lkml.org 
[lkml]   [2020]   [Sep]   [11]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [PATCH 4.19 142/206] gfs2: fix use-after-free on transaction ail lists
    On Thu, Sep 10, 2020 at 09:43:19PM +0200, Salvatore Bonaccorso wrote:
    > Hi,
    >
    > On Tue, Jun 23, 2020 at 09:57:50PM +0200, Greg Kroah-Hartman wrote:
    > > 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 d3f0612e33471..06752db213d21 100644
    > > --- a/fs/gfs2/log.c
    > > +++ b/fs/gfs2/log.c
    > > @@ -877,8 +877,10 @@ 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;
    > > @@ -890,6 +892,11 @@ 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)
    > > @@ -901,7 +908,7 @@ 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
    >
    > In Debian two user confirmed issues on writing on a GFS2 partition
    > with this commit applied. The initial Debian report is at
    > https://bugs.debian.org/968567 and Daniel Craig reported it into
    > Bugzilla at https://bugzilla.kernel.org/show_bug.cgi?id=209217 .
    >
    > Writing to a gfs2 filesystem fails and results in a soft lookup of the
    > machine for kernels with that commit applied. I cannot reporduce the
    > issue myself due not having a respective setup available, but Daniel
    > described a minimal serieos of steps to reproduce the issue.
    >
    > This might affect as well other stable series where this commit was
    > applied, as there was a similar report for someone running 5.4.58 in
    > https://www.redhat.com/archives/linux-cluster/2020-August/msg00000.html

    Can you report this to the gfs2 developers?

    thanks,

    greg k-h

    \
     
     \ /
      Last update: 2020-09-11 13:59    [W:5.532 / U:0.048 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site