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    Subject[PATCH 3.16 103/132] GFS2: don't set rgrp gl_object until it's inserted into rgrp tree
    3.16.74-rc1 review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Bob Peterson <rpeterso@redhat.com>

    commit 36e4ad0316c017d5b271378ed9a1c9a4b77fab5f upstream.

    Before this patch, function read_rindex_entry would set a rgrp
    glock's gl_object pointer to itself before inserting the rgrp into
    the rgrp rbtree. The problem is: if another process was also reading
    the rgrp in, and had already inserted its newly created rgrp, then
    the second call to read_rindex_entry would overwrite that value,
    then return a bad return code to the caller. Later, other functions
    would reference the now-freed rgrp memory by way of gl_object.
    In some cases, that could result in gfs2_rgrp_brelse being called
    twice for the same rgrp: once for the failed attempt and once for
    the "real" rgrp release. Eventually the kernel would panic.
    There are also a number of other things that could go wrong when
    a kernel module is accessing freed storage. For example, this could
    result in rgrp corruption because the fake rgrp would point to a
    fake bitmap in memory too, causing gfs2_inplace_reserve to search
    some random memory for free blocks, and find some, since we were
    never setting rgd->rd_bits to NULL before freeing it.

    This patch fixes the problem by not setting gl_object until we
    have successfully inserted the rgrp into the rbtree. Also, it sets
    rd_bits to NULL as it frees them, which will ensure any accidental
    access to the wrong rgrp will result in a kernel panic rather than
    file system corruption, which is preferred.

    Signed-off-by: Bob Peterson <rpeterso@redhat.com>
    [bwh: Backported to 3.16: adjust context]
    Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
    ---
    --- a/fs/gfs2/rgrp.c
    +++ b/fs/gfs2/rgrp.c
    @@ -731,6 +731,7 @@ void gfs2_clear_rgrpd(struct gfs2_sbd *s

    gfs2_free_clones(rgd);
    kfree(rgd->rd_bits);
    + rgd->rd_bits = NULL;
    return_all_reservations(rgd);
    kmem_cache_free(gfs2_rgrpd_cachep, rgd);
    }
    @@ -925,10 +926,6 @@ static int read_rindex_entry(struct gfs2
    if (error)
    goto fail;

    - rgd->rd_gl->gl_object = rgd;
    - rgd->rd_gl->gl_vm.start = (rgd->rd_addr * bsize) & PAGE_CACHE_MASK;
    - rgd->rd_gl->gl_vm.end = PAGE_CACHE_ALIGN((rgd->rd_addr +
    - rgd->rd_length) * bsize) - 1;
    rgd->rd_rgl = (struct gfs2_rgrp_lvb *)rgd->rd_gl->gl_lksb.sb_lvbptr;
    rgd->rd_flags &= ~GFS2_RDF_UPTODATE;
    if (rgd->rd_data > sdp->sd_max_rg_data)
    @@ -936,14 +933,20 @@ static int read_rindex_entry(struct gfs2
    spin_lock(&sdp->sd_rindex_spin);
    error = rgd_insert(rgd);
    spin_unlock(&sdp->sd_rindex_spin);
    - if (!error)
    + if (!error) {
    + rgd->rd_gl->gl_object = rgd;
    + rgd->rd_gl->gl_vm.start = (rgd->rd_addr * bsize) & PAGE_MASK;
    + rgd->rd_gl->gl_vm.end = PAGE_ALIGN((rgd->rd_addr +
    + rgd->rd_length) * bsize) - 1;
    return 0;
    + }

    error = 0; /* someone else read in the rgrp; free it and ignore it */
    gfs2_glock_put(rgd->rd_gl);

    fail:
    kfree(rgd->rd_bits);
    + rgd->rd_bits = NULL;
    kmem_cache_free(gfs2_rgrpd_cachep, rgd);
    return error;
    }
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