io_uring/memmap: cast nr_pages to size_t before shifting

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: io_uring/memmap: cast nr_pages to size_t before shifting If the allocated size exceeds UINT_MAX, then it's necessary to cast the mr->nr_pages value to size_t to prevent it from overflowing. In practice this isn't much of a concern as the required memory size will have been validated upfront, and accounted to the user. And > 4GB sizes will be necessary to make the lack of a cast a problem, which greatly exceeds normal user locked_vm settings that are generally in the kb to mb range. However, if root is used, then accounting isn't done, and then it's possible to hit this issue.

References

• https://git.kernel.org/stable/c/c6a2706e08b8a1b2d3740161c0977d38e596c1ee
• https://git.kernel.org/stable/c/a69a9b53c54e2d33e2a5b1ea4a9a71fd01c6cf3a
• https://git.kernel.org/stable/c/33503c083fda048c77903460ac0429e1e2c0e341