CVE-2025-38480

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

comedi: Fix use of uninitialized data in insn_rw_emulate_bits()

For Comedi INSN_READ and INSN_WRITE instructions on digital subdevices (subdevice types COMEDI_SUBD_DI, COMEDI_SUBD_DO, and COMEDI_SUBD_DIO), it is common for the subdevice driver not to have insn_read and insn_write handler functions, but to have an insn_bits handler function for handling Comedi INSN_BITS instructions. In that case, the subdevices insn_read and/or insn_write function handler pointers are set to point to the insn_rw_emulate_bits() function by __comedi_device_postconfig().

For INSN_WRITE, insn_rw_emulate_bits() currently assumes that the supplied data[0] value is a valid copy from user memory. It will at least exist because do_insnlist_ioctl() and do_insn_ioctl() in comedi_fops.c ensure at lease MIN_SAMPLES (16) elements are allocated. However, if insn->n is 0 (which is allowable for INSN_READ and INSN_WRITE instructions, then data[0] may contain uninitialized data, and certainly contains invalid data, possibly from a different instruction in the array of instructions handled by do_insnlist_ioctl(). This will result in an incorrect value being written to the digital output channel (or to the digital input/output channel if configured as an output), and may be reflected in the internal saved state of the channel.

Fix it by returning 0 early if insn->n is 0, before reaching the code that accesses data[0]. Previously, the function always returned 1 on success, but it is supposed to be the number of data samples actually read or written up to insn->n, which is 0 in this case.

Affected Software

References

• https://git.kernel.org/stable/c/10f9024a8c824a41827fff1fefefb314c98e2c88
• https://git.kernel.org/stable/c/2af1e7d389c2619219171d23f5b96dbcbb7f9656
• https://git.kernel.org/stable/c/3050d197d6bc9ef128944a70210f42d2430b3000
• https://git.kernel.org/stable/c/3ab55ffaaf75d0c7b68e332c1cdcc1b0e0044870
• https://git.kernel.org/stable/c/e9cb26291d009243a4478a7ffb37b3a9175bfce9