adjust it and applying it to the testing branch.

Thanks

- Xiubo

>   	up_read(&mdsc->snap_rwsem);
>   	if (!realm)
>   		return false;