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 [1] 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 [2]. This can lead to problems because the in-kernel pointer is never checked for validity. If an eBPF syscall program tries to call bpf_sys_bpf() with a bad insns pointer, say 0xdeadbeef (which is supposed to point to the start of the instruction array) in the bpf_attr union, memcpy() is always happy to dereference the bad pointer to cause 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. The same issue in userspace is handled gracefully by copy_from_user(), which would return -EFAULT in such a case. Replace memcpy() with the safer copy_from_kernel_nofault() and strncpy_from_kernel_nofault(). [1]: https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git/tree/include/linux/bpfptr.h [2]: https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git/tree/include/linux/sockptr.h#n44 Signed-off-by: Jinghao Jia <jinghao@xxxxxxxxxxxxx> --- include/linux/sockptr.h | 11 +++-------- 1 file changed, 3 insertions(+), 8 deletions(-) diff --git a/include/linux/sockptr.h b/include/linux/sockptr.h index d45902fb4cad..3b8a41c82516 100644 --- a/include/linux/sockptr.h +++ b/include/linux/sockptr.h @@ -46,8 +46,7 @@ static inline int copy_from_sockptr_offset(void *dst, sockptr_t src, { if (!sockptr_is_kernel(src)) return copy_from_user(dst, src.user + offset, size); - memcpy(dst, src.kernel + offset, size); - return 0; + return copy_from_kernel_nofault(dst, src.kernel + offset, size); } static inline int copy_from_sockptr(void *dst, sockptr_t src, size_t size) @@ -93,12 +92,8 @@ static inline void *memdup_sockptr_nul(sockptr_t src, size_t len) static inline long strncpy_from_sockptr(char *dst, sockptr_t src, size_t count) { - if (sockptr_is_kernel(src)) { - size_t len = min(strnlen(src.kernel, count - 1) + 1, count); - - memcpy(dst, src.kernel, len); - return len; - } + if (sockptr_is_kernel(src)) + return strncpy_from_kernel_nofault(dst, src.kernel, count); return strncpy_from_user(dst, src.user, count); } base-commit: d295daf505758f9a0e4d05f4ee3bfdfb4192c18f -- 2.35.1
