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apparmor: add the ability to mediate signals

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Add signal mediation where the signal can be mediated based on the
signal, direction, or the label or the peer/target. The signal perms
are verified on a cross check to ensure policy consistency in the case
of incremental policy load/replacement.

The optimization of skipping the cross check when policy is guaranteed
to be consistent (single compile unit) remains to be done.

policy rules have the form of
  SIGNAL_RULE = [ QUALIFIERS ] 'signal' [ SIGNAL ACCESS PERMISSIONS ]
                [ SIGNAL SET ] [ SIGNAL PEER ]

  SIGNAL ACCESS PERMISSIONS = SIGNAL ACCESS | SIGNAL ACCESS LIST

  SIGNAL ACCESS LIST = '(' Comma or space separated list of SIGNAL
                           ACCESS ')'

  SIGNAL ACCESS = ( 'r' | 'w' | 'rw' | 'read' | 'write' | 'send' |
                    'receive' )

  SIGNAL SET = 'set' '=' '(' SIGNAL LIST ')'

  SIGNAL LIST = Comma or space separated list of SIGNALS

  SIGNALS = ( 'hup' | 'int' | 'quit' | 'ill' | 'trap' | 'abrt' |
              'bus' | 'fpe' | 'kill' | 'usr1' | 'segv' | 'usr2' |
	      'pipe' | 'alrm' | 'term' | 'stkflt' | 'chld' | 'cont' |
	      'stop' | 'stp' | 'ttin' | 'ttou' | 'urg' | 'xcpu' |
	      'xfsz' | 'vtalrm' | 'prof' | 'winch' | 'io' | 'pwr' |
	      'sys' | 'emt' | 'exists' | 'rtmin+0' ... 'rtmin+32'
            )

  SIGNAL PEER = 'peer' '=' AARE

eg.
  signal,                                 # allow all signals
  signal send set=(hup, kill) peer=foo,

Signed-off-by: John Johansen <john.johansen@canonical.com>
Acked-by: Seth Arnold <seth.arnold@canonical.com>
This commit is contained in:
John Johansen 2017-07-18 22:56:22 -07:00
parent c5561700c9
commit cd1dbf76b2
7 changed files with 231 additions and 0 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

7
security/apparmor/apparmorfs.c
View file

@ -32,6 +32,7 @@
#include "include/audit.h"
#include "include/context.h"
#include "include/crypto.h"
#include "include/ipc.h"
#include "include/policy_ns.h"
#include "include/label.h"
#include "include/policy.h"
@ -2129,6 +2130,11 @@ static struct aa_sfs_entry aa_sfs_entry_ptrace[] = {
{ }
};
static struct aa_sfs_entry aa_sfs_entry_signal[] = {
AA_SFS_FILE_STRING("mask", AA_SFS_SIG_MASK),
{ }
};
static struct aa_sfs_entry aa_sfs_entry_domain[] = {
AA_SFS_FILE_BOOLEAN("change_hat", 1),
AA_SFS_FILE_BOOLEAN("change_hatv", 1),
@ -2179,6 +2185,7 @@ static struct aa_sfs_entry aa_sfs_entry_features[] = {
AA_SFS_DIR("rlimit", aa_sfs_entry_rlimit),
AA_SFS_DIR("caps", aa_sfs_entry_caps),
AA_SFS_DIR("ptrace", aa_sfs_entry_ptrace),
AA_SFS_DIR("signal", aa_sfs_entry_signal),
AA_SFS_DIR("query", aa_sfs_entry_query),
{ }
};

1
security/apparmor/include/apparmor.h
View file

@ -28,6 +28,7 @@
#define AA_CLASS_RLIMITS 5
#define AA_CLASS_DOMAIN 6
#define AA_CLASS_PTRACE 9
#define AA_CLASS_SIGNAL 10
#define AA_CLASS_LABEL 16
#define AA_CLASS_LAST AA_CLASS_LABEL

2
security/apparmor/include/audit.h
View file

@ -86,6 +86,7 @@ enum audit_type {
#define OP_SHUTDOWN "socket_shutdown"
#define OP_PTRACE "ptrace"
#define OP_SIGNAL "signal"
#define OP_EXEC "exec"
@ -126,6 +127,7 @@ struct apparmor_audit_data {
long pos;
const char *ns;
} iface;
int signal;
struct {
int rlim;
unsigned long max;

6
security/apparmor/include/ipc.h
View file

@ -27,8 +27,14 @@ struct aa_profile;
#define AA_PTRACE_PERM_MASK (AA_PTRACE_READ | AA_PTRACE_TRACE | \
AA_MAY_BE_READ | AA_MAY_BE_TRACED)
#define AA_SIGNAL_PERM_MASK (MAY_READ | MAY_WRITE)
#define AA_SFS_SIG_MASK "hup int quit ill trap abrt bus fpe kill usr1 " \
"segv usr2 pipe alrm term stkflt chld cont stop stp ttin ttou urg " \
"xcpu xfsz vtalrm prof winch io pwr sys emt lost"
int aa_may_ptrace(struct aa_label *tracer, struct aa_label *tracee,
u32 request);
int aa_may_signal(struct aa_label *sender, struct aa_label *target, int sig);
#endif /* __AA_IPC_H */

95
security/apparmor/include/sig_names.h Normal file
View file

@ -0,0 +1,95 @@
#include <linux/signal.h>
#define SIGUNKNOWN 0
#define MAXMAPPED_SIG 35
/* provide a mapping of arch signal to internal signal # for mediation
* those that are always an alias SIGCLD for SIGCLHD and SIGPOLL for SIGIO
* map to the same entry those that may/or may not get a separate entry
*/
static const int sig_map[MAXMAPPED_SIG] = {
[0] = MAXMAPPED_SIG, /* existence test */
[SIGHUP] = 1,
[SIGINT] = 2,
[SIGQUIT] = 3,
[SIGILL] = 4,
[SIGTRAP] = 5, /* -, 5, - */
[SIGABRT] = 6, /* SIGIOT: -, 6, - */
[SIGBUS] = 7, /* 10, 7, 10 */
[SIGFPE] = 8,
[SIGKILL] = 9,
[SIGUSR1] = 10, /* 30, 10, 16 */
[SIGSEGV] = 11,
[SIGUSR2] = 12, /* 31, 12, 17 */
[SIGPIPE] = 13,
[SIGALRM] = 14,
[SIGTERM] = 15,
[SIGSTKFLT] = 16, /* -, 16, - */
[SIGCHLD] = 17, /* 20, 17, 18. SIGCHLD -, -, 18 */
[SIGCONT] = 18, /* 19, 18, 25 */
[SIGSTOP] = 19, /* 17, 19, 23 */
[SIGTSTP] = 20, /* 18, 20, 24 */
[SIGTTIN] = 21, /* 21, 21, 26 */
[SIGTTOU] = 22, /* 22, 22, 27 */
[SIGURG] = 23, /* 16, 23, 21 */
[SIGXCPU] = 24, /* 24, 24, 30 */
[SIGXFSZ] = 25, /* 25, 25, 31 */
[SIGVTALRM] = 26, /* 26, 26, 28 */
[SIGPROF] = 27, /* 27, 27, 29 */
[SIGWINCH] = 28, /* 28, 28, 20 */
[SIGIO] = 29, /* SIGPOLL: 23, 29, 22 */
[SIGPWR] = 30, /* 29, 30, 19. SIGINFO 29, -, - */
#ifdef SIGSYS
[SIGSYS] = 31, /* 12, 31, 12. often SIG LOST/UNUSED */
#endif
#ifdef SIGEMT
[SIGEMT] = 32, /* 7, - , 7 */
#endif
#if defined(SIGLOST) && SIGPWR != SIGLOST /* sparc */
[SIGLOST] = 33, /* unused on Linux */
#endif
#if defined(SIGLOST) && defined(SIGSYS) && SIGLOST != SIGSYS
[SIGUNUSED] = 34, /* -, 31, - */
#endif
};
/* this table is ordered post sig_map[sig] mapping */
static const char *const sig_names[MAXMAPPED_SIG + 1] = {
"unknown",
"hup",
"int",
"quit",
"ill",
"trap",
"abrt",
"bus",
"fpe",
"kill",
"usr1",
"segv",
"usr2",
"pipe",
"alrm",
"term",
"stkflt",
"chld",
"cont",
"stop",
"stp",
"ttin",
"ttou",
"urg",
"xcpu",
"xfsz",
"vtalrm",
"prof",
"winch",
"io",
"pwr",
"sys",
"emt",
"lost",
"unused",
"exists", /* always last existence test mapped to MAXMAPPED_SIG */
};

99
security/apparmor/ipc.c
View file

@ -20,6 +20,7 @@
#include "include/context.h"
#include "include/policy.h"
#include "include/ipc.h"
#include "include/sig_names.h"
/**
* audit_ptrace_mask - convert mask to permission string
@ -121,3 +122,101 @@ int aa_may_ptrace(struct aa_label *tracer, struct aa_label *tracee,
}
static inline int map_signal_num(int sig)
{
if (sig > SIGRTMAX)
return SIGUNKNOWN;
else if (sig >= SIGRTMIN)
return sig - SIGRTMIN + 128; /* rt sigs mapped to 128 */
else if (sig <= MAXMAPPED_SIG)
return sig_map[sig];
return SIGUNKNOWN;
}
/**
* audit_file_mask - convert mask to permission string
* @buffer: buffer to write string to (NOT NULL)
* @mask: permission mask to convert
*/
static void audit_signal_mask(struct audit_buffer *ab, u32 mask)
{
if (mask & MAY_READ)
audit_log_string(ab, "receive");
if (mask & MAY_WRITE)
audit_log_string(ab, "send");
}
/**
* audit_cb - call back for signal specific audit fields
* @ab: audit_buffer (NOT NULL)
* @va: audit struct to audit values of (NOT NULL)
*/
static void audit_signal_cb(struct audit_buffer *ab, void *va)
{
struct common_audit_data *sa = va;
if (aad(sa)->request & AA_SIGNAL_PERM_MASK) {
audit_log_format(ab, " requested_mask=");
audit_signal_mask(ab, aad(sa)->request);
if (aad(sa)->denied & AA_SIGNAL_PERM_MASK) {
audit_log_format(ab, " denied_mask=");
audit_signal_mask(ab, aad(sa)->denied);
}
}
if (aad(sa)->signal <= MAXMAPPED_SIG)
audit_log_format(ab, " signal=%s", sig_names[aad(sa)->signal]);
else
audit_log_format(ab, " signal=rtmin+%d",
aad(sa)->signal - 128);
audit_log_format(ab, " peer=");
aa_label_xaudit(ab, labels_ns(aad(sa)->label), aad(sa)->peer,
FLAGS_NONE, GFP_ATOMIC);
}
/* TODO: update to handle compound name&name2, conditionals */
static void profile_match_signal(struct aa_profile *profile, const char *label,
int signal, struct aa_perms *perms)
{
unsigned int state;
/* TODO: secondary cache check <profile, profile, perm> */
state = aa_dfa_next(profile->policy.dfa,
profile->policy.start[AA_CLASS_SIGNAL],
signal);
state = aa_dfa_match(profile->policy.dfa, state, label);
aa_compute_perms(profile->policy.dfa, state, perms);
}
static int profile_signal_perm(struct aa_profile *profile,
struct aa_profile *peer, u32 request,
struct common_audit_data *sa)
{
struct aa_perms perms;
if (profile_unconfined(profile) ||
!PROFILE_MEDIATES(profile, AA_CLASS_SIGNAL))
return 0;
aad(sa)->peer = &peer->label;
profile_match_signal(profile, peer->base.hname, aad(sa)->signal,
&perms);
aa_apply_modes_to_perms(profile, &perms);
return aa_check_perms(profile, &perms, request, sa, audit_signal_cb);
}
static int aa_signal_cross_perm(struct aa_profile *sender,
struct aa_profile *target,
struct common_audit_data *sa)
{
return xcheck(profile_signal_perm(sender, target, MAY_WRITE, sa),
profile_signal_perm(target, sender, MAY_READ, sa));
}
int aa_may_signal(struct aa_label *sender, struct aa_label *target, int sig)
{
DEFINE_AUDIT_DATA(sa, LSM_AUDIT_DATA_NONE, OP_SIGNAL);
aad(&sa)->signal = map_signal_num(sig);
return xcheck_labels_profiles(sender, target, aa_signal_cross_perm,
&sa);
}

21
security/apparmor/lsm.c
View file

@ -656,6 +656,26 @@ static int apparmor_task_setrlimit(struct task_struct *task,
return error;
}
static int apparmor_task_kill(struct task_struct *target, struct siginfo *info,
int sig, u32 secid)
{
struct aa_label *cl, *tl;
int error;
if (secid)
/* TODO: after secid to label mapping is done.
* Dealing with USB IO specific behavior
*/
return 0;
cl = __begin_current_label_crit_section();
tl = aa_get_task_label(target);
error = aa_may_signal(cl, tl, sig);
aa_put_label(tl);
__end_current_label_crit_section(cl);
return error;
}
static struct security_hook_list apparmor_hooks[] __lsm_ro_after_init = {
LSM_HOOK_INIT(ptrace_access_check, apparmor_ptrace_access_check),
LSM_HOOK_INIT(ptrace_traceme, apparmor_ptrace_traceme),
@ -697,6 +717,7 @@ static struct security_hook_list apparmor_hooks[] __lsm_ro_after_init = {
LSM_HOOK_INIT(bprm_secureexec, apparmor_bprm_secureexec),
LSM_HOOK_INIT(task_setrlimit, apparmor_task_setrlimit),
LSM_HOOK_INIT(task_kill, apparmor_task_kill),
};
/*