On 08/30/2012 11:24 AM, Yehuda Sadeh wrote:
> On Fri, Aug 24, 2012 at 9:33 AM, Alex Elder <elder@xxxxxxxxxxx> wrote:
>> The only thing the on-disk snap_names_len field is used for is to
>> size the buffer allocated to hold a copy of the snapshot names for
>> an rbd image.
>>
>> 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>
>> ---
>> drivers/block/rbd.c | 19 ++++++-------------
>> 1 file changed, 6 insertions(+), 13 deletions(-)
>>
>> diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c
>> index a8a4cba..7b3d861 100644
>> --- 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 +533,14 @@ static int rbd_header_from_disk(struct
>> rbd_image_header *header,
>> 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);
>> +
>> + BUG_ON(snap_names_len > (u64) SIZE_MAX);
>
> Should we get rid of this BUG_ON and return -EIO instead?
Yes. I've been using BUG_ON() a bit freely and I'd really like
to define a CEPH_ASSERT() or something instead. In this case I
can return an error value so I will.
I'll define CEPH_ASSERT() at some point, separately so I can
state assumptions without potentially killing the kernel.
>> + header->snap_names = kmalloc(snap_names_len, GFP_KERNEL);
>> if (!header->snap_names)
>> goto out_err;
>> + memcpy(header->snap_names, &ondisk->snaps[snap_count],
>> + snap_names_len);
>
> I think we're missing a check here to verify that we don't exceed the
> ondisk buffer
I believe in this case we're OK, though it's not obvious looking
only at this code. (I'm looking at code with all these patches
applied at the moment, so I may need to reorder the patches for the
following explanation to be valid.)
The ondisk buffer passed in here came from a successful call to
what's now called rbd_dev_v1_header_read(), which reads the
header in *only*, and only succeeds if it got everything it
was looking for--namely the snapshot context, plus the size
of the set of names that the context says will follow. It
will furthermore re-read the header if the count of snapshots
found in what got read differed from what we wanted it to be.
Therefore the ondisk header+names buffer here will always be
self-consistent--there will be room in the buffer for exactly
the number of bytes to hold the set of NUL-terminated snapshot
names.
If I could find an easy way to verify this here I would, but
right now the size of the ondisk buffer passed in is not
available. If you think it's important I can make changes
so it is though.
And in any case, before I commit anything I'll take another
look at this patch and maybe reorder things so the above
argument holds water.
-Alex
>>
>> size = snap_count * sizeof (*header->snap_sizes);
>> header->snap_sizes = kmalloc(size, GFP_KERNEL);
>> @@ -547,7 +548,6 @@ static int rbd_header_from_disk(struct
>> rbd_image_header *header,
>> 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 +579,6 @@ static int rbd_header_from_disk(struct
>> rbd_image_header *header,
>> 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 +588,6 @@ 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 +655,6 @@ static void rbd_header_free(struct rbd_image_header
>> *header)
>> 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 +1794,6 @@ static int __rbd_refresh_header(struct rbd_device
>> *rbd_dev, u64 *hver)
>> 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));
>> --
>> 1.7.9.5
>>
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>
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