| Message ID | 20170807163605.14194-2-mic@digikod.net |
|---|---|
| State | Changes Requested, archived |
| Delegated to: | David Miller |
| Headers | show |
On 08/07/2017 06:36 PM, Mickaël Salaün wrote: > The function check_uarg_tail_zero() was created from bpf(2) for > BPF_OBJ_GET_INFO_BY_FD without taking the access_ok() nor the PAGE_SIZE > checks. Make this checks more generally available while unlikely to be > triggered, extend the memory range check and add an explanation > including why the ToCToU should not be a security concern. > > Signed-off-by: Mickaël Salaün <mic@digikod.net> > Cc: Alexei Starovoitov <ast@kernel.org> > Cc: Daniel Borkmann <daniel@iogearbox.net> > Cc: David S. Miller <davem@davemloft.net> > Cc: Kees Cook <keescook@chromium.org> > Cc: Martin KaFai Lau <kafai@fb.com> > Link: https://lkml.kernel.org/r/CAGXu5j+vRGFvJZmjtAcT8Hi8B+Wz0e1b6VKYZHfQP_=DXzC4CQ@mail.gmail.com > --- > kernel/bpf/syscall.c | 26 +++++++++++++++----------- > 1 file changed, 15 insertions(+), 11 deletions(-) > > diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c > index c653ee0bd162..b884fdc371e0 100644 > --- a/kernel/bpf/syscall.c > +++ b/kernel/bpf/syscall.c > @@ -48,6 +48,15 @@ static const struct bpf_map_ops * const bpf_map_types[] = { > #undef BPF_MAP_TYPE > }; > > +/* > + * If we're handed a bigger struct than we know of, ensure all the unknown bits > + * are 0 - i.e. new user-space does not rely on any kernel feature extensions > + * we dont know about yet. Nit: don't > + * > + * There is a ToCToU between this function call and the following > + * copy_from_user() call. However, this should not be a concern since this Lets make it a bit more clear to the reader: s/should not/is not/ > + * function is meant to be a future-proofing of bits. > + */ > static int check_uarg_tail_zero(void __user *uaddr, > size_t expected_size, > size_t actual_size) > @@ -57,6 +66,12 @@ static int check_uarg_tail_zero(void __user *uaddr, > unsigned char val; > int err; > > + if (unlikely(!access_ok(VERIFY_READ, uaddr, actual_size))) > + return -EFAULT; > + > + if (unlikely(actual_size > PAGE_SIZE)) /* silly large */ > + return -E2BIG; > + Yeah, moving the checks into check_uarg_tail_zero() is fine by me. Can we make the 'silly large' test first, so we don't generate unnecessary work if we bail out later anyway? Other than that: Acked-by: Daniel Borkmann <daniel@iogearbox.net> Thanks, Daniel > if (actual_size <= expected_size) > return 0; > > @@ -1393,17 +1408,6 @@ SYSCALL_DEFINE3(bpf, int, cmd, union bpf_attr __user *, uattr, unsigned int, siz > if (!capable(CAP_SYS_ADMIN) && sysctl_unprivileged_bpf_disabled) > return -EPERM; > > - if (!access_ok(VERIFY_READ, uattr, 1)) > - return -EFAULT; > - > - if (size > PAGE_SIZE) /* silly large */ > - return -E2BIG; > - > - /* If we're handed a bigger struct than we know of, > - * ensure all the unknown bits are 0 - i.e. new > - * user-space does not rely on any kernel feature > - * extensions we dont know about yet. > - */ > err = check_uarg_tail_zero(uattr, sizeof(attr), size); > if (err) > return err; >
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c index c653ee0bd162..b884fdc371e0 100644 --- a/kernel/bpf/syscall.c +++ b/kernel/bpf/syscall.c @@ -48,6 +48,15 @@ static const struct bpf_map_ops * const bpf_map_types[] = { #undef BPF_MAP_TYPE }; +/* + * If we're handed a bigger struct than we know of, ensure all the unknown bits + * are 0 - i.e. new user-space does not rely on any kernel feature extensions + * we dont know about yet. + * + * There is a ToCToU between this function call and the following + * copy_from_user() call. However, this should not be a concern since this + * function is meant to be a future-proofing of bits. + */ static int check_uarg_tail_zero(void __user *uaddr, size_t expected_size, size_t actual_size) @@ -57,6 +66,12 @@ static int check_uarg_tail_zero(void __user *uaddr, unsigned char val; int err; + if (unlikely(!access_ok(VERIFY_READ, uaddr, actual_size))) + return -EFAULT; + + if (unlikely(actual_size > PAGE_SIZE)) /* silly large */ + return -E2BIG; + if (actual_size <= expected_size) return 0; @@ -1393,17 +1408,6 @@ SYSCALL_DEFINE3(bpf, int, cmd, union bpf_attr __user *, uattr, unsigned int, siz if (!capable(CAP_SYS_ADMIN) && sysctl_unprivileged_bpf_disabled) return -EPERM; - if (!access_ok(VERIFY_READ, uattr, 1)) - return -EFAULT; - - if (size > PAGE_SIZE) /* silly large */ - return -E2BIG; - - /* If we're handed a bigger struct than we know of, - * ensure all the unknown bits are 0 - i.e. new - * user-space does not rely on any kernel feature - * extensions we dont know about yet. - */ err = check_uarg_tail_zero(uattr, sizeof(attr), size); if (err) return err;
The function check_uarg_tail_zero() was created from bpf(2) for BPF_OBJ_GET_INFO_BY_FD without taking the access_ok() nor the PAGE_SIZE checks. Make this checks more generally available while unlikely to be triggered, extend the memory range check and add an explanation including why the ToCToU should not be a security concern. Signed-off-by: Mickaël Salaün <mic@digikod.net> Cc: Alexei Starovoitov <ast@kernel.org> Cc: Daniel Borkmann <daniel@iogearbox.net> Cc: David S. Miller <davem@davemloft.net> Cc: Kees Cook <keescook@chromium.org> Cc: Martin KaFai Lau <kafai@fb.com> Link: https://lkml.kernel.org/r/CAGXu5j+vRGFvJZmjtAcT8Hi8B+Wz0e1b6VKYZHfQP_=DXzC4CQ@mail.gmail.com --- kernel/bpf/syscall.c | 26 +++++++++++++++----------- 1 file changed, 15 insertions(+), 11 deletions(-)