From 2a040f9f39d3b020c79e08dec26d12a7ce131c10 Mon Sep 17 00:00:00 2001 From: Tycho Andersen Date: Tue, 20 Feb 2018 19:47:45 -0700 Subject: [PATCH 1/3] seccomp, ptrace: switch get_metadata types to arch independent Commit 26500475ac1b ("ptrace, seccomp: add support for retrieving seccomp metadata") introduced `struct seccomp_metadata`, which contained unsigned longs that should be arch independent. The type of the flags member was chosen to match the corresponding argument to seccomp(), and so we need something at least as big as unsigned long. My understanding is that __u64 should fit the bill, so let's switch both types to that. While this is userspace facing, it was only introduced in 4.16-rc2, and so should be safe assuming it goes in before then. Reported-by: "Dmitry V. Levin" Signed-off-by: Tycho Andersen CC: Kees Cook CC: Oleg Nesterov Reviewed-by: "Dmitry V. Levin" Signed-off-by: Kees Cook --- include/uapi/linux/ptrace.h | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/include/uapi/linux/ptrace.h b/include/uapi/linux/ptrace.h index e46d82b91166..d5a1b8a492b9 100644 --- a/include/uapi/linux/ptrace.h +++ b/include/uapi/linux/ptrace.h @@ -69,8 +69,8 @@ struct ptrace_peeksiginfo_args { #define PTRACE_SECCOMP_GET_METADATA 0x420d struct seccomp_metadata { - unsigned long filter_off; /* Input: which filter */ - unsigned int flags; /* Output: filter's flags */ + __u64 filter_off; /* Input: which filter */ + __u64 flags; /* Output: filter's flags */ }; /* Read signals from a shared (process wide) queue */ From 63bb0045b98ae821e56e27c2250e14bb0ae663e5 Mon Sep 17 00:00:00 2001 From: Tycho Andersen Date: Tue, 20 Feb 2018 19:47:46 -0700 Subject: [PATCH 2/3] ptrace, seccomp: tweak get_metadata behavior slightly Previously if users passed a small size for the input structure size, they would get get odd behavior. It doesn't make sense to pass a structure smaller than at least filter_off size, so let's just give -EINVAL in this case. This changes userspace visible behavior, but was only introduced in commit 26500475ac1b ("ptrace, seccomp: add support for retrieving seccomp metadata") in 4.16-rc2, so should be safe to change if merged before then. Reported-by: Eugene Syromiatnikov Signed-off-by: Tycho Andersen CC: Kees Cook CC: Oleg Nesterov Signed-off-by: Kees Cook --- kernel/seccomp.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/kernel/seccomp.c b/kernel/seccomp.c index 61bd9dc260c8..1245b2338fff 100644 --- a/kernel/seccomp.c +++ b/kernel/seccomp.c @@ -1076,14 +1076,16 @@ long seccomp_get_metadata(struct task_struct *task, size = min_t(unsigned long, size, sizeof(kmd)); - if (copy_from_user(&kmd, data, size)) + if (size < sizeof(kmd.filter_off)) + return -EINVAL; + + if (copy_from_user(&kmd.filter_off, data, sizeof(kmd.filter_off))) return -EFAULT; filter = get_nth_filter(task, kmd.filter_off); if (IS_ERR(filter)) return PTR_ERR(filter); - memset(&kmd, 0, sizeof(kmd)); if (filter->log) kmd.flags |= SECCOMP_FILTER_FLAG_LOG; From d057dc4e35e16050befa3dda943876dab39cbf80 Mon Sep 17 00:00:00 2001 From: Tycho Andersen Date: Tue, 20 Feb 2018 19:47:47 -0700 Subject: [PATCH 3/3] seccomp: add a selftest for get_metadata Let's test that we get the flags correctly, and that we preserve the filter index across the ptrace(PTRACE_SECCOMP_GET_METADATA) correctly. Signed-off-by: Tycho Andersen CC: Kees Cook Signed-off-by: Kees Cook --- tools/testing/selftests/seccomp/seccomp_bpf.c | 61 +++++++++++++++++++ 1 file changed, 61 insertions(+) diff --git a/tools/testing/selftests/seccomp/seccomp_bpf.c b/tools/testing/selftests/seccomp/seccomp_bpf.c index 24dbf634e2dd..92db48825dc1 100644 --- a/tools/testing/selftests/seccomp/seccomp_bpf.c +++ b/tools/testing/selftests/seccomp/seccomp_bpf.c @@ -141,6 +141,15 @@ struct seccomp_data { #define SECCOMP_FILTER_FLAG_LOG 2 #endif +#ifndef PTRACE_SECCOMP_GET_METADATA +#define PTRACE_SECCOMP_GET_METADATA 0x420d + +struct seccomp_metadata { + __u64 filter_off; /* Input: which filter */ + __u64 flags; /* Output: filter's flags */ +}; +#endif + #ifndef seccomp int seccomp(unsigned int op, unsigned int flags, void *args) { @@ -2845,6 +2854,58 @@ TEST(get_action_avail) EXPECT_EQ(errno, EOPNOTSUPP); } +TEST(get_metadata) +{ + pid_t pid; + int pipefd[2]; + char buf; + struct seccomp_metadata md; + + ASSERT_EQ(0, pipe(pipefd)); + + pid = fork(); + ASSERT_GE(pid, 0); + if (pid == 0) { + struct sock_filter filter[] = { + BPF_STMT(BPF_RET|BPF_K, SECCOMP_RET_ALLOW), + }; + struct sock_fprog prog = { + .len = (unsigned short)ARRAY_SIZE(filter), + .filter = filter, + }; + + /* one with log, one without */ + ASSERT_EQ(0, seccomp(SECCOMP_SET_MODE_FILTER, + SECCOMP_FILTER_FLAG_LOG, &prog)); + ASSERT_EQ(0, seccomp(SECCOMP_SET_MODE_FILTER, 0, &prog)); + + ASSERT_EQ(0, close(pipefd[0])); + ASSERT_EQ(1, write(pipefd[1], "1", 1)); + ASSERT_EQ(0, close(pipefd[1])); + + while (1) + sleep(100); + } + + ASSERT_EQ(0, close(pipefd[1])); + ASSERT_EQ(1, read(pipefd[0], &buf, 1)); + + ASSERT_EQ(0, ptrace(PTRACE_ATTACH, pid)); + ASSERT_EQ(pid, waitpid(pid, NULL, 0)); + + md.filter_off = 0; + ASSERT_EQ(sizeof(md), ptrace(PTRACE_SECCOMP_GET_METADATA, pid, sizeof(md), &md)); + EXPECT_EQ(md.flags, SECCOMP_FILTER_FLAG_LOG); + EXPECT_EQ(md.filter_off, 0); + + md.filter_off = 1; + ASSERT_EQ(sizeof(md), ptrace(PTRACE_SECCOMP_GET_METADATA, pid, sizeof(md), &md)); + EXPECT_EQ(md.flags, 0); + EXPECT_EQ(md.filter_off, 1); + + ASSERT_EQ(0, kill(pid, SIGKILL)); +} + /* * TODO: * - add microbenchmarks