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/*
* Minimal handling of Linux kernel capabilities
*
* Copyright 2000-2023 Willy Tarreau <w@1wt.eu>
*
* 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.
*
*/
/* Depending on distros, some have capset(), others use the more complicated
* libcap. Let's stick to what we need and the kernel documents (capset).
* Note that prctl is needed here.
*/
#include <linux/capability.h>
#include <sys/prctl.h>
#include <errno.h>
#include <unistd.h>
#include <syscall.h>
#include <haproxy/api.h>
#include <haproxy/cfgparse.h>
#include <haproxy/errors.h>
#include <haproxy/tools.h>
/* supported names, zero-terminated */
static const struct {
int cap;
const char *name;
} known_caps[] = {
#ifdef CAP_NET_RAW
{ CAP_NET_RAW, "cap_net_raw" },
#endif
#ifdef CAP_NET_ADMIN
{ CAP_NET_ADMIN, "cap_net_admin" },
#endif
#ifdef CAP_NET_BIND_SERVICE
{ CAP_NET_BIND_SERVICE, "cap_net_bind_service" },
#endif
/* must be last */
{ 0, 0 }
};
/* provided by sys/capability.h on some distros */
static inline int capset(cap_user_header_t hdrp, const cap_user_data_t datap)
{
return syscall(SYS_capset, hdrp, datap);
}
/* defaults to zero, i.e. we don't keep any cap after setuid() */
static uint32_t caplist;
/* try to apply capabilities before switching UID from <from_uid> to <to_uid>.
* In practice we need to do this in 4 steps:
* - set PR_SET_KEEPCAPS to preserve caps across the final setuid()
* - set the effective and permitted caps ;
* - switch euid to non-zero
* - set the effective and permitted caps again
* - then the caller can safely call setuid()
* We don't do this if the current euid is not zero or if the target uid
* is zero. Returns >=0 on success, negative on failure. Alerts or warnings
* may be emitted.
*/
int prepare_caps_for_setuid(int from_uid, int to_uid)
{
struct __user_cap_data_struct cap_data = { };
struct __user_cap_header_struct cap_hdr = {
.pid = 0, /* current process */
.version = _LINUX_CAPABILITY_VERSION_1,
};
if (from_uid != 0)
return 0;
if (!to_uid)
return 0;
if (!caplist)
return 0;
if (prctl(PR_SET_KEEPCAPS, 1) == -1) {
ha_alert("Failed to preserve capabilities using prctl(): %s\n", strerror(errno));
return -1;
}
cap_data.effective = cap_data.permitted = caplist | (1 << CAP_SETUID);
if (capset(&cap_hdr, &cap_data) == -1) {
ha_alert("Failed to preset the capabilities to preserve using capset(): %s\n", strerror(errno));
return -1;
}
if (seteuid(to_uid) == -1) {
ha_alert("Failed to set effective uid to %d: %s\n", to_uid, strerror(errno));
return -1;
}
cap_data.effective = cap_data.permitted = caplist | (1 << CAP_SETUID);
if (capset(&cap_hdr, &cap_data) == -1) {
ha_alert("Failed to set the final capabilities using capset(): %s\n", strerror(errno));
return -1;
}
/* all's good */
return 0;
}
/* finalize the capabilities after setuid(). The most important is to drop the
* CAP_SET_SETUID capability, which would otherwise allow to switch back to any
* UID and recover everything.
*/
int finalize_caps_after_setuid(int from_uid, int to_uid)
{
struct __user_cap_data_struct cap_data = { };
struct __user_cap_header_struct cap_hdr = {
.pid = 0, /* current process */
.version = _LINUX_CAPABILITY_VERSION_1,
};
if (from_uid != 0)
return 0;
if (!to_uid)
return 0;
if (!caplist)
return 0;
cap_data.effective = cap_data.permitted = caplist;
if (capset(&cap_hdr, &cap_data) == -1) {
ha_alert("Failed to drop the setuid capability using capset(): %s\n", strerror(errno));
return -1;
}
/* all's good */
return 0;
}
/* parse the "setcap" global keyword. Returns -1 on failure, 0 on success. */
static int cfg_parse_global_setcap(char **args, int section_type,
struct proxy *curpx, const struct proxy *defpx,
const char *file, int line, char **err)
{
char *name = args[1];
char *next;
uint32_t caps = 0;
int id;
if (!*name) {
memprintf(err, "'%s' : missing capability name(s). ", args[0]);
goto dump_caps;
}
while (name && *name) {
next = strchr(name, ',');
if (next)
*(next++) = '\0';
for (id = 0; known_caps[id].cap; id++) {
if (strcmp(name, known_caps[id].name) == 0) {
caps |= 1U << known_caps[id].cap;
break;
}
}
if (!known_caps[id].cap) {
memprintf(err, "'%s' : unsupported capability '%s'. ", args[0], args[1]);
goto dump_caps;
}
name = next;
}
caplist |= caps;
return 0;
dump_caps:
memprintf(err, "%s Supported ones are: ", *err);
for (id = 0; known_caps[id].cap; id++)
memprintf(err, "%s%s%s%s", *err,
id ? known_caps[id+1].cap ? ", " : " and " : "",
known_caps[id].name, known_caps[id+1].cap ? "" : ".");
return -1;
}
static struct cfg_kw_list cfg_kws = {ILH, {
{ CFG_GLOBAL, "setcap", cfg_parse_global_setcap },
{ 0, NULL, NULL }
}};
INITCALL1(STG_REGISTER, cfg_register_keywords, &cfg_kws);
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