CVE-2025-39686

In the Linux kernel, the following vulnerability has been resolved:

comedi: Make insnrwemulate_bits() do insn->n samples

The insn_rw_emulate_bits() function is used as a default handler for INSN_READ instructions for subdevices that have a handler for INSN_BITS but not for INSN_READ. Similarly, it is used as a default handler for INSN_WRITE instructions for subdevices that have a handler for INSN_BITS but not for INSN_WRITE. It works by emulating the INSN_READ or INSN_WRITE instruction handling with a constructed INSN_BITS instruction. However, INSN_READ and INSN_WRITE instructions are supposed to be able read or write multiple samples, indicated by the insn->n value, but insn_rw_emulate_bits() currently only handles a single sample. For INSN_READ, the comedi core will copy insn->n samples back to user-space. (That triggered KASAN kernel-infoleak errors when insn->n was greater than 1, but that is being fixed more generally elsewhere in the comedi core.)

Make insn_rw_emulate_bits() either handle insn->n samples, or return an error, to conform to the general expectation for INSN_READ and INSN_WRITE handlers.