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virtiofsd: cap-ng helpers 

libcap-ng reads /proc during capng_get_caps_process, and virtiofsd's
sandboxing doesn't have /proc mounted; thus we have to do the
caps read before we sandbox it and save/restore the state.

Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
This commit is contained in:
Dr. David Alan Gilbert 2019-12-03 12:23:44 +00:00
parent f779bc5265
commit 2405f3c0d1
2 changed files with 74 additions and 2 deletions
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4
Makefile
View File

@ -327,7 +327,7 @@ HELPERS-y += vhost-user-gpu$(EXESUF)
vhost-user-json-y += contrib/vhost-user-gpu/50-qemu-gpu.json
endif
ifeq ($(CONFIG_LINUX)$(CONFIG_SECCOMP),yy)
ifeq ($(CONFIG_LINUX)$(CONFIG_SECCOMP)$(CONFIG_LIBCAP_NG),yyy)
HELPERS-y += virtiofsd$(EXESUF)
vhost-user-json-y += tools/virtiofsd/50-qemu-virtiofsd.json
endif
@ -675,7 +675,7 @@ rdmacm-mux$(EXESUF): $(rdmacm-mux-obj-y) $(COMMON_LDADDS)
$(call LINK, $^)
# relies on Linux-specific syscalls
ifeq ($(CONFIG_LINUX)$(CONFIG_SECCOMP),yy)
ifeq ($(CONFIG_LINUX)$(CONFIG_SECCOMP)$(CONFIG_LIBCAP_NG),yyy)
virtiofsd$(EXESUF): $(virtiofsd-obj-y) libvhost-user.a $(COMMON_LDADDS)
$(call LINK, $^)
endif

72
tools/virtiofsd/passthrough_ll.c
View File

@ -39,6 +39,7 @@
#include "fuse_virtio.h"
#include "fuse_lowlevel.h"
#include <assert.h>
#include <cap-ng.h>
#include <dirent.h>
#include <errno.h>
#include <inttypes.h>
@ -139,6 +140,13 @@ static const struct fuse_opt lo_opts[] = {
static void unref_inode(struct lo_data *lo, struct lo_inode *inode, uint64_t n);
static struct {
pthread_mutex_t mutex;
void *saved;
} cap;
/* That we loaded cap-ng in the current thread from the saved */
static __thread bool cap_loaded = 0;
static struct lo_inode *lo_find(struct lo_data *lo, struct stat *st);
static int is_dot_or_dotdot(const char *name)
@ -162,6 +170,37 @@ static struct lo_data *lo_data(fuse_req_t req)
return (struct lo_data *)fuse_req_userdata(req);
}
/*
* Load capng's state from our saved state if the current thread
* hadn't previously been loaded.
* returns 0 on success
*/
static int load_capng(void)
{
if (!cap_loaded) {
pthread_mutex_lock(&cap.mutex);
capng_restore_state(&cap.saved);
/*
* restore_state free's the saved copy
* so make another.
*/
cap.saved = capng_save_state();
if (!cap.saved) {
fuse_log(FUSE_LOG_ERR, "capng_save_state (thread)\n");
return -EINVAL;
}
pthread_mutex_unlock(&cap.mutex);
/*
* We want to use the loaded state for our pid,
* not the original
*/
capng_setpid(syscall(SYS_gettid));
cap_loaded = true;
}
return 0;
}
static void lo_map_init(struct lo_map *map)
{
map->elems = NULL;
@ -2023,6 +2062,35 @@ static void setup_namespaces(struct lo_data *lo, struct fuse_session *se)
}
}
/*
* Capture the capability state, we'll need to restore this for individual
* threads later; see load_capng.
*/
static void setup_capng(void)
{
/* Note this accesses /proc so has to happen before the sandbox */
if (capng_get_caps_process()) {
fuse_log(FUSE_LOG_ERR, "capng_get_caps_process\n");
exit(1);
}
pthread_mutex_init(&cap.mutex, NULL);
pthread_mutex_lock(&cap.mutex);
cap.saved = capng_save_state();
if (!cap.saved) {
fuse_log(FUSE_LOG_ERR, "capng_save_state\n");
exit(1);
}
pthread_mutex_unlock(&cap.mutex);
}
static void cleanup_capng(void)
{
free(cap.saved);
cap.saved = NULL;
pthread_mutex_destroy(&cap.mutex);
}
/*
* Make the source directory our root so symlinks cannot escape and no other
* files are accessible. Assumes unshare(CLONE_NEWNS) was already called.
@ -2216,12 +2284,16 @@ int main(int argc, char *argv[])
fuse_daemonize(opts.foreground);
/* Must be before sandbox since it wants /proc */
setup_capng();
setup_sandbox(&lo, se);
/* Block until ctrl+c or fusermount -u */
ret = virtio_loop(se);
fuse_session_unmount(se);
cleanup_capng();
err_out3:
fuse_remove_signal_handlers(se);
err_out2: