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seccomp: Add SECCOMP_RET_TRAP

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Adds a new return value to seccomp filters that triggers a SIGSYS to be
delivered with the new SYS_SECCOMP si_code.

This allows in-process system call emulation, including just specifying
an errno or cleanly dumping core, rather than just dying.

Suggested-by: Markus Gutschke <markus@chromium.org>
Suggested-by: Julien Tinnes <jln@chromium.org>
Signed-off-by: Will Drewry <wad@chromium.org>
Acked-by: Eric Paris <eparis@redhat.com>

v18: - acked-by, rebase
     - don't mention secure_computing_int() anymore
v15: - use audit_seccomp/skip
     - pad out error spacing; clean up switch (indan@nul.nu)
v14: - n/a
v13: - rebase on to 88ebdda615
v12: - rebase on to linux-next
v11: - clarify the comment (indan@nul.nu)
     - s/sigtrap/sigsys
v10: - use SIGSYS, syscall_get_arch, updates arch/Kconfig
       note suggested-by (though original suggestion had other behaviors)
v9:  - changes to SIGILL
v8:  - clean up based on changes to dependent patches
v7:  - introduction
Signed-off-by: James Morris <james.l.morris@oracle.com>
This commit is contained in:
Will Drewry 2012-04-12 16:48:01 -05:00 committed by James Morris
parent a0727e8ce5
commit bb6ea4301a
4 changed files with 37 additions and 6 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

14
arch/Kconfig
View File

@ -219,11 +219,15 @@ config ARCH_WANT_OLD_COMPAT_IPC
config HAVE_ARCH_SECCOMP_FILTER
bool
help
This symbol should be selected by an architecure if it provides
asm/syscall.h, specifically syscall_get_arguments(),
syscall_get_arch(), and syscall_set_return_value(). Additionally,
its system call entry path must respect a return value of -1 from
__secure_computing() and/or secure_computing().
This symbol should be selected by an architecure if it provides:
asm/syscall.h:
- syscall_get_arch()
- syscall_get_arguments()
- syscall_rollback()
- syscall_set_return_value()
SIGSYS siginfo_t support must be implemented.
__secure_computing()/secure_computing()'s return value must be
checked, with -1 resulting in the syscall being skipped.
config SECCOMP_FILTER
def_bool y

2
include/asm-generic/siginfo.h
View File

@ -93,7 +93,7 @@ typedef struct siginfo {
/* SIGSYS */
struct {
void __user *_call_addr; /* calling insn */
void __user *_call_addr; /* calling user insn */
int _syscall; /* triggering system call number */
unsigned int _arch; /* AUDIT_ARCH_* of syscall */
} _sigsys;

1
include/linux/seccomp.h
View File

@ -19,6 +19,7 @@
* selects the least permissive choice.
*/
#define SECCOMP_RET_KILL 0x00000000U /* kill the task immediately */
#define SECCOMP_RET_TRAP 0x00030000U /* disallow and force a SIGSYS */
#define SECCOMP_RET_ERRNO 0x00050000U /* returns an errno */
#define SECCOMP_RET_ALLOW 0x7fff0000U /* allow */

26
kernel/seccomp.c
View File

@ -332,6 +332,26 @@ void put_seccomp_filter(struct task_struct *tsk)
kfree(freeme);
}
}
/**
* seccomp_send_sigsys - signals the task to allow in-process syscall emulation
* @syscall: syscall number to send to userland
* @reason: filter-supplied reason code to send to userland (via si_errno)
*
* Forces a SIGSYS with a code of SYS_SECCOMP and related sigsys info.
*/
static void seccomp_send_sigsys(int syscall, int reason)
{
struct siginfo info;
memset(&info, 0, sizeof(info));
info.si_signo = SIGSYS;
info.si_code = SYS_SECCOMP;
info.si_call_addr = (void __user *)KSTK_EIP(current);
info.si_errno = reason;
info.si_arch = syscall_get_arch(current, task_pt_regs(current));
info.si_syscall = syscall;
force_sig_info(SIGSYS, &info, current);
}
#endif /* CONFIG_SECCOMP_FILTER */
/*
@ -382,6 +402,12 @@ int __secure_computing(int this_syscall)
syscall_set_return_value(current, task_pt_regs(current),
-data, 0);
goto skip;
case SECCOMP_RET_TRAP:
/* Show the handler the original registers. */
syscall_rollback(current, task_pt_regs(current));
/* Let the filter pass back 16 bits of data. */
seccomp_send_sigsys(this_syscall, data);
goto skip;
case SECCOMP_RET_ALLOW:
return 0;
case SECCOMP_RET_KILL: