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    Subject[PATCH 5.4 228/314] gfs2: fix use-after-free on transaction ail lists
    Date
    From: Bob Peterson <rpeterso@redhat.com>

    [ Upstream commit 83d060ca8d90fa1e3feac227f995c013100862d3 ]

    Before this patch, transactions could be merged into the system
    transaction by function gfs2_merge_trans(), but the transaction ail
    lists were never merged. Because the ail flushing mechanism can run
    separately, bd elements can be attached to the transaction's buffer
    list during the transaction (trans_add_meta, etc) but quickly moved
    to its ail lists. Later, in function gfs2_trans_end, the transaction
    can be freed (by gfs2_trans_end) while it still has bd elements
    queued to its ail lists, which can cause it to either lose track of
    the bd elements altogether (memory leak) or worse, reference the bd
    elements after the parent transaction has been freed.

    Although I've not seen any serious consequences, the problem becomes
    apparent with the previous patch's addition of:

    gfs2_assert_warn(sdp, list_empty(&tr->tr_ail1_list));

    to function gfs2_trans_free().

    This patch adds logic into gfs2_merge_trans() to move the merged
    transaction's ail lists to the sdp transaction. This prevents the
    use-after-free. To do this properly, we need to hold the ail lock,
    so we pass sdp into the function instead of the transaction itself.

    Signed-off-by: Bob Peterson <rpeterso@redhat.com>
    Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    fs/gfs2/log.c | 11 +++++++++--
    1 file changed, 9 insertions(+), 2 deletions(-)

    diff --git a/fs/gfs2/log.c b/fs/gfs2/log.c
    index 110e5c4db8192..a4b6a49462a41 100644
    --- a/fs/gfs2/log.c
    +++ b/fs/gfs2/log.c
    @@ -881,8 +881,10 @@ void gfs2_log_flush(struct gfs2_sbd *sdp, struct gfs2_glock *gl, u32 flags)
    * @new: New transaction to be merged
    */

    -static void gfs2_merge_trans(struct gfs2_trans *old, struct gfs2_trans *new)
    +static void gfs2_merge_trans(struct gfs2_sbd *sdp, struct gfs2_trans *new)
    {
    + struct gfs2_trans *old = sdp->sd_log_tr;
    +
    WARN_ON_ONCE(!test_bit(TR_ATTACHED, &old->tr_flags));

    old->tr_num_buf_new += new->tr_num_buf_new;
    @@ -893,6 +895,11 @@ static void gfs2_merge_trans(struct gfs2_trans *old, struct gfs2_trans *new)

    list_splice_tail_init(&new->tr_databuf, &old->tr_databuf);
    list_splice_tail_init(&new->tr_buf, &old->tr_buf);
    +
    + spin_lock(&sdp->sd_ail_lock);
    + list_splice_tail_init(&new->tr_ail1_list, &old->tr_ail1_list);
    + list_splice_tail_init(&new->tr_ail2_list, &old->tr_ail2_list);
    + spin_unlock(&sdp->sd_ail_lock);
    }

    static void log_refund(struct gfs2_sbd *sdp, struct gfs2_trans *tr)
    @@ -904,7 +911,7 @@ static void log_refund(struct gfs2_sbd *sdp, struct gfs2_trans *tr)
    gfs2_log_lock(sdp);

    if (sdp->sd_log_tr) {
    - gfs2_merge_trans(sdp->sd_log_tr, tr);
    + gfs2_merge_trans(sdp, tr);
    } else if (tr->tr_num_buf_new || tr->tr_num_databuf_new) {
    gfs2_assert_withdraw(sdp, test_bit(TR_ALLOCED, &tr->tr_flags));
    sdp->sd_log_tr = tr;
    --
    2.25.1


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