Re: [PATCH] selftests: ublk: fix user_data truncation for tgt_data >= 256

[Ming Lei <ming.lei@redhat.com>]

On Thu, Oct 23, 2025 at 06:51:41PM +0800, Ming Lei wrote:
> The build_user_data() function packs multiple fields into a __u64
> value using bit shifts. Without explicit __u64 casts before shifting,
> the shift operations are performed on 32-bit unsigned integers before
> being promoted to 64-bit, causing data loss.
> 
> Specifically, when tgt_data >= 256, the expression (tgt_data << 24)
> shifts on a 32-bit value, truncating the upper 8 bits before promotion
> to __u64. Since tgt_data can be up to 16 bits (assertion allows up to
> 65535), values >= 256 would have their high byte lost.
> 
> Add explicit __u64 casts to both op and tgt_data before shifting to
> ensure the shift operations happen in 64-bit space, preserving all
> bits of the input values.
> 
> Fixes: 6aecda00b7d1 ("selftests: ublk: add kernel selftests for ublk")
> Signed-off-by: Ming Lei <ming.lei@redhat.com>

Hi Jens,

Looks this patch can't be applied cleanly, please ignore it, and sorry for
the noise.

Thanks,
Ming