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    Subject[PATCH 4.9 249/264] ext4: add reserved GDT blocks check
    Date
    From: Zhang Yi <yi.zhang@huawei.com>

    commit b55c3cd102a6f48b90e61c44f7f3dda8c290c694 upstream.

    We capture a NULL pointer issue when resizing a corrupt ext4 image which
    is freshly clear resize_inode feature (not run e2fsck). It could be
    simply reproduced by following steps. The problem is because of the
    resize_inode feature was cleared, and it will convert the filesystem to
    meta_bg mode in ext4_resize_fs(), but the es->s_reserved_gdt_blocks was
    not reduced to zero, so could we mistakenly call reserve_backup_gdb()
    and passing an uninitialized resize_inode to it when adding new group
    descriptors.

    mkfs.ext4 /dev/sda 3G
    tune2fs -O ^resize_inode /dev/sda #forget to run requested e2fsck
    mount /dev/sda /mnt
    resize2fs /dev/sda 8G

    ========
    BUG: kernel NULL pointer dereference, address: 0000000000000028
    CPU: 19 PID: 3243 Comm: resize2fs Not tainted 5.18.0-rc7-00001-gfde086c5ebfd #748
    ...
    RIP: 0010:ext4_flex_group_add+0xe08/0x2570
    ...
    Call Trace:
    <TASK>
    ext4_resize_fs+0xbec/0x1660
    __ext4_ioctl+0x1749/0x24e0
    ext4_ioctl+0x12/0x20
    __x64_sys_ioctl+0xa6/0x110
    do_syscall_64+0x3b/0x90
    entry_SYSCALL_64_after_hwframe+0x44/0xae
    RIP: 0033:0x7f2dd739617b
    ========

    The fix is simple, add a check in ext4_resize_begin() to make sure that
    the es->s_reserved_gdt_blocks is zero when the resize_inode feature is
    disabled.

    Cc: stable@kernel.org
    Signed-off-by: Zhang Yi <yi.zhang@huawei.com>
    Reviewed-by: Ritesh Harjani <ritesh.list@gmail.com>
    Reviewed-by: Jan Kara <jack@suse.cz>
    Link: https://lore.kernel.org/r/20220601092717.763694-1-yi.zhang@huawei.com
    Signed-off-by: Theodore Ts'o <tytso@mit.edu>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    fs/ext4/resize.c | 10 ++++++++++
    1 file changed, 10 insertions(+)

    --- a/fs/ext4/resize.c
    +++ b/fs/ext4/resize.c
    @@ -52,6 +52,16 @@ int ext4_resize_begin(struct super_block
    return -EPERM;

    /*
    + * If the reserved GDT blocks is non-zero, the resize_inode feature
    + * should always be set.
    + */
    + if (EXT4_SB(sb)->s_es->s_reserved_gdt_blocks &&
    + !ext4_has_feature_resize_inode(sb)) {
    + ext4_error(sb, "resize_inode disabled but reserved GDT blocks non-zero");
    + return -EFSCORRUPTED;
    + }
    +
    + /*
    * If we are not using the primary superblock/GDT copy don't resize,
    * because the user tools have no way of handling this. Probably a
    * bad time to do it anyways.

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