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Date: Mon, 29 Aug 2022 10:49:45 -0700
From: Kuniyuki Iwashima <kuniyu@...zon.com>
To: <kuniyu@...zon.com>
CC: <ayudutta@...zon.com>, <brauner@...nel.org>,
<keescook@...omium.org>, <kuni1840@...il.com>,
<linux-kernel@...r.kernel.org>, <luto@...capital.net>,
<syzbot+ab17848fe269b573eb71@...kaller.appspotmail.com>,
<wad@...omium.org>
Subject: [PATCH v3] seccomp: Move copy_seccomp() to no failure path.
Hi Kees,
Could you take a look at this?
Thank you.
From: Kuniyuki Iwashima <kuniyu@...zon.com>
Date: Tue, 23 Aug 2022 08:45:32 -0700
> 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 commit 3a15fb6ed92c ("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: 3a15fb6ed92c ("seccomp: release filter after task is fully dead")
> Reported-by: syzbot+ab17848fe269b573eb71@...kaller.appspotmail.com
> Reported-by: Ayushman Dutta <ayudutta@...zon.com>
> Suggested-by: Kees Cook <keescook@...omium.org>
> Signed-off-by: Kuniyuki Iwashima <kuniyu@...zon.com>
> Reviewed-by: Christian Brauner (Microsoft) <brauner@...nel.org>
> ---
> v3:
> * Fix build failure for CONFIG_SECCOMP=n case
>
> v2: https://lore.kernel.org/lkml/20220823004806.38681-1-kuniyu@amazon.com/
> * Move copy_seccomp() after no failure path instead of adding
> seccomp_filter_release() in the failure path.
>
> v1: https://lore.kernel.org/lkml/20220822204436.26631-1-kuniyu@amazon.com/
> ---
> kernel/fork.c | 17 +++++++++++------
> 1 file changed, 11 insertions(+), 6 deletions(-)
>
> diff --git a/kernel/fork.c b/kernel/fork.c
> index 90c85b17bf69..6ac1cc62f197 100644
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -537,6 +537,9 @@ void put_task_stack(struct task_struct *tsk)
>
> void free_task(struct task_struct *tsk)
> {
> +#ifdef CONFIG_SECCOMP
> + WARN_ON_ONCE(tsk->seccomp.filter);
> +#endif
> release_user_cpus_ptr(tsk);
> scs_release(tsk);
>
> @@ -2409,12 +2412,6 @@ static __latent_entropy struct task_struct *copy_process(
>
> spin_lock(¤t->sighand->siglock);
>
> - /*
> - * Copy seccomp details explicitly here, in case they were changed
> - * before holding sighand lock.
> - */
> - copy_seccomp(p);
> -
> rv_task_fork(p);
>
> rseq_fork(p, clone_flags);
> @@ -2431,6 +2428,14 @@ static __latent_entropy struct task_struct *copy_process(
> goto bad_fork_cancel_cgroup;
> }
>
> + /* No more failure paths after this point. */
> +
> + /*
> + * Copy seccomp details explicitly here, in case they were changed
> + * before holding sighand lock.
> + */
> + copy_seccomp(p);
> +
> init_task_pid_links(p);
> if (likely(p->pid)) {
> ptrace_init_task(p, (clone_flags & CLONE_PTRACE) || trace);
> --
> 2.30.2
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