CVE-2026-74738regmap: sdw-mbq: don't call an unset readable_reg callback

Official description

In the Linux kernel, the following vulnerability has been resolved: regmap: sdw-mbq: don't call an unset readable_reg callback regmap_sdw_mbq_poll_busy() decides whether to poll the Function Busy bit by calling ctx->readable_reg(), which is a straight copy of config->readable_reg. That callback is optional: regmap_readable() treats a NULL ->readable_reg as "every register is readable", and drivers rely on that. es9356 and tac5xx2-sdw both build an MBQ regmap without one. Since commit ca1b11b36d82 ("regmap: sdw-mbq: Allow defers on undeferrable controls") the poll runs on every -ENODATA, not only for Controls the driver marked deferrable, so any of those devices answering COMMAND_IGNORED takes the kernel through a NULL function pointer. Treat a missing callback the way the rest of regmap does and poll.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/6cf600b276a55a6481462830607a611f32e737c0
• https://git.kernel.org/stable/c/5bd8e897ecf558507142f4553e4526adfc1d6482
• https://git.kernel.org/stable/c/00268f9452d2a0d660aa9c1bb0ca07a994af6a4f