erofs: fix erofs_insert_workgroup() lockref usage

[ Upstream commit 1a0ac8bd7a4fa5b2f4ef14c3b1e9d6e5a5faae06 ]

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: 7674a42f35ea ("erofs: use struct lockref to replace handcrafted approach")
Reviewed-by: Chao Yu <chao@kernel.org>
Link: https://lore.kernel.org/r/20231031060524.1103921-1-hsiangkao@linux.alibaba.com
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/fs/erofs/utils.c b/fs/erofs/utils.c
index cc6fb9e98899174662a77bca865846d1884e726b..4256a85719a1d25fbe3f0aa33820fafe3ad01d45 100644 (file)
--- a/fs/erofs/utils.c
+++ b/fs/erofs/utils.c
@@ -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 @@ repeat:
                        cond_resched();
                        goto repeat;
                }
-               lockref_put_return(&grp->lockref);
                grp = pre;
        }
        xa_unlock(&sbi->managed_pslots);

diff --git a/fs/erofs/zdata.c b/fs/erofs/zdata.c
index 9bfdb4ad7c7630147da94ce6662cf36bb29073ed..2461a3f74e744532206be6a871c11086e61c96e5 100644 (file)
--- a/fs/erofs/zdata.c
+++ b/fs/erofs/zdata.c
@@ -805,6 +805,7 @@ 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;