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    Subject[PATCH 5.15 862/917] f2fs: fix UAF in f2fs_available_free_memory
    Date
    From: Dongliang Mu <mudongliangabcd@gmail.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@vger.kernel.org
    Fixes: d6d2b491a82e ("f2fs: allow to change discard policy based on cached discard cmds")
    Signed-off-by: Dongliang Mu <mudongliangabcd@gmail.com>
    Reviewed-by: Chao Yu <chao@kernel.org>
    Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    fs/f2fs/super.c | 2 ++
    1 file changed, 2 insertions(+)

    --- a/fs/f2fs/super.c
    +++ b/fs/f2fs/super.c
    @@ -4352,6 +4352,8 @@ 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);

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