dm: fix a buffer overflow in ioctl processing

CVE-2026-46294

What is CVE-2026-46294?

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

dm: fix a buffer overflow in ioctl processing

Tony Asleson (using Claude) found a buffer overflow in dm-ioctl in the function retrieve_status:

1. The code in retrieve_status checks that the output string fits into the output buffer and writes the output string there
2. Then, the code aligns the "outptr" variable to the next 8-byte boundary: outptr = align_ptr(outptr);
3. The alignment doesn't check overflow, so outptr could point past the buffer end
4. The "for" loop is iterated again, it executes: remaining = len - (outptr - outbuf);
5. If "outptr" points past "outbuf + len", the arithmetics wraps around and the variable "remaining" contains unusually high number
6. With "remaining" being high, the code writes more data past the end of the buffer

Luckily, this bug has no security implications because:

1. Only root can issue device mapper ioctls
2. The commonly used libraries that communicate with device mapper (libdevmapper and devicemapper-rs) use buffer size that is aligned to 8 bytes - thus, "outptr = align_ptr(outptr)" can't overshoot the input buffer and the bug can't happen accidentally

References