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virtiofsd: Drop CAP_FSETID if client asked for it

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If client requested killing setuid/setgid bits on file being written, drop
CAP_FSETID capability so that setuid/setgid bits are cleared upon write
automatically.

pjdfstest chown/12.t needs this.

Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
  dgilbert: reworked for libcap-ng
Reviewed-by: Misono Tomohiro <misono.tomohiro@jp.fujitsu.com>
Reviewed-by: Sergio Lopez <slp@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
This commit is contained in:
Vivek Goyal 2019-08-13 15:29:44 -04:00 committed by Dr. David Alan Gilbert
parent 2405f3c0d1
commit ee88465224
1 changed files with 105 additions and 0 deletions
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105
tools/virtiofsd/passthrough_ll.c
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@ -201,6 +201,91 @@ static int load_capng(void)
return 0;
}
/*
* Helpers for dropping and regaining effective capabilities. Returns 0
* on success, error otherwise
*/
static int drop_effective_cap(const char *cap_name, bool *cap_dropped)
{
int cap, ret;
cap = capng_name_to_capability(cap_name);
if (cap < 0) {
ret = errno;
fuse_log(FUSE_LOG_ERR, "capng_name_to_capability(%s) failed:%s\n",
cap_name, strerror(errno));
goto out;
}
if (load_capng()) {
ret = errno;
fuse_log(FUSE_LOG_ERR, "load_capng() failed\n");
goto out;
}
/* We dont have this capability in effective set already. */
if (!capng_have_capability(CAPNG_EFFECTIVE, cap)) {
ret = 0;
goto out;
}
if (capng_update(CAPNG_DROP, CAPNG_EFFECTIVE, cap)) {
ret = errno;
fuse_log(FUSE_LOG_ERR, "capng_update(DROP,) failed\n");
goto out;
}
if (capng_apply(CAPNG_SELECT_CAPS)) {
ret = errno;
fuse_log(FUSE_LOG_ERR, "drop:capng_apply() failed\n");
goto out;
}
ret = 0;
if (cap_dropped) {
*cap_dropped = true;
}
out:
return ret;
}
static int gain_effective_cap(const char *cap_name)
{
int cap;
int ret = 0;
cap = capng_name_to_capability(cap_name);
if (cap < 0) {
ret = errno;
fuse_log(FUSE_LOG_ERR, "capng_name_to_capability(%s) failed:%s\n",
cap_name, strerror(errno));
goto out;
}
if (load_capng()) {
ret = errno;
fuse_log(FUSE_LOG_ERR, "load_capng() failed\n");
goto out;
}
if (capng_update(CAPNG_ADD, CAPNG_EFFECTIVE, cap)) {
ret = errno;
fuse_log(FUSE_LOG_ERR, "capng_update(ADD,) failed\n");
goto out;
}
if (capng_apply(CAPNG_SELECT_CAPS)) {
ret = errno;
fuse_log(FUSE_LOG_ERR, "gain:capng_apply() failed\n");
goto out;
}
ret = 0;
out:
return ret;
}
static void lo_map_init(struct lo_map *map)
{
map->elems = NULL;
@ -1577,6 +1662,7 @@ static void lo_write_buf(fuse_req_t req, fuse_ino_t ino,
(void)ino;
ssize_t res;
struct fuse_bufvec out_buf = FUSE_BUFVEC_INIT(fuse_buf_size(in_buf));
bool cap_fsetid_dropped = false;
out_buf.buf[0].flags = FUSE_BUF_IS_FD | FUSE_BUF_FD_SEEK;
out_buf.buf[0].fd = lo_fi_fd(req, fi);
@ -1588,12 +1674,31 @@ static void lo_write_buf(fuse_req_t req, fuse_ino_t ino,
out_buf.buf[0].size, (unsigned long)off);
}
/*
* If kill_priv is set, drop CAP_FSETID which should lead to kernel
* clearing setuid/setgid on file.
*/
if (fi->kill_priv) {
res = drop_effective_cap("FSETID", &cap_fsetid_dropped);
if (res != 0) {
fuse_reply_err(req, res);
return;
}
}
res = fuse_buf_copy(&out_buf, in_buf);
if (res < 0) {
fuse_reply_err(req, -res);
} else {
fuse_reply_write(req, (size_t)res);
}
if (cap_fsetid_dropped) {
res = gain_effective_cap("FSETID");
if (res) {
fuse_log(FUSE_LOG_ERR, "Failed to gain CAP_FSETID\n");
}
}
}
static void lo_statfs(fuse_req_t req, fuse_ino_t ino)