CVE-2024-49861

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.