linux-kernel - [PATCH 5.14 798/849] f2fs: fix UAF in f2fs_available_free

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Message-Id: <20211115165447.230649140@linuxfoundation.org>
Date:   Mon, 15 Nov 2021 18:04:41 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Dongliang Mu <mudongliangabcd@...il.com>,
        Chao Yu <chao@...nel.org>, Jaegeuk Kim <jaegeuk@...nel.org>
Subject: [PATCH 5.14 798/849] f2fs: fix UAF in f2fs_available_free_memory

From: Dongliang Mu <mudongliangabcd@...il.com>

commit 5429c9dbc9025f9a166f64e22e3a69c94fd5b29b upstream.

if2fs_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 stopping discard thread before f2fs_destroy_node_manager.

Note that, the commit d6d2b491a82e1 introduces the call of
f2fs_available_free_memory into issue_discard_thread.

Cc: stable@...r.kernel.org
Fixes: d6d2b491a82e ("f2fs: allow to change discard policy based on cached discard cmds")
Signed-off-by: Dongliang Mu <mudongliangabcd@...il.com>
Reviewed-by: Chao Yu <chao@...nel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@...nel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 fs/f2fs/super.c |    2 ++
 1 file changed, 2 insertions(+)

--- a/fs/f2fs/super.c
+++ b/fs/f2fs/super.c
@@ -4271,6 +4271,8 @@ free_node_inode:
 free_stats:
 	f2fs_destroy_stats(sbi);
 free_nm:
+	/* stop discard thread before destroying node manager */
+	f2fs_stop_discard_thread(sbi);
 	f2fs_destroy_node_manager(sbi);
 free_sm:
 	f2fs_destroy_segment_manager(sbi);