2025-06-18 11:02:14
Linux
PUBLISHED
In the Linux kernel, the following vulnerability has been resolved:
BPF: Fix potential bad pointer dereference in bpf_sys_bpf()
The bpf_sys_bpf() helper function allows an eBPF program to load another
eBPF program from within the kernel. In this case the argument union
bpf_attr pointer (as well as the insns and license pointers inside) is a
kernel address instead of a userspace address (which is the case of a
usual bpf() syscall). To make the memory copying process in the syscall
work in both cases, bpfptr_t was introduced to wrap around the pointer
and distinguish its origin. Specifically, when copying memory contents
from a bpfptr_t, a copy_from_user() is performed in case of a userspace
address and a memcpy() is performed for a kernel address.
This can lead to problems because the in-kernel pointer is never checked
for validity. The problem happens when an eBPF syscall program tries to
call bpf_sys_bpf() to load a program but provides a bad insns pointer --
say 0xdeadbeef -- in the bpf_attr union. The helper calls __sys_bpf()
which would then call bpf_prog_load() to load the program.
bpf_prog_load() is responsible for copying the eBPF instructions to the
newly allocated memory for the program; it creates a kernel bpfptr_t for
insns and invokes copy_from_bpfptr(). Internally, all bpfptr_t
operations are backed by the corresponding sockptr_t operations, which
performs direct memcpy() on kernel pointers for copy_from/strncpy_from
operations. Therefore, the code is always happy to dereference the bad
pointer to trigger a un-handle-able page fault and in turn an oops.
However, this is not supposed to happen because at that point the eBPF
program is already verified and should not cause a memory error.
Sample KASAN trace:
[ 25.685056][ T228] ==================================================================
[ 25.685680][ T228] BUG: KASAN: user-memory-access in copy_from_bpfptr+0x21/0x30
[ 25.686210][ T228] Read of size 80 at addr 00000000deadbeef by task poc/228
[ 25.686732][ T228]
[ 25.686893][ T228] CPU: 3 PID: 228 Comm: poc Not tainted 5.19.0-rc7 #7
[ 25.687375][ T228] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS d55cb5a 04/01/2014
[ 25.687991][ T228] Call Trace:
[ 25.688223][ T228]