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Systemd/src/core/bpf-devices.c
Zbigniew Jędrzejewski-Szmek 124e05b3b6 core: move bpf devices implementation to bpf-devices.[ch] and rename 
The naming of the functions was a complete mess: the most specific functions
which don't know anything about cgroups had "cgroup_" prefix, while more
general functions which took a node path and a cgroup for reporting had no
prefix. Let's use "bpf_devices_" for the latter group, and "bpf_prog_*" for the
rest.

The main goal of this move is to split the implementation from the calling code
and add unit tests in a later patch.
2019-11-10 23:22:15 +01:00

420 lines
15 KiB
C
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/* SPDX-License-Identifier: LGPL-2.1+ */
#include <fnmatch.h>
#include <linux/bpf_insn.h>
#include "bpf-devices.h"
#include "bpf-program.h"
#include "fd-util.h"
#include "fileio.h"
#include "parse-util.h"
#include "stat-util.h"
#include "stdio-util.h"
#include "string-util.h"
#define PASS_JUMP_OFF 4096
static int bpf_access_type(const char *acc) {
int r = 0;
assert(acc);
for (; *acc; acc++)
switch(*acc) {
case 'r':
r |= BPF_DEVCG_ACC_READ;
break;
case 'w':
r |= BPF_DEVCG_ACC_WRITE;
break;
case 'm':
r |= BPF_DEVCG_ACC_MKNOD;
break;
default:
return -EINVAL;
}
return r;
}
static int bpf_prog_whitelist_device(BPFProgram *prog, int type, int major, int minor, const char *acc) {
int r, access;
assert(prog);
assert(acc);
access = bpf_access_type(acc);
if (access <= 0)
return -EINVAL;
const struct bpf_insn insn[] = {
BPF_JMP_IMM(BPF_JNE, BPF_REG_2, type, 6), /* compare device type */
BPF_MOV32_REG(BPF_REG_1, BPF_REG_3), /* calculate access type */
BPF_ALU32_IMM(BPF_AND, BPF_REG_1, access),
BPF_JMP_REG(BPF_JNE, BPF_REG_1, BPF_REG_3, 3), /* compare access type */
BPF_JMP_IMM(BPF_JNE, BPF_REG_4, major, 2), /* compare major */
BPF_JMP_IMM(BPF_JNE, BPF_REG_5, minor, 1), /* compare minor */
BPF_JMP_A(PASS_JUMP_OFF), /* jump to PASS */
};
r = bpf_program_add_instructions(prog, insn, ELEMENTSOF(insn));
if (r < 0)
log_error_errno(r, "Extending device control BPF program failed: %m");
return r;
}
static int bpf_prog_whitelist_major(BPFProgram *prog, int type, int major, const char *acc) {
int r, access;
assert(prog);
assert(acc);
access = bpf_access_type(acc);
if (access <= 0)
return -EINVAL;
const struct bpf_insn insn[] = {
BPF_JMP_IMM(BPF_JNE, BPF_REG_2, type, 5), /* compare device type */
BPF_MOV32_REG(BPF_REG_1, BPF_REG_3), /* calculate access type */
BPF_ALU32_IMM(BPF_AND, BPF_REG_1, access),
BPF_JMP_REG(BPF_JNE, BPF_REG_1, BPF_REG_3, 2), /* compare access type */
BPF_JMP_IMM(BPF_JNE, BPF_REG_4, major, 1), /* compare major */
BPF_JMP_A(PASS_JUMP_OFF), /* jump to PASS */
};
r = bpf_program_add_instructions(prog, insn, ELEMENTSOF(insn));
if (r < 0)
log_error_errno(r, "Extending device control BPF program failed: %m");
return r;
}
static int bpf_prog_whitelist_class(BPFProgram *prog, int type, const char *acc) {
int r, access;
assert(prog);
assert(acc);
access = bpf_access_type(acc);
if (access <= 0)
return -EINVAL;
const struct bpf_insn insn[] = {
BPF_JMP_IMM(BPF_JNE, BPF_REG_2, type, 5), /* compare device type */
BPF_MOV32_REG(BPF_REG_1, BPF_REG_3), /* calculate access type */
BPF_ALU32_IMM(BPF_AND, BPF_REG_1, access),
BPF_JMP_REG(BPF_JNE, BPF_REG_1, BPF_REG_3, 1), /* compare access type */
BPF_JMP_A(PASS_JUMP_OFF), /* jump to PASS */
};
r = bpf_program_add_instructions(prog, insn, ELEMENTSOF(insn));
if (r < 0)
log_error_errno(r, "Extending device control BPF program failed: %m");
return r;
}
int bpf_devices_cgroup_init(BPFProgram **ret, CGroupDevicePolicy policy, bool whitelist) {
const struct bpf_insn pre_insn[] = {
/* load device type to r2 */
BPF_LDX_MEM(BPF_H, BPF_REG_2, BPF_REG_1,
offsetof(struct bpf_cgroup_dev_ctx, access_type)),
/* load access type to r3 */
BPF_LDX_MEM(BPF_W, BPF_REG_3, BPF_REG_1,
offsetof(struct bpf_cgroup_dev_ctx, access_type)),
BPF_ALU32_IMM(BPF_RSH, BPF_REG_3, 16),
/* load major number to r4 */
BPF_LDX_MEM(BPF_W, BPF_REG_4, BPF_REG_1,
offsetof(struct bpf_cgroup_dev_ctx, major)),
/* load minor number to r5 */
BPF_LDX_MEM(BPF_W, BPF_REG_5, BPF_REG_1,
offsetof(struct bpf_cgroup_dev_ctx, minor)),
};
_cleanup_(bpf_program_unrefp) BPFProgram *prog = NULL;
int r;
assert(ret);
if (policy == CGROUP_DEVICE_POLICY_AUTO && !whitelist)
return 0;
r = bpf_program_new(BPF_PROG_TYPE_CGROUP_DEVICE, &prog);
if (r < 0)
return log_error_errno(r, "Loading device control BPF program failed: %m");
if (policy == CGROUP_DEVICE_POLICY_CLOSED || whitelist) {
r = bpf_program_add_instructions(prog, pre_insn, ELEMENTSOF(pre_insn));
if (r < 0)
return log_error_errno(r, "Extending device control BPF program failed: %m");
}
*ret = TAKE_PTR(prog);
return 0;
}
int bpf_devices_apply_policy(Unit *u, BPFProgram *prog, CGroupDevicePolicy policy, bool whitelist) {
_cleanup_free_ char *path = NULL;
int r;
if (!prog) {
/* Remove existing program. */
u->bpf_device_control_installed = bpf_program_unref(u->bpf_device_control_installed);
return 0;
}
const bool deny_everything = policy == CGROUP_DEVICE_POLICY_STRICT && !whitelist;
const struct bpf_insn post_insn[] = {
/* return DENY */
BPF_MOV64_IMM(BPF_REG_0, 0),
BPF_JMP_A(1),
};
const struct bpf_insn exit_insn[] = {
/* finally return DENY if deny_everything else ALLOW */
BPF_MOV64_IMM(BPF_REG_0, deny_everything ? 0 : 1),
BPF_EXIT_INSN()
};
if (!deny_everything) {
r = bpf_program_add_instructions(prog, post_insn, ELEMENTSOF(post_insn));
if (r < 0)
return log_error_errno(r, "Extending device control BPF program failed: %m");
/* Fixup PASS_JUMP_OFF jump offsets. */
for (size_t off = 0; off < prog->n_instructions; off++) {
struct bpf_insn *ins = &prog->instructions[off];
if (ins->code == (BPF_JMP | BPF_JA) && ins->off == PASS_JUMP_OFF)
ins->off = prog->n_instructions - off - 1;
}
}
r = bpf_program_add_instructions(prog, exit_insn, ELEMENTSOF(exit_insn));
if (r < 0)
return log_error_errno(r, "Extending device control BPF program failed: %m");
r = cg_get_path(SYSTEMD_CGROUP_CONTROLLER, u->cgroup_path, NULL, &path);
if (r < 0)
return log_error_errno(r, "Failed to determine cgroup path: %m");
r = bpf_program_cgroup_attach(prog, BPF_CGROUP_DEVICE, path, BPF_F_ALLOW_MULTI);
if (r < 0)
return log_error_errno(r, "Attaching device control BPF program to cgroup %s failed: %m", path);
/* Unref the old BPF program (which will implicitly detach it) right before attaching the new program. */
u->bpf_device_control_installed = bpf_program_unref(u->bpf_device_control_installed);
/* Remember that this BPF program is installed now. */
u->bpf_device_control_installed = bpf_program_ref(prog);
return 0;
}
int bpf_devices_supported(void) {
const struct bpf_insn trivial[] = {
BPF_MOV64_IMM(BPF_REG_0, 1),
BPF_EXIT_INSN()
};
_cleanup_(bpf_program_unrefp) BPFProgram *program = NULL;
static int supported = -1;
int r;
/* Checks whether BPF device controller is supported. For this, we check five things:
*
* a) whether we are privileged
* b) whether the unified hierarchy is being used
* c) the BPF implementation in the kernel supports BPF_PROG_TYPE_CGROUP_DEVICE programs, which we require
*/
if (supported >= 0)
return supported;
if (geteuid() != 0) {
log_debug("Not enough privileges, BPF device control is not supported.");
return supported = 0;
}
r = cg_unified_controller(SYSTEMD_CGROUP_CONTROLLER);
if (r < 0)
return log_error_errno(r, "Can't determine whether the unified hierarchy is used: %m");
if (r == 0) {
log_debug("Not running with unified cgroups, BPF device control is not supported.");
return supported = 0;
}
r = bpf_program_new(BPF_PROG_TYPE_CGROUP_DEVICE, &program);
if (r < 0) {
log_debug_errno(r, "Can't allocate CGROUP DEVICE BPF program, BPF device control is not supported: %m");
return supported = 0;
}
r = bpf_program_add_instructions(program, trivial, ELEMENTSOF(trivial));
if (r < 0) {
log_debug_errno(r, "Can't add trivial instructions to CGROUP DEVICE BPF program, BPF device control is not supported: %m");
return supported = 0;
}
r = bpf_program_load_kernel(program, NULL, 0);
if (r < 0) {
log_debug_errno(r, "Can't load kernel CGROUP DEVICE BPF program, BPF device control is not supported: %m");
return supported = 0;
}
return supported = 1;
}
static int whitelist_device_pattern(BPFProgram *prog, const char *path, char type, const unsigned *maj, const unsigned *min, const char *acc) {
assert(IN_SET(type, 'b', 'c'));
if (cg_all_unified() > 0) {
if (!prog)
return 0;
const int bpf_type = type == 'c' ? BPF_DEVCG_DEV_CHAR : BPF_DEVCG_DEV_BLOCK;
if (maj && min)
return bpf_prog_whitelist_device(prog, bpf_type, *maj, *min, acc);
else if (maj)
return bpf_prog_whitelist_major(prog, bpf_type, *maj, acc);
else
return bpf_prog_whitelist_class(prog, bpf_type, acc);
} else {
char buf[2+DECIMAL_STR_MAX(unsigned)*2+2+4];
int r;
if (maj && min)
xsprintf(buf, "%c %u:%u %s", type, *maj, *min, acc);
else if (maj)
xsprintf(buf, "%c %u:* %s", type, *maj, acc);
else
xsprintf(buf, "%c *:* %s", type, acc);
/* Changing the devices list of a populated cgroup might result in EINVAL, hence ignore
* EINVAL here. */
r = cg_set_attribute("devices", path, "devices.allow", buf);
if (r < 0)
log_full_errno(IN_SET(r, -ENOENT, -EROFS, -EINVAL, -EACCES, -EPERM) ? LOG_DEBUG : LOG_WARNING,
r, "Failed to set devices.allow on %s: %m", path);
return r;
}
}
int bpf_devices_whitelist_device(BPFProgram *prog, const char *path, const char *node, const char *acc) {
mode_t mode;
dev_t rdev;
int r;
assert(path);
assert(acc);
assert(strlen(acc) <= 3);
/* Some special handling for /dev/block/%u:%u, /dev/char/%u:%u, /run/systemd/inaccessible/chr and
* /run/systemd/inaccessible/blk paths. Instead of stat()ing these we parse out the major/minor directly. This
* means clients can use these path without the device node actually around */
r = device_path_parse_major_minor(node, &mode, &rdev);
if (r < 0) {
if (r != -ENODEV)
return log_warning_errno(r, "Couldn't parse major/minor from device path '%s': %m", node);
struct stat st;
if (stat(node, &st) < 0)
return log_warning_errno(errno, "Couldn't stat device %s: %m", node);
if (!S_ISCHR(st.st_mode) && !S_ISBLK(st.st_mode))
return log_warning_errno(SYNTHETIC_ERRNO(ENODEV), "%s is not a device.", node);
mode = st.st_mode;
rdev = (dev_t) st.st_rdev;
}
unsigned maj = major(rdev), min = minor(rdev);
return whitelist_device_pattern(prog, path, S_ISCHR(mode) ? 'c' : 'b', &maj, &min, acc);
}
int bpf_devices_whitelist_major(BPFProgram *prog, const char *path, const char *name, char type, const char *acc) {
unsigned maj;
int r;
assert(path);
assert(acc);
assert(IN_SET(type, 'b', 'c'));
if (streq(name, "*"))
/* If the name is a wildcard, then apply this list to all devices of this type */
return whitelist_device_pattern(prog, path, type, NULL, NULL, acc);
if (safe_atou(name, &maj) >= 0 && DEVICE_MAJOR_VALID(maj))
/* The name is numeric and suitable as major. In that case, let's take its major, and create
* the entry directly. */
return whitelist_device_pattern(prog, path, type, &maj, NULL, acc);
_cleanup_fclose_ FILE *f = NULL;
bool good = false;
f = fopen("/proc/devices", "re");
if (!f)
return log_warning_errno(errno, "Cannot open /proc/devices to resolve %s: %m", name);
for (;;) {
_cleanup_free_ char *line = NULL;
char *w, *p;
r = read_line(f, LONG_LINE_MAX, &line);
if (r < 0)
return log_warning_errno(r, "Failed to read /proc/devices: %m");
if (r == 0)
break;
if (type == 'c' && streq(line, "Character devices:")) {
good = true;
continue;
}
if (type == 'b' && streq(line, "Block devices:")) {
good = true;
continue;
}
if (isempty(line)) {
good = false;
continue;
}
if (!good)
continue;
p = strstrip(line);
w = strpbrk(p, WHITESPACE);
if (!w)
continue;
*w = 0;
r = safe_atou(p, &maj);
if (r < 0)
continue;
if (maj <= 0)
continue;
w++;
w += strspn(w, WHITESPACE);
if (fnmatch(name, w, 0) != 0)
continue;
(void) whitelist_device_pattern(prog, path, type, &maj, NULL, acc);
}
return 0;
}
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