Commit 1a0ac8bd authored by Gao Xiang's avatar Gao Xiang
Browse files

erofs: fix erofs_insert_workgroup() lockref usage 

As Linus pointed out [1], lockref_put_return() is fundamentally
designed to be something that can fail.  It behaves as a fastpath-only
thing, and the failure case needs to be handled anyway.

Actually, since the new pcluster was just allocated without being
populated, it won't be accessed by others until it is inserted into
XArray, so lockref helpers are actually unneeded here.

Let's just set the proper reference count on initializing.

[1] https://lore.kernel.org/r/CAHk-=whCga8BeQnJ3ZBh_Hfm9ctba_wpF444LpwRybVNMzO6Dw@mail.gmail.com



Fixes: 7674a42f ("erofs: use struct lockref to replace handcrafted approach")
Reviewed-by: default avatarChao Yu <chao@kernel.org>
Link: https://lore.kernel.org/r/20231031060524.1103921-1-hsiangkao@linux.alibaba.com


Signed-off-by: default avatarGao Xiang <hsiangkao@linux.alibaba.com>
parent f5deddce

fs/erofs/utils.c

+1 −7
Original line number Diff line number Diff line
@@ -77,12 +77,7 @@ struct erofs_workgroup *erofs_insert_workgroup(struct super_block *sb, 
	struct erofs_sb_info *const sbi = EROFS_SB(sb);

	struct erofs_workgroup *pre;



	/*

	 * Bump up before making this visible to others for the XArray in order

	 * to avoid potential UAF without serialized by xa_lock.

	 */

	lockref_get(&grp->lockref);



	DBG_BUGON(grp->lockref.count < 1);

repeat:

	xa_lock(&sbi->managed_pslots);

	pre = __xa_cmpxchg(&sbi->managed_pslots, grp->index,
@@ -96,7 +91,6 @@ struct erofs_workgroup *erofs_insert_workgroup(struct super_block *sb, 
			cond_resched();

			goto repeat;

		}

		lockref_put_return(&grp->lockref);

		grp = pre;

	}

	xa_unlock(&sbi->managed_pslots);

fs/erofs/zdata.c

+1 −0
Original line number Diff line number Diff line
@@ -796,6 +796,7 @@ static int z_erofs_register_pcluster(struct z_erofs_decompress_frontend *fe) 
		return PTR_ERR(pcl);



	spin_lock_init(&pcl->obj.lockref.lock);

	pcl->obj.lockref.count = 1;	/* one ref for this request */

	pcl->algorithmformat = map->m_algorithmformat;

	pcl->length = 0;

	pcl->partial = true;