CVE-2024-35827

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

io_uring/net: fix overflow check in io_recvmsg_mshot_prep()

The "controllen" variable is type size_t (unsigned long). Casting it to int could lead to an integer underflow.

The check_add_overflow() function considers the type of the destination which is type int. If we add two positive values and the result cannot fit in an integer then that's counted as an overflow.

However, if we cast "controllen" to an int and it turns negative, then negative values *can* fit into an int type so there is no overflow.

Good: 100 + (unsigned long)-4 = 96 <-- overflow Bad: 100 + (int)-4 = 96 <-- no overflow

I deleted the cast of the sizeof() as well. That's not a bug but the cast is unnecessary.