Re: [syzbot] [netfs?] KASAN: slab-use-after-free Write in __fscache_relinquish_cookie

[Edward Adam Davis]

please test uaf in __fscache_relinquish_cookie

#syz test https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git master 
diff --git a/fs/9p/vfs_inode.c b/fs/9p/vfs_inode.c
index 360a5304ec03..e36467ed618f 100644
--- a/fs/9p/vfs_inode.c
+++ b/fs/9p/vfs_inode.c
@@ -353,7 +353,9 @@ void v9fs_evict_inode(struct inode *inode)
 	filemap_fdatawrite(&inode->i_data);
 
 #ifdef CONFIG_9P_FSCACHE
-	fscache_relinquish_cookie(v9fs_inode_cookie(v9inode), false);
+	printk("mra: %d, %s\n", mapping_release_always(inode->i_mapping), __func__);
+	if (mapping_release_always(inode->i_mapping))
+		fscache_relinquish_cookie(v9fs_inode_cookie(v9inode), false);
 #endif
 }
 
diff --git a/fs/9p/vfs_inode_dotl.c b/fs/9p/vfs_inode_dotl.c
index ef9db3e03506..fd26bafe4279 100644
--- a/fs/9p/vfs_inode_dotl.c
+++ b/fs/9p/vfs_inode_dotl.c
@@ -78,6 +78,7 @@ struct inode *v9fs_fid_iget_dotl(struct super_block *sb, struct p9_fid *fid)
 
 	retval = v9fs_init_inode(v9ses, inode, &fid->qid,
 				 st->st_mode, new_decode_dev(st->st_rdev));
+	printk("mra: %d, %s\n", mapping_release_always(inode->i_mapping), __func__);
 	kfree(st);
 	if (retval)
 		goto error;
@@ -86,6 +87,7 @@ struct inode *v9fs_fid_iget_dotl(struct super_block *sb, struct p9_fid *fid)
 	v9fs_set_netfs_context(inode);
 	v9fs_cache_inode_get_cookie(inode);
 	retval = v9fs_get_acl(inode, fid);
+	printk("2mra: %d, %s\n", mapping_release_always(inode->i_mapping), __func__);
 	if (retval)
 		goto error;