| Message ID | 20211115165227.101124-1-andrea.righi@canonical.com (mailing list archive) |
|---|---|
| State | Not Applicable |
| Delegated to: | BPF |
| Headers | show |
| Series | selftests/seccomp: fix check of fds being assigned | expand |
| Context | Check | Description |
|---|---|---|
| netdev/tree_selection | success | Not a local patch |
On Mon, Nov 15, 2021 at 05:52:27PM +0100, Andrea Righi wrote: > There might be an arbitrary free open fd slot when we run the addfd > sub-test, so checking for progressive numbers of file descriptors > starting from memfd is not always a reliable check and we could get the > following failure: > > # RUN global.user_notification_addfd ... > # seccomp_bpf.c:3989:user_notification_addfd:Expected listener (18) == nextfd++ (9) > # user_notification_addfd: Test terminated by assertion > > Simply check if memfd and listener are valid file descriptors and start > counting for progressive file checking with the listener fd. > > Fixes: 93e720d710df ("selftests/seccomp: More closely track fds being assigned") > Signed-off-by: Andrea Righi <andrea.righi@canonical.com> > --- Thanks! Acked-by: Christian Brauner <christian.brauner@ubuntu.com>
On Mon, Nov 15, 2021 at 05:52:27PM +0100, Andrea Righi wrote: > There might be an arbitrary free open fd slot when we run the addfd > sub-test, so checking for progressive numbers of file descriptors > starting from memfd is not always a reliable check and we could get the > following failure: > > # RUN global.user_notification_addfd ... > # seccomp_bpf.c:3989:user_notification_addfd:Expected listener (18) == nextfd++ (9) What injected 9 extra fds into this test? > # user_notification_addfd: Test terminated by assertion > > Simply check if memfd and listener are valid file descriptors and start > counting for progressive file checking with the listener fd. Hm, so I attempted to fix this once already: 93e720d710df ("selftests/seccomp: More closely track fds being assigned") so I'm not sure the proposed patch really improves it in the general case. > Fixes: 93e720d710df ("selftests/seccomp: More closely track fds being assigned") > Signed-off-by: Andrea Righi <andrea.righi@canonical.com> > --- > tools/testing/selftests/seccomp/seccomp_bpf.c | 5 ++--- > 1 file changed, 2 insertions(+), 3 deletions(-) > > diff --git a/tools/testing/selftests/seccomp/seccomp_bpf.c b/tools/testing/selftests/seccomp/seccomp_bpf.c > index d425688cf59c..4f37153378a1 100644 > --- a/tools/testing/selftests/seccomp/seccomp_bpf.c > +++ b/tools/testing/selftests/seccomp/seccomp_bpf.c > @@ -3975,18 +3975,17 @@ TEST(user_notification_addfd) > /* There may be arbitrary already-open fds at test start. */ > memfd = memfd_create("test", 0); > ASSERT_GE(memfd, 0); > - nextfd = memfd + 1; > > ret = prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0); > ASSERT_EQ(0, ret) { > TH_LOG("Kernel does not support PR_SET_NO_NEW_PRIVS!"); > } > > - /* fd: 4 */ > /* Check that the basic notification machinery works */ > listener = user_notif_syscall(__NR_getppid, > SECCOMP_FILTER_FLAG_NEW_LISTENER); > - ASSERT_EQ(listener, nextfd++); > + ASSERT_GE(listener, 0); > + nextfd = listener + 1; e.g. if there was a hole in the fd map for memfd, why not listener too? Should the test dup2 memfd up to fd 100 and start counting there or something? What is the condition that fills the fds for this process? -Kees > > pid = fork(); > ASSERT_GE(pid, 0); > -- > 2.32.0 >
On Thu, Nov 18, 2021 at 09:37:03AM -0800, Kees Cook wrote: > On Mon, Nov 15, 2021 at 05:52:27PM +0100, Andrea Righi wrote: > > There might be an arbitrary free open fd slot when we run the addfd > > sub-test, so checking for progressive numbers of file descriptors > > starting from memfd is not always a reliable check and we could get the > > following failure: > > > > # RUN global.user_notification_addfd ... > > # seccomp_bpf.c:3989:user_notification_addfd:Expected listener (18) == nextfd++ (9) > > What injected 9 extra fds into this test? > We run the kselftest inside a framework (bash/python scripts basically) and this is what I see (I added a simple `ls -l /proc/pid/fd` in seccomp_bpf.c after memfd is created): 11/26 08:50:08 DEBUG| utils:0153| [stdout] # # RUN global.user_notification_addfd ... 11/26 08:50:08 DEBUG| utils:0153| [stdout] # total 0 11/26 08:50:08 DEBUG| utils:0153| [stdout] # lrwx------ 1 root root 64 Nov 26 08:50 0 -> /dev/pts/0 11/26 08:50:08 DEBUG| utils:0153| [stdout] # l-wx------ 1 root root 64 Nov 26 08:50 1 -> pipe:[28844] 11/26 08:50:08 DEBUG| utils:0153| [stdout] # lrwx------ 1 root root 64 Nov 26 08:50 10 -> /dev/pts/0 11/26 08:50:08 DEBUG| utils:0153| [stdout] # lrwx------ 1 root root 64 Nov 26 08:50 11 -> /dev/pts/0 11/26 08:50:08 DEBUG| utils:0153| [stdout] # l-wx------ 1 root root 64 Nov 26 08:50 12 -> /home/ubuntu/autotest/client/results/default/ubuntu_kernel_selftests.seccomp:seccomp_bpf/debug/ubuntu_kernel_selftests.seccomp:seccomp_bpf.DEBUG 11/26 08:50:08 DEBUG| utils:0153| [stdout] # l-wx------ 1 root root 64 Nov 26 08:50 13 -> /home/ubuntu/autotest/client/results/default/ubuntu_kernel_selftests.seccomp:seccomp_bpf/debug/ubuntu_kernel_selftests.seccomp:seccomp_bpf.INFO 11/26 08:50:08 DEBUG| utils:0153| [stdout] # l-wx------ 1 root root 64 Nov 26 08:50 14 -> /home/ubuntu/autotest/client/results/default/ubuntu_kernel_selftests.seccomp:seccomp_bpf/debug/ubuntu_kernel_selftests.seccomp:seccomp_bpf.WARNING 11/26 08:50:08 DEBUG| utils:0153| [stdout] # l-wx------ 1 root root 64 Nov 26 08:50 15 -> /home/ubuntu/autotest/client/results/default/ubuntu_kernel_selftests.seccomp:seccomp_bpf/debug/ubuntu_kernel_selftests.seccomp:seccomp_bpf.ERROR 11/26 08:50:08 DEBUG| utils:0153| [stdout] # l-wx------ 1 root root 64 Nov 26 08:50 16 -> pipe:[27608] 11/26 08:50:08 DEBUG| utils:0153| [stdout] # l-wx------ 1 root root 64 Nov 26 08:50 17 -> pipe:[27609] 11/26 08:50:08 DEBUG| utils:0153| [stdout] # l-wx------ 1 root root 64 Nov 26 08:50 2 -> pipe:[28844] 11/26 08:50:08 DEBUG| utils:0153| [stdout] # l-wx------ 1 root root 64 Nov 26 08:50 3 -> pipe:[27803] 11/26 08:50:08 DEBUG| utils:0153| [stdout] # l-wx------ 1 root root 64 Nov 26 08:50 4 -> pipe:[26387] 11/26 08:50:08 DEBUG| utils:0153| [stdout] # l-wx------ 1 root root 64 Nov 26 08:50 5 -> /home/ubuntu/autotest/client/results/default/debug/client.WARNING 11/26 08:50:08 DEBUG| utils:0153| [stdout] # l-wx------ 1 root root 64 Nov 26 08:50 6 -> /home/ubuntu/autotest/client/results/default/debug/client.ERROR 11/26 08:50:08 DEBUG| utils:0153| [stdout] # lrwx------ 1 root root 64 Nov 26 08:50 7 -> /dev/pts/0 11/26 08:50:08 DEBUG| utils:0153| [stdout] # lrwx------ 1 root root 64 Nov 26 08:50 8 -> /memfd:test (deleted) 11/26 08:50:08 DEBUG| utils:0153| [stdout] # lrwx------ 1 root root 64 Nov 26 08:50 9 -> /dev/pts/0 11/26 08:50:08 DEBUG| utils:0153| [stdout] # # seccomp_bpf.c:3993:user_notification_addfd:Expected listener (18) == nextfd++ (9) 11/26 08:50:09 DEBUG| utils:0153| [stdout] # # user_notification_addfd: Test terminated by assertion 11/26 08:50:09 DEBUG| utils:0153| [stdout] # # FAIL global.user_notification_addfd As we can see memfd has been allocated in a hole (fd=8) and listener will get fd=18, so checking for sequential fd numbers is not working in this case. > > # user_notification_addfd: Test terminated by assertion > > > > Simply check if memfd and listener are valid file descriptors and start > > counting for progressive file checking with the listener fd. > > Hm, so I attempted to fix this once already: > 93e720d710df ("selftests/seccomp: More closely track fds being assigned") > so I'm not sure the proposed patch really improves it in the general > case. I agree that my patch doesn't fix 100% of the cases, we may still have fd holes. > > > Fixes: 93e720d710df ("selftests/seccomp: More closely track fds being assigned") > > Signed-off-by: Andrea Righi <andrea.righi@canonical.com> > > --- > > tools/testing/selftests/seccomp/seccomp_bpf.c | 5 ++--- > > 1 file changed, 2 insertions(+), 3 deletions(-) > > > > diff --git a/tools/testing/selftests/seccomp/seccomp_bpf.c b/tools/testing/selftests/seccomp/seccomp_bpf.c > > index d425688cf59c..4f37153378a1 100644 > > --- a/tools/testing/selftests/seccomp/seccomp_bpf.c > > +++ b/tools/testing/selftests/seccomp/seccomp_bpf.c > > @@ -3975,18 +3975,17 @@ TEST(user_notification_addfd) > > /* There may be arbitrary already-open fds at test start. */ > > memfd = memfd_create("test", 0); > > ASSERT_GE(memfd, 0); > > - nextfd = memfd + 1; > > > > ret = prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0); > > ASSERT_EQ(0, ret) { > > TH_LOG("Kernel does not support PR_SET_NO_NEW_PRIVS!"); > > } > > > > - /* fd: 4 */ > > /* Check that the basic notification machinery works */ > > listener = user_notif_syscall(__NR_getppid, > > SECCOMP_FILTER_FLAG_NEW_LISTENER); > > - ASSERT_EQ(listener, nextfd++); > > + ASSERT_GE(listener, 0); > > + nextfd = listener + 1; > > e.g. if there was a hole in the fd map for memfd, why not listener too? > > Should the test dup2 memfd up to fd 100 and start counting there or > something? What is the condition that fills the fds for this process? How about getting the allocated fd numbers from /proc/pid/fd and figuring out the next fd number taking also the holes into account? Thanks, -Andrea
diff --git a/tools/testing/selftests/seccomp/seccomp_bpf.c b/tools/testing/selftests/seccomp/seccomp_bpf.c index d425688cf59c..4f37153378a1 100644 --- a/tools/testing/selftests/seccomp/seccomp_bpf.c +++ b/tools/testing/selftests/seccomp/seccomp_bpf.c @@ -3975,18 +3975,17 @@ TEST(user_notification_addfd) /* There may be arbitrary already-open fds at test start. */ memfd = memfd_create("test", 0); ASSERT_GE(memfd, 0); - nextfd = memfd + 1; ret = prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0); ASSERT_EQ(0, ret) { TH_LOG("Kernel does not support PR_SET_NO_NEW_PRIVS!"); } - /* fd: 4 */ /* Check that the basic notification machinery works */ listener = user_notif_syscall(__NR_getppid, SECCOMP_FILTER_FLAG_NEW_LISTENER); - ASSERT_EQ(listener, nextfd++); + ASSERT_GE(listener, 0); + nextfd = listener + 1; pid = fork(); ASSERT_GE(pid, 0);
There might be an arbitrary free open fd slot when we run the addfd sub-test, so checking for progressive numbers of file descriptors starting from memfd is not always a reliable check and we could get the following failure: # RUN global.user_notification_addfd ... # seccomp_bpf.c:3989:user_notification_addfd:Expected listener (18) == nextfd++ (9) # user_notification_addfd: Test terminated by assertion Simply check if memfd and listener are valid file descriptors and start counting for progressive file checking with the listener fd. Fixes: 93e720d710df ("selftests/seccomp: More closely track fds being assigned") Signed-off-by: Andrea Righi <andrea.righi@canonical.com> --- tools/testing/selftests/seccomp/seccomp_bpf.c | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-)