CVE-2021-46927 nitro_enclaves: Use get_user_pages_unlocked() call to handle mmap assert
A local attacker can trigger a kernel bug in the Nitro Enclaves driver, causing a system crash and denial of service.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2021-46927?
CVE-2021-46927 is a medium-severity denial of service vulnerability in Linux kernel, published on 27 Feb 2024. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
nitro_enclaves: Use get_user_pages_unlocked() call to handle mmap assert
After commit 5b78ed24e8ec ("mm/pagemap: add mmap_assert_locked() annotations to find_vma*()"), the call to get_user_pages() will trigger the mmap assert.
static inline void mmap_assert_locked(struct mm_struct *mm) { lockdep_assert_held(&mm->mmap_lock); VM_BUG_ON_MM(!rwsem_is_locked(&mm->mmap_lock), mm); }
[ 62.521410] kernel BUG at include/linux/mmap_lock.h:156! ........................................................... [ 62.538938] RIP: 0010:find_vma+0x32/0x80 ........................................................... [ 62.605889] Call Trace: [ 62.608502] <TASK> [ 62.610956] ? lock_timer_base+0x61/0x80 [ 62.614106] find_extend_vma+0x19/0x80 [ 62.617195] __get_user_pages+0x9b/0x6a0 [ 62.620356] __gup_longterm_locked+0x42d/0x450 [ 62.623721] ? finish_wait+0x41/0x80 [ 62.626748] ? __kmalloc+0x178/0x2f0 [ 62.629768] ne_set_user_memory_region_ioctl.isra.0+0x225/0x6a0 [nitro_enclaves] [ 62.635776] ne_enclave_ioctl+0x1cf/0x6d7 [nitro_enclaves] [ 62.639541] __x64_sys_ioctl+0x82/0xb0 [ 62.642620] do_syscall_64+0x3b/0x90 [ 62.645642] entry_SYSCALL_64_after_hwframe+0x44/0xae
Use get_user_pages_unlocked() when setting the enclave memory regions. That's a similar pattern as mmap_read_lock() used together with get_user_pages().
Weakness: CWE-667
Which versions are affected by CVE-2021-46927?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2021-46927?
Apply the vendor's patch.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2021-46927 being exploited?
There is no known exploitation of CVE-2021-46927 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as DEBIAN-CVE-2021-46927, GHSA-4f2m-qf8w-84rw, UBUNTU-CVE-2021-46927.