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qemu/tools/virtiofsd/helper.c
Stefan Hajnoczi 8c1d353d10 virtiofsd: stay below fs.file-max sysctl value (CVE-2020-10717) 
The system-wide fs.file-max sysctl value determines how many files can
be open.  It defaults to a value calculated based on the machine's RAM
size.  Previously virtiofsd would try to set RLIMIT_NOFILE to 1,000,000
and this allowed the FUSE client to exhaust the number of open files
system-wide on Linux hosts with less than 10 GB of RAM!

Take fs.file-max into account when choosing the default RLIMIT_NOFILE
value.

Fixes: CVE-2020-10717
Reported-by: Yuval Avrahami <yavrahami@paloaltonetworks.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Message-Id: <20200501140644.220940-3-stefanha@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
2020-05-01 18:41:56 +01:00

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/*
* FUSE: Filesystem in Userspace
* Copyright (C) 2001-2007 Miklos Szeredi <miklos@szeredi.hu>
*
* Helper functions to create (simple) standalone programs. With the
* aid of these functions it should be possible to create full FUSE
* file system by implementing nothing but the request handlers.
* This program can be distributed under the terms of the GNU LGPLv2.
* See the file COPYING.LIB.
*/
#include "qemu/osdep.h"
#include "fuse_i.h"
#include "fuse_lowlevel.h"
#include "fuse_misc.h"
#include "fuse_opt.h"
#include <errno.h>
#include <limits.h>
#include <stddef.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/param.h>
#include <sys/time.h>
#include <sys/resource.h>
#include <unistd.h>
#define FUSE_HELPER_OPT(t, p) \
{ \
t, offsetof(struct fuse_cmdline_opts, p), 1 \
}
#define FUSE_HELPER_OPT_VALUE(t, p, v) \
{ \
t, offsetof(struct fuse_cmdline_opts, p), v \
}
static const struct fuse_opt fuse_helper_opts[] = {
FUSE_HELPER_OPT("-h", show_help),
FUSE_HELPER_OPT("--help", show_help),
FUSE_HELPER_OPT("-V", show_version),
FUSE_HELPER_OPT("--version", show_version),
FUSE_HELPER_OPT("--print-capabilities", print_capabilities),
FUSE_HELPER_OPT("-d", debug),
FUSE_HELPER_OPT("debug", debug),
FUSE_HELPER_OPT("-d", foreground),
FUSE_HELPER_OPT("debug", foreground),
FUSE_OPT_KEY("-d", FUSE_OPT_KEY_KEEP),
FUSE_OPT_KEY("debug", FUSE_OPT_KEY_KEEP),
FUSE_HELPER_OPT("-f", foreground),
FUSE_HELPER_OPT_VALUE("--daemonize", foreground, 0),
FUSE_HELPER_OPT("fsname=", nodefault_subtype),
FUSE_OPT_KEY("fsname=", FUSE_OPT_KEY_KEEP),
FUSE_HELPER_OPT("subtype=", nodefault_subtype),
FUSE_OPT_KEY("subtype=", FUSE_OPT_KEY_KEEP),
FUSE_HELPER_OPT("max_idle_threads=%u", max_idle_threads),
FUSE_HELPER_OPT("--rlimit-nofile=%lu", rlimit_nofile),
FUSE_HELPER_OPT("--syslog", syslog),
FUSE_HELPER_OPT_VALUE("log_level=debug", log_level, FUSE_LOG_DEBUG),
FUSE_HELPER_OPT_VALUE("log_level=info", log_level, FUSE_LOG_INFO),
FUSE_HELPER_OPT_VALUE("log_level=warn", log_level, FUSE_LOG_WARNING),
FUSE_HELPER_OPT_VALUE("log_level=err", log_level, FUSE_LOG_ERR),
FUSE_OPT_END
};
struct fuse_conn_info_opts {
int atomic_o_trunc;
int no_remote_posix_lock;
int no_remote_flock;
int splice_write;
int splice_move;
int splice_read;
int no_splice_write;
int no_splice_move;
int no_splice_read;
int auto_inval_data;
int no_auto_inval_data;
int no_readdirplus;
int no_readdirplus_auto;
int async_dio;
int no_async_dio;
int writeback_cache;
int no_writeback_cache;
int async_read;
int sync_read;
unsigned max_write;
unsigned max_readahead;
unsigned max_background;
unsigned congestion_threshold;
unsigned time_gran;
int set_max_write;
int set_max_readahead;
int set_max_background;
int set_congestion_threshold;
int set_time_gran;
};
#define CONN_OPTION(t, p, v) \
{ \
t, offsetof(struct fuse_conn_info_opts, p), v \
}
static const struct fuse_opt conn_info_opt_spec[] = {
CONN_OPTION("max_write=%u", max_write, 0),
CONN_OPTION("max_write=", set_max_write, 1),
CONN_OPTION("max_readahead=%u", max_readahead, 0),
CONN_OPTION("max_readahead=", set_max_readahead, 1),
CONN_OPTION("max_background=%u", max_background, 0),
CONN_OPTION("max_background=", set_max_background, 1),
CONN_OPTION("congestion_threshold=%u", congestion_threshold, 0),
CONN_OPTION("congestion_threshold=", set_congestion_threshold, 1),
CONN_OPTION("sync_read", sync_read, 1),
CONN_OPTION("async_read", async_read, 1),
CONN_OPTION("atomic_o_trunc", atomic_o_trunc, 1),
CONN_OPTION("no_remote_lock", no_remote_posix_lock, 1),
CONN_OPTION("no_remote_lock", no_remote_flock, 1),
CONN_OPTION("no_remote_flock", no_remote_flock, 1),
CONN_OPTION("no_remote_posix_lock", no_remote_posix_lock, 1),
CONN_OPTION("splice_write", splice_write, 1),
CONN_OPTION("no_splice_write", no_splice_write, 1),
CONN_OPTION("splice_move", splice_move, 1),
CONN_OPTION("no_splice_move", no_splice_move, 1),
CONN_OPTION("splice_read", splice_read, 1),
CONN_OPTION("no_splice_read", no_splice_read, 1),
CONN_OPTION("auto_inval_data", auto_inval_data, 1),
CONN_OPTION("no_auto_inval_data", no_auto_inval_data, 1),
CONN_OPTION("readdirplus=no", no_readdirplus, 1),
CONN_OPTION("readdirplus=yes", no_readdirplus, 0),
CONN_OPTION("readdirplus=yes", no_readdirplus_auto, 1),
CONN_OPTION("readdirplus=auto", no_readdirplus, 0),
CONN_OPTION("readdirplus=auto", no_readdirplus_auto, 0),
CONN_OPTION("async_dio", async_dio, 1),
CONN_OPTION("no_async_dio", no_async_dio, 1),
CONN_OPTION("writeback_cache", writeback_cache, 1),
CONN_OPTION("no_writeback_cache", no_writeback_cache, 1),
CONN_OPTION("time_gran=%u", time_gran, 0),
CONN_OPTION("time_gran=", set_time_gran, 1),
FUSE_OPT_END
};
void fuse_cmdline_help(void)
{
printf(" -h --help print help\n"
" -V --version print version\n"
" --print-capabilities print vhost-user.json\n"
" -d -o debug enable debug output (implies -f)\n"
" --syslog log to syslog (default stderr)\n"
" -f foreground operation\n"
" --daemonize run in background\n"
" -o cache=<mode> cache mode. could be one of \"auto, "
"always, none\"\n"
" default: auto\n"
" -o flock|no_flock enable/disable flock\n"
" default: no_flock\n"
" -o log_level=<level> log level, default to \"info\"\n"
" level could be one of \"debug, "
"info, warn, err\"\n"
" -o max_idle_threads the maximum number of idle worker "
"threads\n"
" allowed (default: 10)\n"
" -o norace disable racy fallback\n"
" default: false\n"
" -o posix_lock|no_posix_lock\n"
" enable/disable remote posix lock\n"
" default: posix_lock\n"
" -o readdirplus|no_readdirplus\n"
" enable/disable readirplus\n"
" default: readdirplus except with "
"cache=none\n"
" -o timeout=<number> I/O timeout (seconds)\n"
" default: depends on cache= option.\n"
" -o writeback|no_writeback enable/disable writeback cache\n"
" default: no_writeback\n"
" -o xattr|no_xattr enable/disable xattr\n"
" default: no_xattr\n"
" --rlimit-nofile=<num> set maximum number of file descriptors\n"
" (0 leaves rlimit unchanged)\n"
" default: min(1000000, fs.file-max - 16384)\n"
" if the current rlimit is lower\n"
);
}
static int fuse_helper_opt_proc(void *data, const char *arg, int key,
struct fuse_args *outargs)
{
(void)data;
(void)outargs;
switch (key) {
case FUSE_OPT_KEY_NONOPT:
fuse_log(FUSE_LOG_ERR, "fuse: invalid argument `%s'\n", arg);
return -1;
default:
/* Pass through unknown options */
return 1;
}
}
static unsigned long get_default_rlimit_nofile(void)
{
g_autofree gchar *file_max_str = NULL;
const rlim_t reserved_fds = 16384; /* leave at least this many fds free */
rlim_t max_fds = 1000000; /* our default RLIMIT_NOFILE target */
rlim_t file_max;
struct rlimit rlim;
/*
* Reduce max_fds below the system-wide maximum, if necessary. This
* ensures there are fds available for other processes so we don't
* cause resource exhaustion.
*/
if (!g_file_get_contents("/proc/sys/fs/file-max", &file_max_str,
NULL, NULL)) {
fuse_log(FUSE_LOG_ERR, "can't read /proc/sys/fs/file-max\n");
exit(1);
}
file_max = g_ascii_strtoull(file_max_str, NULL, 10);
if (file_max < 2 * reserved_fds) {
fuse_log(FUSE_LOG_ERR,
"The fs.file-max sysctl is too low (%lu) to allow a "
"reasonable number of open files.\n",
(unsigned long)file_max);
exit(1);
}
max_fds = MIN(file_max - reserved_fds, max_fds);
if (getrlimit(RLIMIT_NOFILE, &rlim) < 0) {
fuse_log(FUSE_LOG_ERR, "getrlimit(RLIMIT_NOFILE): %m\n");
exit(1);
}
if (rlim.rlim_cur >= max_fds) {
return 0; /* we have more fds available than required! */
}
return max_fds;
}
int fuse_parse_cmdline(struct fuse_args *args, struct fuse_cmdline_opts *opts)
{
memset(opts, 0, sizeof(struct fuse_cmdline_opts));
opts->max_idle_threads = 10;
opts->rlimit_nofile = get_default_rlimit_nofile();
opts->foreground = 1;
if (fuse_opt_parse(args, opts, fuse_helper_opts, fuse_helper_opt_proc) ==
-1) {
return -1;
}
return 0;
}
int fuse_daemonize(int foreground)
{
int ret = 0, rett;
if (!foreground) {
int nullfd;
int waiter[2];
char completed;
if (pipe(waiter)) {
fuse_log(FUSE_LOG_ERR, "fuse_daemonize: pipe: %s\n",
strerror(errno));
return -1;
}
/*
* demonize current process by forking it and killing the
* parent. This makes current process as a child of 'init'.
*/
switch (fork()) {
case -1:
fuse_log(FUSE_LOG_ERR, "fuse_daemonize: fork: %s\n",
strerror(errno));
return -1;
case 0:
break;
default:
_exit(read(waiter[0], &completed,
sizeof(completed) != sizeof(completed)));
}
if (setsid() == -1) {
fuse_log(FUSE_LOG_ERR, "fuse_daemonize: setsid: %s\n",
strerror(errno));
return -1;
}
ret = chdir("/");
nullfd = open("/dev/null", O_RDWR, 0);
if (nullfd != -1) {
rett = dup2(nullfd, 0);
if (!ret) {
ret = rett;
}
rett = dup2(nullfd, 1);
if (!ret) {
ret = rett;
}
rett = dup2(nullfd, 2);
if (!ret) {
ret = rett;
}
if (nullfd > 2) {
close(nullfd);
}
}
/* Propagate completion of daemon initialization */
completed = 1;
rett = write(waiter[1], &completed, sizeof(completed));
if (!ret) {
ret = rett;
}
close(waiter[0]);
close(waiter[1]);
} else {
ret = chdir("/");
}
return ret;
}
void fuse_apply_conn_info_opts(struct fuse_conn_info_opts *opts,
struct fuse_conn_info *conn)
{
if (opts->set_max_write) {
conn->max_write = opts->max_write;
}
if (opts->set_max_background) {
conn->max_background = opts->max_background;
}
if (opts->set_congestion_threshold) {
conn->congestion_threshold = opts->congestion_threshold;
}
if (opts->set_time_gran) {
conn->time_gran = opts->time_gran;
}
if (opts->set_max_readahead) {
conn->max_readahead = opts->max_readahead;
}
#define LL_ENABLE(cond, cap) \
if (cond) \
conn->want |= (cap)
#define LL_DISABLE(cond, cap) \
if (cond) \
conn->want &= ~(cap)
LL_ENABLE(opts->splice_read, FUSE_CAP_SPLICE_READ);
LL_DISABLE(opts->no_splice_read, FUSE_CAP_SPLICE_READ);
LL_ENABLE(opts->splice_write, FUSE_CAP_SPLICE_WRITE);
LL_DISABLE(opts->no_splice_write, FUSE_CAP_SPLICE_WRITE);
LL_ENABLE(opts->splice_move, FUSE_CAP_SPLICE_MOVE);
LL_DISABLE(opts->no_splice_move, FUSE_CAP_SPLICE_MOVE);
LL_ENABLE(opts->auto_inval_data, FUSE_CAP_AUTO_INVAL_DATA);
LL_DISABLE(opts->no_auto_inval_data, FUSE_CAP_AUTO_INVAL_DATA);
LL_DISABLE(opts->no_readdirplus, FUSE_CAP_READDIRPLUS);
LL_DISABLE(opts->no_readdirplus_auto, FUSE_CAP_READDIRPLUS_AUTO);
LL_ENABLE(opts->async_dio, FUSE_CAP_ASYNC_DIO);
LL_DISABLE(opts->no_async_dio, FUSE_CAP_ASYNC_DIO);
LL_ENABLE(opts->writeback_cache, FUSE_CAP_WRITEBACK_CACHE);
LL_DISABLE(opts->no_writeback_cache, FUSE_CAP_WRITEBACK_CACHE);
LL_ENABLE(opts->async_read, FUSE_CAP_ASYNC_READ);
LL_DISABLE(opts->sync_read, FUSE_CAP_ASYNC_READ);
LL_DISABLE(opts->no_remote_posix_lock, FUSE_CAP_POSIX_LOCKS);
LL_DISABLE(opts->no_remote_flock, FUSE_CAP_FLOCK_LOCKS);
}
struct fuse_conn_info_opts *fuse_parse_conn_info_opts(struct fuse_args *args)
{
struct fuse_conn_info_opts *opts;
opts = calloc(1, sizeof(struct fuse_conn_info_opts));
if (opts == NULL) {
fuse_log(FUSE_LOG_ERR, "calloc failed\n");
return NULL;
}
if (fuse_opt_parse(args, opts, conn_info_opt_spec, NULL) == -1) {
free(opts);
return NULL;
}
return opts;
}
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