seccomp: Move copy_seccomp() to no failure path.
Bugzilla: https://bugzilla.redhat.com/2218682 commit a1140cb215fa13dcec06d12ba0c3ee105633b7c4 Author: Kuniyuki Iwashima <kuniyu@amazon.com> Date: Tue Aug 23 08:45:32 2022 -0700 seccomp: Move copy_seccomp() to no failure path. Our syzbot instance reported memory leaks in do_seccomp() [0], similar to the report [1]. It shows that we miss freeing struct seccomp_filter and some objects included in it. We can reproduce the issue with the program below [2] which calls one seccomp() and two clone() syscalls. The first clone()d child exits earlier than its parent and sends a signal to kill it during the second clone(), more precisely before the fatal_signal_pending() test in copy_process(). When the parent receives the signal, it has to destroy the embryonic process and return -EINTR to user space. In the failure path, we have to call seccomp_filter_release() to decrement the filter's refcount. Initially, we called it in free_task() called from the failure path, but the commit3a15fb6ed9("seccomp: release filter after task is fully dead") moved it to release_task() to notify user space as early as possible that the filter is no longer used. To keep the change and current seccomp refcount semantics, let's move copy_seccomp() just after the signal check and add a WARN_ON_ONCE() in free_task() for future debugging. [0]: unreferenced object 0xffff8880063add00 (size 256): comm "repro_seccomp", pid 230, jiffies 4294687090 (age 9.914s) hex dump (first 32 bytes): 01 00 00 00 01 00 00 00 00 00 00 00 00 00 00 00 ................ ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ................ backtrace: do_seccomp (./include/linux/slab.h:600 ./include/linux/slab.h:733 kernel/seccomp.c:666 kernel/seccomp.c:708 kernel/seccomp.c:1871 kernel/seccomp.c:1991) do_syscall_64 (arch/x86/entry/common.c:50 arch/x86/entry/common.c:80) entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:120) unreferenced object 0xffffc90000035000 (size 4096): comm "repro_seccomp", pid 230, jiffies 4294687090 (age 9.915s) hex dump (first 32 bytes): 01 00 00 00 00 00 00 00 00 00 00 00 05 00 00 00 ................ 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ backtrace: __vmalloc_node_range (mm/vmalloc.c:3226) __vmalloc_node (mm/vmalloc.c:3261 (discriminator 4)) bpf_prog_alloc_no_stats (kernel/bpf/core.c:91) bpf_prog_alloc (kernel/bpf/core.c:129) bpf_prog_create_from_user (net/core/filter.c:1414) do_seccomp (kernel/seccomp.c:671 kernel/seccomp.c:708 kernel/seccomp.c:1871 kernel/seccomp.c:1991) do_syscall_64 (arch/x86/entry/common.c:50 arch/x86/entry/common.c:80) entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:120) unreferenced object 0xffff888003fa1000 (size 1024): comm "repro_seccomp", pid 230, jiffies 4294687090 (age 9.915s) hex dump (first 32 bytes): 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ backtrace: bpf_prog_alloc_no_stats (./include/linux/slab.h:600 ./include/linux/slab.h:733 kernel/bpf/core.c:95) bpf_prog_alloc (kernel/bpf/core.c:129) bpf_prog_create_from_user (net/core/filter.c:1414) do_seccomp (kernel/seccomp.c:671 kernel/seccomp.c:708 kernel/seccomp.c:1871 kernel/seccomp.c:1991) do_syscall_64 (arch/x86/entry/common.c:50 arch/x86/entry/common.c:80) entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:120) unreferenced object 0xffff888006360240 (size 16): comm "repro_seccomp", pid 230, jiffies 4294687090 (age 9.915s) hex dump (first 16 bytes): 01 00 37 00 76 65 72 6c e0 83 01 06 80 88 ff ff ..7.verl........ backtrace: bpf_prog_store_orig_filter (net/core/filter.c:1137) bpf_prog_create_from_user (net/core/filter.c:1428) do_seccomp (kernel/seccomp.c:671 kernel/seccomp.c:708 kernel/seccomp.c:1871 kernel/seccomp.c:1991) do_syscall_64 (arch/x86/entry/common.c:50 arch/x86/entry/common.c:80) entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:120) unreferenced object 0xffff8880060183e0 (size 8): comm "repro_seccomp", pid 230, jiffies 4294687090 (age 9.915s) hex dump (first 8 bytes): 06 00 00 00 00 00 ff 7f ........ backtrace: kmemdup (mm/util.c:129) bpf_prog_store_orig_filter (net/core/filter.c:1144) bpf_prog_create_from_user (net/core/filter.c:1428) do_seccomp (kernel/seccomp.c:671 kernel/seccomp.c:708 kernel/seccomp.c:1871 kernel/seccomp.c:1991) do_syscall_64 (arch/x86/entry/common.c:50 arch/x86/entry/common.c:80) entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:120) [1]: https://syzkaller.appspot.com/bug?id=2809bb0ac77ad9aa3f4afe42d6a610aba594a987 [2]: #define _GNU_SOURCE #include <sched.h> #include <signal.h> #include <unistd.h> #include <sys/syscall.h> #include <linux/filter.h> #include <linux/seccomp.h> void main(void) { struct sock_filter filter[] = { BPF_STMT(BPF_RET | BPF_K, SECCOMP_RET_ALLOW), }; struct sock_fprog fprog = { .len = sizeof(filter) / sizeof(filter[0]), .filter = filter, }; long i, pid; syscall(__NR_seccomp, SECCOMP_SET_MODE_FILTER, 0, &fprog); for (i = 0; i < 2; i++) { pid = syscall(__NR_clone, CLONE_NEWNET | SIGKILL, NULL, NULL, 0); if (pid == 0) return; } } Fixes:3a15fb6ed9("seccomp: release filter after task is fully dead") Reported-by: syzbot+ab17848fe269b573eb71@syzkaller.appspotmail.com Reported-by: Ayushman Dutta <ayudutta@amazon.com> Suggested-by: Kees Cook <keescook@chromium.org> Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com> Reviewed-by: Christian Brauner (Microsoft) <brauner@kernel.org> Signed-off-by: Kees Cook <keescook@chromium.org> Link: https://lore.kernel.org/r/20220823154532.82913-1-kuniyu@amazon.com Signed-off-by: Viktor Malik <vmalik@redhat.com>
This commit is contained in:
Viktor Malik
parent
35970745f2
commit
eedd4d3960
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@ -537,6 +537,9 @@ void put_task_stack(struct task_struct *tsk)
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void free_task(struct task_struct *tsk)
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{
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#ifdef CONFIG_SECCOMP
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WARN_ON_ONCE(tsk->seccomp.filter);
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#endif
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release_user_cpus_ptr(tsk);
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scs_release(tsk);
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@ -2390,12 +2393,6 @@ static __latent_entropy struct task_struct *copy_process(
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spin_lock(¤t->sighand->siglock);
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/*
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* Copy seccomp details explicitly here, in case they were changed
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* before holding sighand lock.
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*/
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copy_seccomp(p);
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rv_task_fork(p);
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rseq_fork(p, clone_flags);
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@ -2412,6 +2409,14 @@ static __latent_entropy struct task_struct *copy_process(
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goto bad_fork_cancel_cgroup;
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}
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/* No more failure paths after this point. */
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/*
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* Copy seccomp details explicitly here, in case they were changed
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* before holding sighand lock.
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*/
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copy_seccomp(p);
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init_task_pid_links(p);
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if (likely(p->pid)) {
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ptrace_init_task(p, (clone_flags & CLONE_PTRACE) || trace);
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