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    Subject[PATCH AUTOSEL 4.19 12/55] reiserfs: add check for invalid 1st journal block
    Date
    From: Pavel Skripkin <paskripkin@gmail.com>

    [ Upstream commit a149127be52fa7eaf5b3681a0317a2bbb772d5a9 ]

    syzbot reported divide error in reiserfs.
    The problem was in incorrect journal 1st block.

    Syzbot's reproducer manualy generated wrong superblock
    with incorrect 1st block. In journal_init() wasn't
    any checks about this particular case.

    For example, if 1st journal block is before superblock
    1st block, it can cause zeroing important superblock members
    in do_journal_end().

    Link: https://lore.kernel.org/r/20210517121545.29645-1-paskripkin@gmail.com
    Reported-by: syzbot+0ba9909df31c6a36974d@syzkaller.appspotmail.com
    Signed-off-by: Pavel Skripkin <paskripkin@gmail.com>
    Signed-off-by: Jan Kara <jack@suse.cz>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    fs/reiserfs/journal.c | 14 ++++++++++++++
    1 file changed, 14 insertions(+)

    diff --git a/fs/reiserfs/journal.c b/fs/reiserfs/journal.c
    index 8a76f9d14bc6..78be6dbcd762 100644
    --- a/fs/reiserfs/journal.c
    +++ b/fs/reiserfs/journal.c
    @@ -2772,6 +2772,20 @@ int journal_init(struct super_block *sb, const char *j_dev_name,
    goto free_and_return;
    }

    + /*
    + * Sanity check to see if journal first block is correct.
    + * If journal first block is invalid it can cause
    + * zeroing important superblock members.
    + */
    + if (!SB_ONDISK_JOURNAL_DEVICE(sb) &&
    + SB_ONDISK_JOURNAL_1st_BLOCK(sb) < SB_JOURNAL_1st_RESERVED_BLOCK(sb)) {
    + reiserfs_warning(sb, "journal-1393",
    + "journal 1st super block is invalid: 1st reserved block %d, but actual 1st block is %d",
    + SB_JOURNAL_1st_RESERVED_BLOCK(sb),
    + SB_ONDISK_JOURNAL_1st_BLOCK(sb));
    + goto free_and_return;
    + }
    +
    if (journal_init_dev(sb, journal, j_dev_name) != 0) {
    reiserfs_warning(sb, "sh-462",
    "unable to initialize journal device");
    --
    2.30.2
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