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/*
* Copyright (C) 2014-2018 Firejail Authors
*
* This file is part of firejail project
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License along
* with this program; if not, write to the Free Software Foundation, Inc.,
* 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
*/
#include "fsec_optimize.h"
// From /usr/include/linux/filter.h
//struct sock_filter { /* Filter block */
// __u16 code; /* Actual filter code */
// __u8 jt; /* Jump true */
// __u8 jf; /* Jump false */
// __u32 k; /* Generic multiuse field */
//};
#define LIMIT_BLACKLISTS 4 // we optimize blacklists only if we have more than
static inline int is_blacklist(struct sock_filter *bpf) {
if (bpf->code == BPF_JMP + BPF_JEQ + BPF_K &&
(bpf + 1)->code == BPF_RET + BPF_K &&
(bpf + 1)->k == SECCOMP_RET_KILL )
return 1;
return 0;
}
static int count_blacklists(struct sock_filter *filter, int entries) {
int cnt = 0;
int i;
for (i = 0; i < (entries - 1); i++, filter++) { // is_blacklist works on two consecutive lines; using entries - 1
if (is_blacklist(filter))
cnt++;
}
return cnt;
}
typedef struct {
int to_remove;
int to_fix_jumps;
} Action;
static int optimize_blacklists(struct sock_filter *filter, int entries) {
assert(entries);
assert(filter);
int i;
int j;
// step1: extract information
Action action[entries];
memset(&action[0], 0, sizeof(Action) * entries);
int remove_cnt = 0;
for (i = 0; i < (entries - 1); i++) { // is_blacklist works on two consecutive lines; using entries - 1
if (is_blacklist(filter + i)) {
action[i]. to_fix_jumps = 1;
i++;
action[i].to_remove = 1;
remove_cnt++;
}
}
// step2: remove lines
struct sock_filter *filter_step2 = duplicate(filter, entries);
Action action_step2[entries];
memset(&action_step2[0], 0, sizeof(Action) * entries);
for (i = 0, j = 0; i < entries; i++) {
if (!action[i].to_remove) {
memcpy(&filter_step2[j], &filter[i], sizeof(struct sock_filter));
memcpy(&action_step2[j], &action[i], sizeof(Action));
j++;
}
else {
// do nothing, we are removing this line
}
}
// step 3: add the new ret KILL, and recalculate entries
filter_step2[j].code = BPF_RET + BPF_K;
filter_step2[j].k == SECCOMP_RET_KILL;
entries = j + 1;
// step 4: recalculate jumps
for (i = 0; i < entries; i++) {
if (action_step2[i].to_fix_jumps) {
filter_step2[i].jt = entries - i - 2;
filter_step2[i].jf = 0;
}
}
// update
memcpy(filter, filter_step2, entries * sizeof(struct sock_filter));
free(filter_step2);
return entries;
}
int optimize(struct sock_filter *filter, int entries) {
assert(filter);
assert(entries);
//**********************************
// optimize blacklist statements
//**********************************
// count "ret KILL"
int cnt = count_blacklists(filter, entries);
if (cnt > LIMIT_BLACKLISTS)
entries = optimize_blacklists(filter, entries);
return entries;
}
struct sock_filter *duplicate(struct sock_filter *filter, int entries) {
int len = sizeof(struct sock_filter) * entries;
struct sock_filter *rv = malloc(len);
if (!rv) {
errExit("malloc");
exit(1);
}
memcpy(rv, filter, len);
return rv;
}
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