[RFC PATCH bpf-next seccomp 10/12] seccomp-ebpf: Add ability to read user memory
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STALE1967d
From: YiFei Zhu <hidden>
Date: 2021-05-10 17:23:42
Also in:
bpf
Subsystem:
bpf [core], bpf [general] (safe dynamic programs and tools), bpf [security & lsm] (security audit and enforcement using bpf), bpf [tracing], secure computing, the rest, tracing · Maintainers:
Alexei Starovoitov, Daniel Borkmann, Andrii Nakryiko, Eduard Zingerman, Kumar Kartikeya Dwivedi, KP Singh, Matt Bobrowski, Song Liu, Kees Cook, Linus Torvalds, Steven Rostedt, Masami Hiramatsu
From: YiFei Zhu <redacted>
This uses helpers bpf_probe_read_user{,str}. To repect unprivileged
users may also load filters, when the loader of the filter does not
have CAP_SYS_PTRACE, attempting to read user memory when current mm
is non-dumpable results in -EPERM.
Right now this is not sleepable, -EFAULT may happen for valid memory
addresses. Future work might be adding support to bpf_copy_from_user
via sleepable filters.
Use of memory data to implement policy is discouraged until there is
a solution for time-of-check to time-of-use.
Signed-off-by: YiFei Zhu <redacted>
---
include/linux/bpf.h | 4 ++++
kernel/seccomp.c | 8 ++++++++
kernel/trace/bpf_trace.c | 42 ++++++++++++++++++++++++++++++++++++++++
3 files changed, 54 insertions(+)
diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 86f3e8784e43..2019c0893250 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h@@ -1965,6 +1965,10 @@ extern const struct bpf_func_proto bpf_get_socket_ptr_cookie_proto; extern const struct bpf_func_proto bpf_task_storage_get_proto; extern const struct bpf_func_proto bpf_task_storage_delete_proto; extern const struct bpf_func_proto bpf_for_each_map_elem_proto; +extern const struct bpf_func_proto bpf_probe_read_user_proto; +extern const struct bpf_func_proto bpf_probe_read_user_dumpable_proto; +extern const struct bpf_func_proto bpf_probe_read_user_str_proto; +extern const struct bpf_func_proto bpf_probe_read_user_dumpable_str_proto; const struct bpf_func_proto *bpf_tracing_func_proto( enum bpf_func_id func_id, const struct bpf_prog *prog);
diff --git a/kernel/seccomp.c b/kernel/seccomp.c
index b9ed9951a05b..330e9c365cdc 100644
--- a/kernel/seccomp.c
+++ b/kernel/seccomp.c@@ -2449,6 +2449,14 @@ seccomp_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog) return &bpf_get_current_uid_gid_proto; case BPF_FUNC_get_current_pid_tgid: return &bpf_get_current_pid_tgid_proto; + case BPF_FUNC_probe_read_user: + return ns_capable(current_user_ns(), CAP_SYS_PTRACE) ? + &bpf_probe_read_user_proto : + &bpf_probe_read_user_dumpable_proto; + case BPF_FUNC_probe_read_user_str: + return ns_capable(current_user_ns(), CAP_SYS_PTRACE) ? + &bpf_probe_read_user_str_proto : + &bpf_probe_read_user_dumpable_str_proto; default: break; }
diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index d2d7cf6cfe83..a1d6d64bde08 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c@@ -175,6 +175,27 @@ const struct bpf_func_proto bpf_probe_read_user_proto = { .arg3_type = ARG_ANYTHING, }; +BPF_CALL_3(bpf_probe_read_user_dumpable, void *, dst, u32, size, + const void __user *, unsafe_ptr) +{ + int ret = -EPERM; + + if (get_dumpable(current->mm)) + ret = copy_from_user_nofault(dst, unsafe_ptr, size); + if (unlikely(ret < 0)) + memset(dst, 0, size); + return ret; +} + +const struct bpf_func_proto bpf_probe_read_user_dumpable_proto = { + .func = bpf_probe_read_user_dumpable, + .gpl_only = true, + .ret_type = RET_INTEGER, + .arg1_type = ARG_PTR_TO_UNINIT_MEM, + .arg2_type = ARG_CONST_SIZE_OR_ZERO, + .arg3_type = ARG_ANYTHING, +}; + static __always_inline int bpf_probe_read_user_str_common(void *dst, u32 size, const void __user *unsafe_ptr)
@@ -212,6 +233,27 @@ const struct bpf_func_proto bpf_probe_read_user_str_proto = { .arg3_type = ARG_ANYTHING, }; +BPF_CALL_3(bpf_probe_read_user_dumpable_str, void *, dst, u32, size, + const void __user *, unsafe_ptr) +{ + int ret = -EPERM; + + if (get_dumpable(current->mm)) + ret = strncpy_from_user_nofault(dst, unsafe_ptr, size); + if (unlikely(ret < 0)) + memset(dst, 0, size); + return ret; +} + +const struct bpf_func_proto bpf_probe_read_user_dumpable_str_proto = { + .func = bpf_probe_read_user_dumpable_str, + .gpl_only = true, + .ret_type = RET_INTEGER, + .arg1_type = ARG_PTR_TO_UNINIT_MEM, + .arg2_type = ARG_CONST_SIZE_OR_ZERO, + .arg3_type = ARG_ANYTHING, +}; + static __always_inline int bpf_probe_read_kernel_common(void *dst, u32 size, const void *unsafe_ptr) {
--
2.31.1