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    Subject[PATCH 5.4 146/191] xfs: fix mount failure crash on invalid iclog memory access
    Date
    From: Brian Foster <bfoster@redhat.com>

    commit 798a9cada4694ca8d970259f216cec47e675bfd5 upstream.

    syzbot (via KASAN) reports a use-after-free in the error path of
    xlog_alloc_log(). Specifically, the iclog freeing loop doesn't
    handle the case of a fully initialized ->l_iclog linked list.
    Instead, it assumes that the list is partially constructed and NULL
    terminated.

    This bug manifested because there was no possible error scenario
    after iclog list setup when the original code was added. Subsequent
    code and associated error conditions were added some time later,
    while the original error handling code was never updated. Fix up the
    error loop to terminate either on a NULL iclog or reaching the end
    of the list.

    Reported-by: syzbot+c732f8644185de340492@syzkaller.appspotmail.com
    Signed-off-by: Brian Foster <bfoster@redhat.com>
    Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
    Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    fs/xfs/xfs_log.c | 2 ++
    1 file changed, 2 insertions(+)

    --- a/fs/xfs/xfs_log.c
    +++ b/fs/xfs/xfs_log.c
    @@ -1495,6 +1495,8 @@ out_free_iclog:
    prev_iclog = iclog->ic_next;
    kmem_free(iclog->ic_data);
    kmem_free(iclog);
    + if (prev_iclog == log->l_iclog)
    + break;
    }
    out_free_log:
    kmem_free(log);

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