CVE-2024-36943

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

fs/proc/task_mmu: fix loss of young/dirty bits during pagemap scan

makeuffdwp_pte() was previously doing:

pte = ptepget(ptep); ptepmodifyprotstart(ptep); pte = ptemkuffdwp(pte); ptepmodifyprot_commit(ptep, pte);

But if another thread accessed or dirtied the pte between the first 2 calls, this could lead to loss of that information. Since ptepmodifyprot_start() gets and clears atomically, the following is the correct pattern and prevents any possible race. Any access after the first call would see an invalid pte and cause a fault:

pte = ptepmodifyprotstart(ptep); pte = ptemkuffdwp(pte); ptepmodifyprotcommit(ptep, pte);