linux-kernel - [PATCH] fs: f2fs: fix UAF in f2fs_available_free

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Message-Id: <20211103142228.1235864-1-mudongliangabcd@gmail.com>
Date:   Wed,  3 Nov 2021 22:22:27 +0800
From:   Dongliang Mu <mudongliangabcd@...il.com>
To:     Jaegeuk Kim <jaegeuk@...nel.org>, Chao Yu <chao@...nel.org>
Cc:     Dongliang Mu <mudongliangabcd@...il.com>,
        linux-f2fs-devel@...ts.sourceforge.net,
        linux-kernel@...r.kernel.org
Subject: [PATCH] fs: f2fs: fix UAF in f2fs_available_free_memory

f2fs_fill_super
-> f2fs_build_segment_manager
   -> create_discard_cmd_control
      -> f2fs_start_discard_thread

It invokes kthread_run to create a thread and run issue_discard_thread.

However, if f2fs_build_node_manager fails, the control flow goes to
free_nm and calls f2fs_destroy_node_manager. This function will free
sbi->nm_info. However, if issue_discard_thread accesses sbi->nm_info
after the deallocation, but before the f2fs_stop_discard_thread, it will
cause UAF(Use-after-free).

-> f2fs_destroy_segment_manager
   -> destroy_discard_cmd_control
      -> f2fs_stop_discard_thread

Fix this by switching the order of f2fs_build_segment_manager
and f2fs_build_node_manager.

Signed-off-by: Dongliang Mu <mudongliangabcd@...il.com>
---
 fs/f2fs/super.c | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
index 78ebc306ee2b..1a23b64cfb74 100644
--- a/fs/f2fs/super.c
+++ b/fs/f2fs/super.c
@@ -4135,18 +4135,18 @@ static int f2fs_fill_super(struct super_block *sb, void *data, int silent)
 	}
 
 	/* setup f2fs internal modules */
-	err = f2fs_build_segment_manager(sbi);
-	if (err) {
-		f2fs_err(sbi, "Failed to initialize F2FS segment manager (%d)",
-			 err);
-		goto free_sm;
-	}
 	err = f2fs_build_node_manager(sbi);
 	if (err) {
 		f2fs_err(sbi, "Failed to initialize F2FS node manager (%d)",
 			 err);
 		goto free_nm;
 	}
+	err = f2fs_build_segment_manager(sbi);
+	if (err) {
+		f2fs_err(sbi, "Failed to initialize F2FS segment manager (%d)",
+			 err);
+		goto free_sm;
+	}
 
 	/* For write statistics */
 	sbi->sectors_written_start = f2fs_get_sectors_written(sbi);
@@ -4351,10 +4351,10 @@ static int f2fs_fill_super(struct super_block *sb, void *data, int silent)
 	sbi->node_inode = NULL;
 free_stats:
 	f2fs_destroy_stats(sbi);
-free_nm:
-	f2fs_destroy_node_manager(sbi);
 free_sm:
 	f2fs_destroy_segment_manager(sbi);
+free_nm:
+	f2fs_destroy_node_manager(sbi);
 	f2fs_destroy_post_read_wq(sbi);
 stop_ckpt_thread:
 	f2fs_stop_ckpt_thread(sbi);
-- 
2.25.1