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Thu, 16 Jan 2020 15:21:38 +0000 (UTC) References: <20191212163904.159893-1-dgilbert@redhat.com> <20191212163904.159893-54-dgilbert@redhat.com> User-agent: mu4e 1.2.0; emacs 26.3 From: Sergio Lopez To: qemu-devel@nongnu.org Subject: Re: [PATCH 053/104] virtiofsd: Drop CAP_FSETID if client asked for it Message-ID: <87muanwhom.fsf@redhat.com> In-reply-to: <20191212163904.159893-54-dgilbert@redhat.com> Date: Thu, 16 Jan 2020 16:21:35 +0100 MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: multipart/signed; boundary="=-=-="; micalg=pgp-sha256; protocol="application/pgp-signature" X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 205.139.110.61 X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: "Dr. David Alan Gilbert \(git\)" , stefanha@redhat.com, vgoyal@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" --=-=-= Content-Type: text/plain Dr. David Alan Gilbert (git) writes: > From: Vivek Goyal > > 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 > dgilbert: reworked for libcap-ng > --- > tools/virtiofsd/passthrough_ll.c | 105 +++++++++++++++++++++++++++++++ > 1 file changed, 105 insertions(+) > > diff --git a/tools/virtiofsd/passthrough_ll.c b/tools/virtiofsd/passthrough_ll.c > index 6a09b28608..ab318a6f36 100644 > --- a/tools/virtiofsd/passthrough_ll.c > +++ b/tools/virtiofsd/passthrough_ll.c > @@ -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; > @@ -1559,6 +1644,7 @@ 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); > @@ -1570,12 +1656,31 @@ 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, 0); > 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) Fiddling with the capabilities for clearing setuid/setgid on a file seems a bit weird to me, but I see this was already discussed in https://lkml.org/lkml/2019/5/20/1229, so... 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