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Wed, 12 Aug 2026 11:42:45 -0700 (PDT) Date: Wed, 12 Aug 2026 14:42:44 -0400 From: Justin Suess To: Anastasios Papagiannis Cc: bpf@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, viro@zeniv.linux.org.uk, brauner@kernel.org, akpm@linux-foundation.org, david@kernel.org, ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org, eddyz87@gmail.com, memxor@gmail.com, kpsingh@kernel.org, matt@bobrowski.net, song@kernel.org Subject: Re: [PATCH bpf-next 3/3] selftests/bpf: Test linux_binprm user memory kfuncs Message-ID: References: <20260812111140.7762-1-tasos.papagiannnis@gmail.com> <20260812111140.7762-4-tasos.papagiannnis@gmail.com> Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260812111140.7762-4-tasos.papagiannnis@gmail.com> On Wed, Aug 12, 2026 at 02:11:40PM +0300, Anastasios Papagiannis wrote: > This patch adds a sleepable BPF LSM program attached to > bprm_check_security to test bpf_copy_from_user_bprm() and > bpf_copy_from_user_bprm_str(). > > Starting at bprm->p, verify that bpf_copy_from_user_bprm() can copy the > contiguous NUL-separated argument data. Then use > bpf_copy_from_user_bprm_str() to read each argument separately, > by advancing the offset based on the returned length. > Can you test reading environment strings as well? It would be nice to have an example on how to do that. Justin > Signed-off-by: Anastasios Papagiannis > --- > .../bpf/prog_tests/copy_from_user_bprm.c | 52 +++++++++++++ > .../selftests/bpf/progs/copy_from_user_bprm.c | 74 +++++++++++++++++++ > 2 files changed, 126 insertions(+) > create mode 100644 tools/testing/selftests/bpf/prog_tests/copy_from_user_bprm.c > create mode 100644 tools/testing/selftests/bpf/progs/copy_from_user_bprm.c > > diff --git a/tools/testing/selftests/bpf/prog_tests/copy_from_user_bprm.c b/tools/testing/selftests/bpf/prog_tests/copy_from_user_bprm.c > new file mode 100644 > index 000000000000..3d5080a3975e > --- /dev/null > +++ b/tools/testing/selftests/bpf/prog_tests/copy_from_user_bprm.c > @@ -0,0 +1,52 @@ > +// SPDX-License-Identifier: GPL-2.0 > + > +#include > +#include > +#include > + > +#include > + > +#include "copy_from_user_bprm.skel.h" > + > +void test_copy_from_user_bprm(void) > +{ > + struct copy_from_user_bprm *skel; > + pid_t child; > + int status; > + > + skel = copy_from_user_bprm__open_and_load(); > + if (!ASSERT_OK_PTR(skel, "open_and_load")) > + return; > + > + if (!ASSERT_OK(copy_from_user_bprm__attach(skel), "attach")) > + goto out; > + > + child = fork(); > + if (!ASSERT_GE(child, 0, "fork")) > + goto out; > + > + if (!child) { > + char *const argv[] = { "first", "second-argument", NULL }; > + > + skel->bss->monitored_pid = getpid(); > + execv("/bin/true", argv); > + _exit(errno); > + } > + > + if (!ASSERT_EQ(waitpid(child, &status, 0), child, "waitpid")) > + goto out; > + > + if (ASSERT_TRUE(WIFEXITED(status), "child_exited")) > + ASSERT_EQ(WEXITSTATUS(status), EPERM, "exec_errno"); > + > + ASSERT_EQ(skel->bss->bprm_argc, 2, "bprm_argc"); > + ASSERT_EQ(skel->bss->invalid_flags_ret, -EINVAL, "invalid_flags_ret"); > + ASSERT_EQ(skel->bss->copy_ret, 0, "copy_ret"); > + ASSERT_EQ(skel->bss->str_arg0_ret, 6, "str_arg0_ret"); > + ASSERT_EQ(skel->bss->str_arg1_ret, 16, "str_arg1_ret"); > + ASSERT_EQ(skel->bss->args_match, 1, "args_match"); > + ASSERT_EQ(skel->bss->str_args_match, 1, "str_args_match"); > + > +out: > + copy_from_user_bprm__destroy(skel); > +} > diff --git a/tools/testing/selftests/bpf/progs/copy_from_user_bprm.c b/tools/testing/selftests/bpf/progs/copy_from_user_bprm.c > new file mode 100644 > index 000000000000..679363811edc > --- /dev/null > +++ b/tools/testing/selftests/bpf/progs/copy_from_user_bprm.c > @@ -0,0 +1,74 @@ > +// SPDX-License-Identifier: GPL-2.0 > + > +#include "vmlinux.h" > + > +#include > +#include > +#include > +#include "bpf_misc.h" > + > +char _license[] SEC("license") = "GPL"; > + > +static const char expected_args[] = "first\0second-argument"; > +static const char expected_arg0[] = "first"; > +static const char expected_arg1[] = "second-argument"; > + > +int monitored_pid; > +int bprm_argc; > +int invalid_flags_ret; > +int copy_ret; > +int str_arg0_ret; > +int str_arg1_ret; > +int args_match; > +int str_args_match; > + > +extern int bpf_copy_from_user_bprm(void *dst, u32 dst__sz, > + const void *unsafe_ptr__ign, > + const struct linux_binprm *bprm, > + u64 flags) __ksym; > + > +extern int bpf_copy_from_user_bprm_str(void *dst, u32 dst__sz, > + const void *unsafe_ptr__ign, > + const struct linux_binprm *bprm, > + u64 flags) __ksym; > + > +SEC("lsm.s/bprm_check_security") > +int BPF_PROG(check_exec_args, struct linux_binprm *bprm, int ret) > +{ > + u32 pid = bpf_get_current_pid_tgid() >> 32; > + char args[sizeof(expected_args)]; > + char arg0[32]; > + char arg1[32]; > + > + if (ret || pid != monitored_pid) > + return ret; > + > + bprm_argc = bprm->argc; > + > + invalid_flags_ret = bpf_copy_from_user_bprm(args, sizeof(args), > + (void *)bprm->p, bprm, 1); > + > + copy_ret = bpf_copy_from_user_bprm(args, sizeof(args), > + (void *)bprm->p, bprm, 0); > + if (copy_ret) > + return 0; > + > + args_match = !__builtin_memcmp(args, expected_args, sizeof(expected_args)); > + > + str_arg0_ret = bpf_copy_from_user_bprm_str(arg0, sizeof(arg0), > + (void *)bprm->p, bprm, > + BPF_F_PAD_ZEROS); > + if (str_arg0_ret != sizeof(expected_arg0)) > + return 0; > + > + str_arg1_ret = bpf_copy_from_user_bprm_str(arg1, sizeof(arg1), > + (void *)(bprm->p + str_arg0_ret), > + bprm, BPF_F_PAD_ZEROS); > + if (str_arg1_ret != sizeof(expected_arg1)) > + return 0; > + > + str_args_match = !__builtin_memcmp(arg0, expected_arg0, sizeof(expected_arg0)) && > + !__builtin_memcmp(arg1, expected_arg1, sizeof(expected_arg1)); > + > + return args_match && str_args_match ? -EPERM : 0; > +} > -- > 2.55.0 >