bpf: Skip task with pid=1 in send_signal_common()

Overview

In the Linux kernel, the following vulnerability has been resolved:

bpf: Skip task with pid=1 in send_signal_common()

The following kernel panic can be triggered when a task with pid=1 attaches 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/[email protected]

Affected

• Linux >= 8b401f9ed2441ad9e219953927a842d24ed051fc < 4923160393b06a34759a11b17930d71e06f396f2
• Linux >= 8b401f9ed2441ad9e219953927a842d24ed051fc < a1c0263f1eb4deee132e11e52ee6982435460d81
• Linux >= 8b401f9ed2441ad9e219953927a842d24ed051fc < 0dfef503133565fa0bcf3268d8eeb5b181191a65
• Linux >= 8b401f9ed2441ad9e219953927a842d24ed051fc < 1283a01b6e19d05f7ed49584ea653947245cd41e
• Linux >= 8b401f9ed2441ad9e219953927a842d24ed051fc < a3d81bc1eaef48e34dd0b9b48eefed9e02a06451
• Linux 5.3

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.