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51891498f2
The restriction introduced in 7a0df7fbc1 ("seccomp: Make NEW_LISTENER and
TSYNC flags exclusive") is mostly artificial: there is enough information
in a seccomp user notification to tell which thread triggered a
notification. The reason it was introduced is because TSYNC makes the
syscall return a thread-id on failure, and NEW_LISTENER returns an fd, and
there's no way to distinguish between these two cases (well, I suppose the
caller could check all fds it has, then do the syscall, and if the return
value was an fd that already existed, then it must be a thread id, but
bleh).
Matthew would like to use these two flags together in the Chrome sandbox
which wants to use TSYNC for video drivers and NEW_LISTENER to proxy
syscalls.
So, let's fix this ugliness by adding another flag, TSYNC_ESRCH, which
tells the kernel to just return -ESRCH on a TSYNC error. This way,
NEW_LISTENER (and any subsequent seccomp() commands that want to return
positive values) don't conflict with each other.
Suggested-by: Matthew Denton <mpdenton@google.com>
Signed-off-by: Tycho Andersen <tycho@tycho.ws>
Link: https://lore.kernel.org/r/20200304180517.23867-1-tycho@tycho.ws
Signed-off-by: Kees Cook <keescook@chromium.org>
128 lines
4.9 KiB
C
128 lines
4.9 KiB
C
/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
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#ifndef _UAPI_LINUX_SECCOMP_H
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#define _UAPI_LINUX_SECCOMP_H
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#include <linux/compiler.h>
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#include <linux/types.h>
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/* Valid values for seccomp.mode and prctl(PR_SET_SECCOMP, <mode>) */
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#define SECCOMP_MODE_DISABLED 0 /* seccomp is not in use. */
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#define SECCOMP_MODE_STRICT 1 /* uses hard-coded filter. */
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#define SECCOMP_MODE_FILTER 2 /* uses user-supplied filter. */
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/* Valid operations for seccomp syscall. */
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#define SECCOMP_SET_MODE_STRICT 0
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#define SECCOMP_SET_MODE_FILTER 1
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#define SECCOMP_GET_ACTION_AVAIL 2
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#define SECCOMP_GET_NOTIF_SIZES 3
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/* Valid flags for SECCOMP_SET_MODE_FILTER */
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#define SECCOMP_FILTER_FLAG_TSYNC (1UL << 0)
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#define SECCOMP_FILTER_FLAG_LOG (1UL << 1)
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#define SECCOMP_FILTER_FLAG_SPEC_ALLOW (1UL << 2)
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#define SECCOMP_FILTER_FLAG_NEW_LISTENER (1UL << 3)
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#define SECCOMP_FILTER_FLAG_TSYNC_ESRCH (1UL << 4)
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/*
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* All BPF programs must return a 32-bit value.
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* The bottom 16-bits are for optional return data.
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* The upper 16-bits are ordered from least permissive values to most,
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* as a signed value (so 0x8000000 is negative).
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*
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* The ordering ensures that a min_t() over composed return values always
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* selects the least permissive choice.
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*/
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#define SECCOMP_RET_KILL_PROCESS 0x80000000U /* kill the process */
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#define SECCOMP_RET_KILL_THREAD 0x00000000U /* kill the thread */
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#define SECCOMP_RET_KILL SECCOMP_RET_KILL_THREAD
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#define SECCOMP_RET_TRAP 0x00030000U /* disallow and force a SIGSYS */
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#define SECCOMP_RET_ERRNO 0x00050000U /* returns an errno */
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#define SECCOMP_RET_USER_NOTIF 0x7fc00000U /* notifies userspace */
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#define SECCOMP_RET_TRACE 0x7ff00000U /* pass to a tracer or disallow */
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#define SECCOMP_RET_LOG 0x7ffc0000U /* allow after logging */
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#define SECCOMP_RET_ALLOW 0x7fff0000U /* allow */
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/* Masks for the return value sections. */
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#define SECCOMP_RET_ACTION_FULL 0xffff0000U
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#define SECCOMP_RET_ACTION 0x7fff0000U
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#define SECCOMP_RET_DATA 0x0000ffffU
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/**
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* struct seccomp_data - the format the BPF program executes over.
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* @nr: the system call number
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* @arch: indicates system call convention as an AUDIT_ARCH_* value
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* as defined in <linux/audit.h>.
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* @instruction_pointer: at the time of the system call.
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* @args: up to 6 system call arguments always stored as 64-bit values
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* regardless of the architecture.
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*/
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struct seccomp_data {
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int nr;
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__u32 arch;
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__u64 instruction_pointer;
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__u64 args[6];
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};
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struct seccomp_notif_sizes {
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__u16 seccomp_notif;
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__u16 seccomp_notif_resp;
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__u16 seccomp_data;
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};
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struct seccomp_notif {
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__u64 id;
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__u32 pid;
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__u32 flags;
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struct seccomp_data data;
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};
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/*
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* Valid flags for struct seccomp_notif_resp
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*
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* Note, the SECCOMP_USER_NOTIF_FLAG_CONTINUE flag must be used with caution!
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* If set by the process supervising the syscalls of another process the
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* syscall will continue. This is problematic because of an inherent TOCTOU.
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* An attacker can exploit the time while the supervised process is waiting on
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* a response from the supervising process to rewrite syscall arguments which
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* are passed as pointers of the intercepted syscall.
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* It should be absolutely clear that this means that the seccomp notifier
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* _cannot_ be used to implement a security policy! It should only ever be used
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* in scenarios where a more privileged process supervises the syscalls of a
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* lesser privileged process to get around kernel-enforced security
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* restrictions when the privileged process deems this safe. In other words,
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* in order to continue a syscall the supervising process should be sure that
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* another security mechanism or the kernel itself will sufficiently block
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* syscalls if arguments are rewritten to something unsafe.
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*
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* Similar precautions should be applied when stacking SECCOMP_RET_USER_NOTIF
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* or SECCOMP_RET_TRACE. For SECCOMP_RET_USER_NOTIF filters acting on the
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* same syscall, the most recently added filter takes precedence. This means
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* that the new SECCOMP_RET_USER_NOTIF filter can override any
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* SECCOMP_IOCTL_NOTIF_SEND from earlier filters, essentially allowing all
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* such filtered syscalls to be executed by sending the response
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* SECCOMP_USER_NOTIF_FLAG_CONTINUE. Note that SECCOMP_RET_TRACE can equally
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* be overriden by SECCOMP_USER_NOTIF_FLAG_CONTINUE.
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*/
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#define SECCOMP_USER_NOTIF_FLAG_CONTINUE (1UL << 0)
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struct seccomp_notif_resp {
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__u64 id;
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__s64 val;
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__s32 error;
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__u32 flags;
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};
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#define SECCOMP_IOC_MAGIC '!'
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#define SECCOMP_IO(nr) _IO(SECCOMP_IOC_MAGIC, nr)
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#define SECCOMP_IOR(nr, type) _IOR(SECCOMP_IOC_MAGIC, nr, type)
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#define SECCOMP_IOW(nr, type) _IOW(SECCOMP_IOC_MAGIC, nr, type)
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#define SECCOMP_IOWR(nr, type) _IOWR(SECCOMP_IOC_MAGIC, nr, type)
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/* Flags for seccomp notification fd ioctl. */
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#define SECCOMP_IOCTL_NOTIF_RECV SECCOMP_IOWR(0, struct seccomp_notif)
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#define SECCOMP_IOCTL_NOTIF_SEND SECCOMP_IOWR(1, \
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struct seccomp_notif_resp)
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#define SECCOMP_IOCTL_NOTIF_ID_VALID SECCOMP_IOR(2, __u64)
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#endif /* _UAPI_LINUX_SECCOMP_H */
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