Reviewed-by: Yehuda Sadeh <yehuda@xxxxxxxxxxx>
On Thu, Sep 6, 2012 at 8:36 AM, Alex Elder <elder@xxxxxxxxxxx> wrote:
> The only thing the on-disk snap_names_len field is needed is to
> size the buffer allocated to hold a copy of the snapshot names
> for an rbd image.
>
> So don't bother saving it in the in-core rbd_image_header structure.
> Just use a local variable to hold the required buffer size while
> it's needed.
>
> Move the code that actually copies the snapshot names up closer
> to where the required length is saved.
>
> Signed-off-by: Alex Elder <elder@xxxxxxxxxxx>
> ---
> v2: - Return -EIO rather than BUG_ON() as suggested by Yehuda.
> - Added a comment explaining why a memcpy() will not exceed
> the length of the on-disk buffer, in response to Yehuda's
> concern.
>
> drivers/block/rbd.c | 26 +++++++++++++-------------
> 1 file changed, 13 insertions(+), 13 deletions(-)
>
> Index: b/drivers/block/rbd.c
> ===================================================================
> --- a/drivers/block/rbd.c
> +++ b/drivers/block/rbd.c
> @@ -81,7 +81,6 @@ struct rbd_image_header {
> __u8 crypt_type;
> __u8 comp_type;
> struct ceph_snap_context *snapc;
> - u64 snap_names_len;
> u32 total_snaps;
>
> char *snap_names;
> @@ -534,12 +533,21 @@ static int rbd_header_from_disk(struct r
> header->object_prefix[len] = '\0';
>
> if (snap_count) {
> - header->snap_names_len = le64_to_cpu(ondisk->snap_names_len);
> - BUG_ON(header->snap_names_len > (u64) SIZE_MAX);
> - header->snap_names = kmalloc(header->snap_names_len,
> - GFP_KERNEL);
> + u64 snap_names_len = le64_to_cpu(ondisk->snap_names_len);
> +
> + if (snap_names_len > (u64) SIZE_MAX)
> + return -EIO;
> + header->snap_names = kmalloc(snap_names_len, GFP_KERNEL);
> if (!header->snap_names)
> goto out_err;
> + /*
> + * Note that rbd_dev_v1_header_read() guarantees
> + * the ondisk buffer we're working with has
> + * snap_names_len bytes beyond the end of the
> + * snapshot id array, this memcpy() is safe.
> + */
> + memcpy(header->snap_names, &ondisk->snaps[snap_count],
> + snap_names_len);
>
> size = snap_count * sizeof (*header->snap_sizes);
> header->snap_sizes = kmalloc(size, GFP_KERNEL);
> @@ -547,7 +555,6 @@ static int rbd_header_from_disk(struct r
> goto out_err;
> } else {
> WARN_ON(ondisk->snap_names_len);
> - header->snap_names_len = 0;
> header->snap_names = NULL;
> header->snap_sizes = NULL;
> }
> @@ -579,10 +586,6 @@ static int rbd_header_from_disk(struct r
> header->snap_sizes[i] =
> le64_to_cpu(ondisk->snaps[i].image_size);
> }
> -
> - /* copy snapshot names */
> - memcpy(header->snap_names, &ondisk->snaps[snap_count],
> - header->snap_names_len);
> }
>
> return 0;
> @@ -592,7 +595,6 @@ out_err:
> header->snap_sizes = NULL;
> kfree(header->snap_names);
> header->snap_names = NULL;
> - header->snap_names_len = 0;
> kfree(header->object_prefix);
> header->object_prefix = NULL;
>
> @@ -660,7 +662,6 @@ static void rbd_header_free(struct rbd_i
> header->snap_sizes = NULL;
> kfree(header->snap_names);
> header->snap_names = NULL;
> - header->snap_names_len = 0;
> ceph_put_snap_context(header->snapc);
> header->snapc = NULL;
> }
> @@ -1800,7 +1801,6 @@ static int __rbd_refresh_header(struct r
> rbd_dev->header.total_snaps = h.total_snaps;
> rbd_dev->header.snapc = h.snapc;
> rbd_dev->header.snap_names = h.snap_names;
> - rbd_dev->header.snap_names_len = h.snap_names_len;
> rbd_dev->header.snap_sizes = h.snap_sizes;
> /* Free the extra copy of the object prefix */
> WARN_ON(strcmp(rbd_dev->header.object_prefix, h.object_prefix));
>
> --
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