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![Eric W. Biederman](/assets/img/avatar_default.png)
As Andy pointed out that there are races between
force_sig_info_to_task and sigaction[1] when force_sig_info_task. As
Kees discovered[2] ptrace is also able to change these signals.
In the case of seeccomp killing a process with a signal it is a
security violation to allow the signal to be caught or manipulated.
Solve this problem by introducing a new flag SA_IMMUTABLE that
prevents sigaction and ptrace from modifying these forced signals.
This flag is carefully made kernel internal so that no new ABI is
introduced.
Longer term I think this can be solved by guaranteeing short circuit
delivery of signals in this case. Unfortunately reliable and
guaranteed short circuit delivery of these signals is still a ways off
from being implemented, tested, and merged. So I have implemented a much
simpler alternative for now.
[1] https://lkml.kernel.org/r/b5d52d25-7bde-4030-a7b1-7c6f8ab90660@www.fastmail.com
[2] https://lkml.kernel.org/r/202110281136.5CE65399A7@keescook
Cc: stable@vger.kernel.org
Fixes: 307d522f5e
("signal/seccomp: Refactor seccomp signal and coredump generation")
Tested-by: Andrea Righi <andrea.righi@canonical.com>
Tested-by: Kees Cook <keescook@chromium.org>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
88 lines
1.7 KiB
C
88 lines
1.7 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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#ifndef _LINUX_SIGNAL_TYPES_H
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#define _LINUX_SIGNAL_TYPES_H
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/*
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* Basic signal handling related data type definitions:
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*/
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#include <linux/list.h>
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#include <uapi/linux/signal.h>
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typedef struct kernel_siginfo {
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__SIGINFO;
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} kernel_siginfo_t;
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struct ucounts;
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/*
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* Real Time signals may be queued.
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*/
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struct sigqueue {
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struct list_head list;
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int flags;
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kernel_siginfo_t info;
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struct ucounts *ucounts;
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};
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/* flags values. */
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#define SIGQUEUE_PREALLOC 1
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struct sigpending {
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struct list_head list;
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sigset_t signal;
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};
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struct sigaction {
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#ifndef __ARCH_HAS_IRIX_SIGACTION
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__sighandler_t sa_handler;
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unsigned long sa_flags;
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#else
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unsigned int sa_flags;
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__sighandler_t sa_handler;
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#endif
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#ifdef __ARCH_HAS_SA_RESTORER
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__sigrestore_t sa_restorer;
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#endif
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sigset_t sa_mask; /* mask last for extensibility */
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};
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struct k_sigaction {
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struct sigaction sa;
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#ifdef __ARCH_HAS_KA_RESTORER
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__sigrestore_t ka_restorer;
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#endif
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};
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#ifdef CONFIG_OLD_SIGACTION
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struct old_sigaction {
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__sighandler_t sa_handler;
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old_sigset_t sa_mask;
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unsigned long sa_flags;
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__sigrestore_t sa_restorer;
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};
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#endif
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struct ksignal {
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struct k_sigaction ka;
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kernel_siginfo_t info;
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int sig;
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};
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/* Used to kill the race between sigaction and forced signals */
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#define SA_IMMUTABLE 0x00800000
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#ifndef __ARCH_UAPI_SA_FLAGS
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#ifdef SA_RESTORER
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#define __ARCH_UAPI_SA_FLAGS SA_RESTORER
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#else
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#define __ARCH_UAPI_SA_FLAGS 0
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#endif
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#endif
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#define UAPI_SA_FLAGS \
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(SA_NOCLDSTOP | SA_NOCLDWAIT | SA_SIGINFO | SA_ONSTACK | SA_RESTART | \
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SA_NODEFER | SA_RESETHAND | SA_EXPOSE_TAGBITS | __ARCH_UAPI_SA_FLAGS)
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#endif /* _LINUX_SIGNAL_TYPES_H */
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