CVE-2024-49861 bpf: Fix helper writes to read-only maps
Attackers can write to read-only BPF maps via specific helpers, bypassing intended immutability restrictions in the Linux kernel.
- 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-2024-49861?
CVE-2024-49861 is a high-severity missing authorization vulnerability in Linux kernel, published on 21 Oct 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:
bpf: Fix helper writes to read-only maps
Lonial found an issue that despite user- and BPF-side frozen BPF map (like in case of .rodata), it was still possible to write into it from a BPF program side through specific helpers having ARG_PTR_TO_{LONG,INT} as arguments.
In check_func_arg() when the argument is as mentioned, the meta->raw_mode is never set. Later, check_helper_mem_access(), under the case of PTR_TO_MAP_VALUE as register base type, it assumes BPF_READ for the subsequent call to check_map_access_type() and given the BPF map is read-only it succeeds.
The helpers really need to be annotated as ARG_PTR_TO_{LONG,INT} | MEM_UNINIT when results are written into them as opposed to read out of them. The latter indicates that it's okay to pass a pointer to uninitialized memory as the memory is written to anyway.
However, ARG_PTR_TO_{LONG,INT} is a special case of ARG_PTR_TO_FIXED_SIZE_MEM just with additional alignment requirement. So it is better to just get rid of the ARG_PTR_TO_{LONG,INT} special cases altogether and reuse the fixed size memory types. For this, add MEM_ALIGNED to additionally ensure alignment given these helpers write directly into the args via *<ptr> = val. The .arg*_size has been initialized reflecting the actual sizeof(*<ptr>).
MEM_ALIGNED can only be used in combination with MEM_FIXED_SIZE annotated argument types, since in !MEM_FIXED_SIZE cases the verifier does not know the buffer size a priori and therefore cannot blindly write *<ptr> = val.
Which versions are affected by CVE-2024-49861?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2024-49861?
Apply the vendor's patch.
Upgrade, and check permissions on every request on the server, not only in the interface. More about Missing authorization.
Is CVE-2024-49861 being exploited?
There is no known exploitation of CVE-2024-49861 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as AZL-50802, AZL-50858, BELL-CVE-2024-49861, DEBIAN-CVE-2024-49861, GHSA-vf64-qg5h-qxhf, ROOT-OS-DEBIAN-11-CVE-2024-49861 and 2 more.