strace/bpf_filter.c
Dmitry V. Levin 899220d28d Generalize seccomp filter parser
Linux socket filter uses almost the same classic BPF as seccomp filter,
The only difference noticeable from strace PoV is the meaning of generic
multiuse field.

Transform the parser of seccomp filters to a more generic parser
of classic BPF, parametrized with a method of parsing the generic
multiuse field in BPF_STMT.

* bpf_filter.c: New file.
* bpf_filter.h: Likewise.
* bpf_fprog.h: Likewise.
* bpf_seccomp_filter.c: Likewise.
* fetch_bpf_fprog.c: Likewise.
* fetch_seccomp_fprog.c: Remove.
* seccomp_fprog.h: Likewise.
* Makefile.am (strace_SOURCES): Add bpf_filter.c, bpf_filter.h,
bpf_fprog.h, bpf_seccomp_filter.c, and fetch_bpf_fprog.c.
Remove fetch_seccomp_fprog.c and seccomp_fprog.h.
* seccomp.c: Do not include linux/filter.h and xlat header files.
Do not define SECCOMP_RET_ACTION.
(bpf_filter, decode_bpf_code, decode_bpf_stmt, decode_bpf_jump,
print_bpf_filter, print_seccomp_fprog, print_seccomp_filter): Remove.
* defs.h (print_seccomp_filter): Rename to decode_seccomp_fprog.
(SYS_FUNC(seccomp)): Replace print_seccomp_filter
with decode_seccomp_fprog.
* prctl.c (SYS_FUNC(prctl)): Likewise.
2017-07-08 01:49:00 +00:00

171 lines
4.6 KiB
C

/*
* Decoder of classic BPF programs.
*
* Copyright (c) 2015-2017 Dmitry V. Levin <ldv@altlinux.org>
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 3. The name of the author may not be used to endorse or promote products
* derived from this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
* IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
* IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
* NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
* THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
#include "defs.h"
#include "bpf_filter.h"
#include "bpf_fprog.h"
#include <linux/filter.h>
#include "xlat/bpf_class.h"
#include "xlat/bpf_miscop.h"
#include "xlat/bpf_mode.h"
#include "xlat/bpf_op_alu.h"
#include "xlat/bpf_op_jmp.h"
#include "xlat/bpf_rval.h"
#include "xlat/bpf_size.h"
#include "xlat/bpf_src.h"
static void
print_bpf_filter_code(const uint16_t code)
{
uint16_t i = code & ~BPF_CLASS(code);
printxval(bpf_class, BPF_CLASS(code), "BPF_???");
switch (BPF_CLASS(code)) {
case BPF_LD:
case BPF_LDX:
tprints("|");
printxval(bpf_size, BPF_SIZE(code), "BPF_???");
tprints("|");
printxval(bpf_mode, BPF_MODE(code), "BPF_???");
break;
case BPF_ST:
case BPF_STX:
if (i) {
tprintf("|%#x", i);
tprints_comment("BPF_???");
}
break;
case BPF_ALU:
tprints("|");
printxval(bpf_src, BPF_SRC(code), "BPF_???");
tprints("|");
printxval(bpf_op_alu, BPF_OP(code), "BPF_???");
break;
case BPF_JMP:
tprints("|");
printxval(bpf_src, BPF_SRC(code), "BPF_???");
tprints("|");
printxval(bpf_op_jmp, BPF_OP(code), "BPF_???");
break;
case BPF_RET:
tprints("|");
printxval(bpf_rval, BPF_RVAL(code), "BPF_???");
i &= ~BPF_RVAL(code);
if (i) {
tprintf("|%#x", i);
tprints_comment("BPF_???");
}
break;
case BPF_MISC:
tprints("|");
printxval(bpf_miscop, BPF_MISCOP(code), "BPF_???");
i &= ~BPF_MISCOP(code);
if (i) {
tprintf("|%#x", i);
tprints_comment("BPF_???");
}
break;
}
}
static void
print_bpf_filter_stmt(const struct bpf_filter_block *const filter,
const print_bpf_filter_fn print_k)
{
tprints("BPF_STMT(");
print_bpf_filter_code(filter->code);
tprints(", ");
if (!print_k || !print_k(filter))
tprintf("%#x", filter->k);
tprints(")");
}
static void
print_bpf_filter_jump(const struct bpf_filter_block *const filter)
{
tprints("BPF_JUMP(");
print_bpf_filter_code(filter->code);
tprintf(", %#x, %#x, %#x)", filter->k, filter->jt, filter->jf);
}
struct bpf_filter_block_data {
const print_bpf_filter_fn fn;
unsigned int count;
};
static bool
print_bpf_filter_block(struct tcb *const tcp, void *const elem_buf,
const size_t elem_size, void *const data)
{
const struct bpf_filter_block *const filter = elem_buf;
struct bpf_filter_block_data *const fbd = data;
if (fbd->count++ >= BPF_MAXINSNS) {
tprints("...");
return false;
}
if (filter->jt || filter->jf)
print_bpf_filter_jump(filter);
else
print_bpf_filter_stmt(filter, fbd->fn);
return true;
}
void
print_bpf_fprog(struct tcb *const tcp, const kernel_ulong_t addr,
const unsigned short len, const print_bpf_filter_fn print_k)
{
if (abbrev(tcp)) {
printaddr(addr);
} else {
struct bpf_filter_block_data fbd = { .fn = print_k };
struct bpf_filter_block filter;
print_array(tcp, addr, len, &filter, sizeof(filter),
umoven_or_printaddr, print_bpf_filter_block, &fbd);
}
}
void
decode_bpf_fprog(struct tcb *const tcp, const kernel_ulong_t addr,
const print_bpf_filter_fn print_k)
{
struct bpf_fprog fprog;
if (fetch_bpf_fprog(tcp, addr, &fprog)) {
tprintf("{len=%hu, filter=", fprog.len);
print_bpf_fprog(tcp, fprog.filter, fprog.len, print_k);
tprints("}");
}
}