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From: Hao Sun <sunhao.th@gmail.com>
To: bpf@vger.kernel.org
Cc: ast@kernel.org, daniel@iogearbox.net, john.fastabend@gmail.com,
andrii@kernel.org, martin.lau@linux.dev, song@kernel.org,
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linux-kernel@vger.kernel.org, Hao Sun <sunhao.th@gmail.com>
Subject: [PATCH] bpf: skip task with pid=1 in send_signal_common()
Date: Fri, 6 Jan 2023 16:48:38 +0800
Message-Id: <20230106084838.12690-1-sunhao.th@gmail.com>
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bpf: skip task with pid=1 in send_signal_common()
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Commit Message
Hao Sun
Jan. 6, 2023, 8:48 a.m. UTC
The following kernel panic can be triggered when a task with pid=1
attach a prog that attempts to send killing signal to itself, also
see [1] for more details:
Kernel panic - not syncing: Attempted to kill init! exitcode=0x0000000b
CPU: 3 PID: 1 Comm: systemd Not tainted 6.1.0-09652-g59fe41b5255f #148
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:88 [inline]
dump_stack_lvl+0x100/0x178 lib/dump_stack.c:106
panic+0x2c4/0x60f kernel/panic.c:275
do_exit.cold+0x63/0xe4 kernel/exit.c:789
do_group_exit+0xd4/0x2a0 kernel/exit.c:950
get_signal+0x2460/0x2600 kernel/signal.c:2858
arch_do_signal_or_restart+0x78/0x5d0 arch/x86/kernel/signal.c:306
exit_to_user_mode_loop kernel/entry/common.c:168 [inline]
exit_to_user_mode_prepare+0x15f/0x250 kernel/entry/common.c:203
__syscall_exit_to_user_mode_work kernel/entry/common.c:285 [inline]
syscall_exit_to_user_mode+0x1d/0x50 kernel/entry/common.c:296
do_syscall_64+0x44/0xb0 arch/x86/entry/common.c:86
entry_SYSCALL_64_after_hwframe+0x63/0xcd
So skip task with pid=1 in bpf_send_signal_common() to avoid the panic.
[1] https://lore.kernel.org/bpf/20221222043507.33037-1-sunhao.th@gmail.com
Signed-off-by: Hao Sun <sunhao.th@gmail.com>
---
kernel/trace/bpf_trace.c | 3 +++
1 file changed, 3 insertions(+)
base-commit: 4aea86b4033f92f01547e6d4388d4451ae9b0980
Comments
On Fri, Jan 6, 2023 at 12:48 AM Hao Sun <sunhao.th@gmail.com> wrote: > > The following kernel panic can be triggered when a task with pid=1 > attach a prog that attempts to send killing signal to itself, also > see [1] for more details: > > Kernel panic - not syncing: Attempted to kill init! exitcode=0x0000000b > CPU: 3 PID: 1 Comm: systemd Not tainted 6.1.0-09652-g59fe41b5255f #148 > Call Trace: > <TASK> > __dump_stack lib/dump_stack.c:88 [inline] > dump_stack_lvl+0x100/0x178 lib/dump_stack.c:106 > panic+0x2c4/0x60f kernel/panic.c:275 > do_exit.cold+0x63/0xe4 kernel/exit.c:789 > do_group_exit+0xd4/0x2a0 kernel/exit.c:950 > get_signal+0x2460/0x2600 kernel/signal.c:2858 > arch_do_signal_or_restart+0x78/0x5d0 arch/x86/kernel/signal.c:306 > exit_to_user_mode_loop kernel/entry/common.c:168 [inline] > exit_to_user_mode_prepare+0x15f/0x250 kernel/entry/common.c:203 > __syscall_exit_to_user_mode_work kernel/entry/common.c:285 [inline] > syscall_exit_to_user_mode+0x1d/0x50 kernel/entry/common.c:296 > do_syscall_64+0x44/0xb0 arch/x86/entry/common.c:86 > entry_SYSCALL_64_after_hwframe+0x63/0xcd > > So skip task with pid=1 in bpf_send_signal_common() to avoid the panic. > > [1] https://lore.kernel.org/bpf/20221222043507.33037-1-sunhao.th@gmail.com > > Signed-off-by: Hao Sun <sunhao.th@gmail.com> Acked-by: Stanislav Fomichev <sdf@google.com> > --- > kernel/trace/bpf_trace.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c > index 23ce498bca97..ed21ab9fe846 100644 > --- a/kernel/trace/bpf_trace.c > +++ b/kernel/trace/bpf_trace.c > @@ -844,6 +844,9 @@ static int bpf_send_signal_common(u32 sig, enum pid_type type) > */ > if (unlikely(current->flags & (PF_KTHREAD | PF_EXITING))) > return -EPERM; > + /* Task should not be pid=1 to avoid kernel panic. */ > + if (unlikely(is_global_init(current))) > + return -EPERM; > if (unlikely(!nmi_uaccess_okay())) > return -EPERM; > > > base-commit: 4aea86b4033f92f01547e6d4388d4451ae9b0980 > -- > 2.39.0 >
On 1/6/23 8:44 PM, Stanislav Fomichev wrote: > On Fri, Jan 6, 2023 at 12:48 AM Hao Sun <sunhao.th@gmail.com> wrote: >> >> The following kernel panic can be triggered when a task with pid=1 >> attach a prog that attempts to send killing signal to itself, also >> see [1] for more details: >> >> Kernel panic - not syncing: Attempted to kill init! exitcode=0x0000000b >> CPU: 3 PID: 1 Comm: systemd Not tainted 6.1.0-09652-g59fe41b5255f #148 >> Call Trace: >> <TASK> >> __dump_stack lib/dump_stack.c:88 [inline] >> dump_stack_lvl+0x100/0x178 lib/dump_stack.c:106 >> panic+0x2c4/0x60f kernel/panic.c:275 >> do_exit.cold+0x63/0xe4 kernel/exit.c:789 >> do_group_exit+0xd4/0x2a0 kernel/exit.c:950 >> get_signal+0x2460/0x2600 kernel/signal.c:2858 >> arch_do_signal_or_restart+0x78/0x5d0 arch/x86/kernel/signal.c:306 >> exit_to_user_mode_loop kernel/entry/common.c:168 [inline] >> exit_to_user_mode_prepare+0x15f/0x250 kernel/entry/common.c:203 >> __syscall_exit_to_user_mode_work kernel/entry/common.c:285 [inline] >> syscall_exit_to_user_mode+0x1d/0x50 kernel/entry/common.c:296 >> do_syscall_64+0x44/0xb0 arch/x86/entry/common.c:86 >> entry_SYSCALL_64_after_hwframe+0x63/0xcd >> >> So skip task with pid=1 in bpf_send_signal_common() to avoid the panic. >> >> [1] https://lore.kernel.org/bpf/20221222043507.33037-1-sunhao.th@gmail.com >> >> Signed-off-by: Hao Sun <sunhao.th@gmail.com> > > Acked-by: Stanislav Fomichev <sdf@google.com> Looks good, agree & applied. These three tests could actually be refactored and also reused in bpf_probe_write_user() given also the latter should have no business to mess with pid 1. >> kernel/trace/bpf_trace.c | 3 +++ >> 1 file changed, 3 insertions(+) >> >> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c >> index 23ce498bca97..ed21ab9fe846 100644 >> --- a/kernel/trace/bpf_trace.c >> +++ b/kernel/trace/bpf_trace.c >> @@ -844,6 +844,9 @@ static int bpf_send_signal_common(u32 sig, enum pid_type type) >> */ >> if (unlikely(current->flags & (PF_KTHREAD | PF_EXITING))) >> return -EPERM; >> + /* Task should not be pid=1 to avoid kernel panic. */ >> + if (unlikely(is_global_init(current))) >> + return -EPERM; >> if (unlikely(!nmi_uaccess_okay())) >> return -EPERM; >> >> >> base-commit: 4aea86b4033f92f01547e6d4388d4451ae9b0980 >> -- >> 2.39.0 >>
Hello: This patch was applied to bpf/bpf.git (master) by Daniel Borkmann <daniel@iogearbox.net>: On Fri, 6 Jan 2023 16:48:38 +0800 you wrote: > The following kernel panic can be triggered when a task with pid=1 > attach a prog that attempts to send killing signal to itself, also > see [1] for more details: > > Kernel panic - not syncing: Attempted to kill init! exitcode=0x0000000b > CPU: 3 PID: 1 Comm: systemd Not tainted 6.1.0-09652-g59fe41b5255f #148 > Call Trace: > <TASK> > __dump_stack lib/dump_stack.c:88 [inline] > dump_stack_lvl+0x100/0x178 lib/dump_stack.c:106 > panic+0x2c4/0x60f kernel/panic.c:275 > do_exit.cold+0x63/0xe4 kernel/exit.c:789 > do_group_exit+0xd4/0x2a0 kernel/exit.c:950 > get_signal+0x2460/0x2600 kernel/signal.c:2858 > arch_do_signal_or_restart+0x78/0x5d0 arch/x86/kernel/signal.c:306 > exit_to_user_mode_loop kernel/entry/common.c:168 [inline] > exit_to_user_mode_prepare+0x15f/0x250 kernel/entry/common.c:203 > __syscall_exit_to_user_mode_work kernel/entry/common.c:285 [inline] > syscall_exit_to_user_mode+0x1d/0x50 kernel/entry/common.c:296 > do_syscall_64+0x44/0xb0 arch/x86/entry/common.c:86 > entry_SYSCALL_64_after_hwframe+0x63/0xcd > > [...] Here is the summary with links: - bpf: skip task with pid=1 in send_signal_common() https://git.kernel.org/bpf/bpf/c/a3d81bc1eaef You are awesome, thank you!
On Fri, Jan 06, 2023 at 02:18:38PM IST, Hao Sun wrote: > The following kernel panic can be triggered when a task with pid=1 > attach a prog that attempts to send killing signal to itself, also > see [1] for more details: > > Kernel panic - not syncing: Attempted to kill init! exitcode=0x0000000b > CPU: 3 PID: 1 Comm: systemd Not tainted 6.1.0-09652-g59fe41b5255f #148 > Call Trace: > <TASK> > __dump_stack lib/dump_stack.c:88 [inline] > dump_stack_lvl+0x100/0x178 lib/dump_stack.c:106 > panic+0x2c4/0x60f kernel/panic.c:275 > do_exit.cold+0x63/0xe4 kernel/exit.c:789 > do_group_exit+0xd4/0x2a0 kernel/exit.c:950 > get_signal+0x2460/0x2600 kernel/signal.c:2858 > arch_do_signal_or_restart+0x78/0x5d0 arch/x86/kernel/signal.c:306 > exit_to_user_mode_loop kernel/entry/common.c:168 [inline] > exit_to_user_mode_prepare+0x15f/0x250 kernel/entry/common.c:203 > __syscall_exit_to_user_mode_work kernel/entry/common.c:285 [inline] > syscall_exit_to_user_mode+0x1d/0x50 kernel/entry/common.c:296 > do_syscall_64+0x44/0xb0 arch/x86/entry/common.c:86 > entry_SYSCALL_64_after_hwframe+0x63/0xcd > > So skip task with pid=1 in bpf_send_signal_common() to avoid the panic. > > [1] https://lore.kernel.org/bpf/20221222043507.33037-1-sunhao.th@gmail.com > > Signed-off-by: Hao Sun <sunhao.th@gmail.com> > --- > kernel/trace/bpf_trace.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c > index 23ce498bca97..ed21ab9fe846 100644 > --- a/kernel/trace/bpf_trace.c > +++ b/kernel/trace/bpf_trace.c > @@ -844,6 +844,9 @@ static int bpf_send_signal_common(u32 sig, enum pid_type type) > */ > if (unlikely(current->flags & (PF_KTHREAD | PF_EXITING))) > return -EPERM; > + /* Task should not be pid=1 to avoid kernel panic. */ > + if (unlikely(is_global_init(current))) > + return -EPERM; Sorry for chiming in late. This seems a bit too restrictive, there are a lot of legitimate signals that can be sent to the init process (like the ones listed in man 1 systemd). Maybe you should only prevent sig == SIGKILL and not others?
diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c index 23ce498bca97..ed21ab9fe846 100644 --- a/kernel/trace/bpf_trace.c +++ b/kernel/trace/bpf_trace.c @@ -844,6 +844,9 @@ static int bpf_send_signal_common(u32 sig, enum pid_type type) */ if (unlikely(current->flags & (PF_KTHREAD | PF_EXITING))) return -EPERM; + /* Task should not be pid=1 to avoid kernel panic. */ + if (unlikely(is_global_init(current))) + return -EPERM; if (unlikely(!nmi_uaccess_okay())) return -EPERM;