Re: [PATCH] media: v4l2-isp: reject zero-sized parameter blocks

[David CARLIER]

Hi Jacopo,

On Mon, Aug 17, 2026 at 11:59:15AM +0200, Jacopo Mondi wrote:
> > whenever the driver's type_info[] entry is an uninitialised hole, so
>
> This shouldn't happen (an empty type_info[] I mean)
[...]
> > held. rppx1 has such a hole today; fix the core so the walk terminates
>
> Uh, where ?

Sorry, I should have spelled this out in the commit message.

RPPX1_PARAMS_BLOCK_INFO() is a designated initialiser indexed by the
block type (rpp_params.c:13):

      #define RPPX1_PARAMS_BLOCK_INFO(block, data) \
              [RPPX1_PARAMS_BLOCK_TYPE_ ## block] = { \
                      .size = sizeof(struct rppx1_ ## data ## _params), \
              }

so the list reads as dense but is indexed by the enum. It has 17
entries for 18 enumerators, and the missing one is AWBG_POST (== 3).
The last index used is LIN_PRE2 (== 17), so ARRAY_SIZE() is still 18
and the entry at 3 is simply zeroed.

A block with type AWBG_POST and size 0 then gets through: 0 is not
larger than the remaining buffer, and block->size != info->size is
0 != 0. block_offset and buffer_size don't move and the loop spins,
in .buf_prepare, holding the queue mutex.

> I'm not against this, but it only makes sense if the driver populates
> the list of v4l2_isp_params_block_type_info[] with an empty item,
> which shouldn't happen.

True, and rppx1 is the only one that does - rkisp1, c3-isp and
mali-c55 all look complete. What bothers me is that the loop only
terminates if every driver's table is right, and nothing checks that
at build time. A missing line in a driver would be a rejected buffer
rather than a stuck task. And a block size below its own header is
malformed anyway, whatever the type.

That said, rppx1 needs a patch either way: AWBG_POST is documented i
rppx1-config.h and the driver probes rpp->post.awbg, but the block
can't be used today - the size check compares against 0, and
rppx1_params() has no case for it in the switch.

Happy to drop a separate patch and keep only the driver fix if you prefer.

Cheers.