bpf: Add validation for bpf_set_retval argument

The bpf_set_retval() helper is used by cgroup BPF programs to set the
return value of the target hook. The argument type for this helper is
ARG_ANYTHING. This allows setting a positive value, which no cgroup
hook expects and can cause issues, such as:

- BPF_LSM_CGROUP: a positive value from bpf_lsm_socket_create bypasses
  the err < 0 check in __sock_create(), leaving the socket object
  unallocated. The positive return value is then propagated to the
  syscall entry __sys_socket(), which also bypasses the IS_ERR() guard
  and ultimately causes a NULL pointer dereference.

- BPF_CGROUP_DEVICE: a positive value can be returned through cgroup
  device bpf prog -> devcgroup_check_permission() -> bdev_permission()
  -> bdev_file_open_by_dev(), where ERR_PTR(positive) produces a pointer
  that IS_ERR() does not catch, leading to a wild pointer dereference.

- BPF_CGROUP_SOCK: a positive value can be returned through cgroup sock
  bpf prog -> __cgroup_bpf_run_filter_sk() -> inet_create() ->
  __sock_create(), where inet_create() frees the newly allocated sk
  via sk_common_release() and sets sock->sk = NULL on the non-zero
  return, but __sock_create() only checks err < 0 for cleanup, so a
  positive retval bypasses cleanup and returns a socket with NULL sk
  to userspace, triggering a NULL pointer dereference on subsequent
  socket operations.

- BPF_CGROUP_SYSCTL: a positive value can be returned through the cgroup
  bpf prog -> __cgroup_bpf_run_filter_sysctl() -> proc_sys_call_handler(),
  where a non-zero return bypasses the normal sysctl proc_handler and is
  returned directly to userspace as return value of read() or write()
  syscall.

So add validation for the argument of the bpf_set_retval() helper.

For BPF_LSM_CGROUP, enforce the LSM hook specific range returned by
bpf_lsm_get_retval_range().

For all other cgroup program types, restrict the argument to
[-MAX_ERRNO, 0], which matches the kernel convention of 0 for success
and negative errno for error.

BPF_CGROUP_GETSOCKOPT is an exception, since valid getsockopt
implementations may return positive values, as allowed by commit
c4dcfdd406aa ("bpf: Move getsockopt retval to struct bpf_cg_run_ctx").

Also refine the return value range of bpf_get_retval() so that
values returned by bpf_get_retval() can be passed directly to
bpf_set_retval() without extra manual bounds checking.

Fixes: b44123b4a3dc ("bpf: Add cgroup helpers bpf_{get,set}_retval to get/set syscall return value")
Fixes: 69fd337a975c ("bpf: per-cgroup lsm flavor")
Reported-by: Quan Sun <2022090917019@std.uestc.edu.cn>
Closes: https://lore.kernel.org/all/567d3206-74a5-44e5-99c6-779c425f399e@std.uestc.edu.cn
Signed-off-by: Xu Kuohai <xukuohai@huawei.com>
Link: https://lore.kernel.org/r/20260605140243.664590-3-xukuohai@huaweicloud.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

0 files changed, 0 insertions, 0 deletions