bpf: Refuse unused attributes in bpf_prog_{attach,detach}

The recently added tcx attachment extended the BPF UAPI for attaching and
detaching by a couple of fields. Those fields are currently only supported
for tcx, other types like cgroups and flow dissector silently ignore the
new fields except for the new flags.

This is problematic once we extend bpf_mprog to older attachment types, since
it's hard to figure out whether the syscall really was successful if the
kernel silently ignores non-zero values.

Explicitly reject non-zero fields relevant to bpf_mprog for attachment types
which don't use the latter yet.

Fixes: e420bed02507 ("bpf: Add fd-based tcx multi-prog infra with link support")
Signed-off-by: Lorenz Bauer <lmb@isovalent.com>
Co-developed-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/r/20231006220655.1653-3-daniel@iogearbox.net
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>

diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 453a43695a23baf12301ded40d9f02717cfb4145..d77b2f8b93641b4445645ec2d9397849fe6a5af3 100644 (file)
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -3796,7 +3796,6 @@ static int bpf_prog_attach(const union bpf_attr *attr)
 {
        enum bpf_prog_type ptype;
        struct bpf_prog *prog;
-       u32 mask;
        int ret;
 
        if (CHECK_ATTR(BPF_PROG_ATTACH))
@@ -3805,10 +3804,16 @@ static int bpf_prog_attach(const union bpf_attr *attr)
        ptype = attach_type_to_prog_type(attr->attach_type);
        if (ptype == BPF_PROG_TYPE_UNSPEC)
                return -EINVAL;
-       mask = bpf_mprog_supported(ptype) ?
-              BPF_F_ATTACH_MASK_MPROG : BPF_F_ATTACH_MASK_BASE;
-       if (attr->attach_flags & ~mask)
-               return -EINVAL;
+       if (bpf_mprog_supported(ptype)) {
+               if (attr->attach_flags & ~BPF_F_ATTACH_MASK_MPROG)
+                       return -EINVAL;
+       } else {
+               if (attr->attach_flags & ~BPF_F_ATTACH_MASK_BASE)
+                       return -EINVAL;
+               if (attr->relative_fd ||
+                   attr->expected_revision)
+                       return -EINVAL;
+       }
 
        prog = bpf_prog_get_type(attr->attach_bpf_fd, ptype);
        if (IS_ERR(prog))
@@ -3878,6 +3883,10 @@ static int bpf_prog_detach(const union bpf_attr *attr)
                        if (IS_ERR(prog))
                                return PTR_ERR(prog);
                }
+       } else if (attr->attach_flags ||
+                  attr->relative_fd ||
+                  attr->expected_revision) {
+               return -EINVAL;
        }
 
        switch (ptype) {