public inbox for passt-dev@passt.top
 help / color / mirror / code / Atom feed
* [PATCH v2] passt, util: Close any open file that the parent might have leaked
@ 2024-08-07  8:27 Stefano Brivio
  2024-08-07  8:51 ` David Gibson
  2024-08-07  9:34 ` Paul Holzinger
  0 siblings, 2 replies; 4+ messages in thread
From: Stefano Brivio @ 2024-08-07  8:27 UTC (permalink / raw)
  To: passt-dev; +Cc: Paul Holzinger, David Gibson

If a parent accidentally or due to implementation reasons leaks any
open file, we don't want to have access to them, except for the file
passed via --fd, if any.

This is the case for Podman when Podman's parent leaks files into
Podman: it's not practical for Podman to close unrelated files before
starting pasta, as reported by Paul.

Use close_range(2) to close all open files except for standard streams
and the one from --fd.

Given that parts of conf() depend on other files to be already opened,
such as the epoll file descriptor, we can't easily defer this to a
more convenient point, where --fd was already parsed. Introduce a
minimal, duplicate version of --fd parsing to keep this simple.

Suggested-by: Paul Holzinger <pholzing@redhat.com>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
---
v2: Move call to close_open_files() to isolate_initial()

 conf.c      |  1 +
 isolation.c | 12 +++++++++---
 isolation.h |  2 +-
 passt.c     |  2 +-
 util.c      | 36 ++++++++++++++++++++++++++++++++++++
 util.h      |  1 +
 6 files changed, 49 insertions(+), 5 deletions(-)

diff --git a/conf.c b/conf.c
index 14d8ece..89f5b3d 100644
--- a/conf.c
+++ b/conf.c
@@ -1260,6 +1260,7 @@ void conf(struct ctx *c, int argc, char **argv)
 	c->tcp.fwd_in.mode = c->tcp.fwd_out.mode = FWD_UNSET;
 	c->udp.fwd_in.mode = c->udp.fwd_out.mode = FWD_UNSET;
 
+	optind = 1;
 	do {
 		name = getopt_long(argc, argv, optstring, options, NULL);
 
diff --git a/isolation.c b/isolation.c
index 4956d7e..45fba1e 100644
--- a/isolation.c
+++ b/isolation.c
@@ -29,7 +29,8 @@
  *
  * Executed immediately after startup, drops capabilities we don't
  * need at any point during execution (or which we gain back when we
- * need by joining other namespaces).
+ * need by joining other namespaces), and closes any leaked file we
+ * might have inherited from the parent process.
  *
  * 2. isolate_user()
  * =================
@@ -166,14 +167,17 @@ static void clamp_caps(void)
 }
 
 /**
- * isolate_initial() - Early, config independent self isolation
+ * isolate_initial() - Early, mostly config independent self isolation
+ * @argc:	Argument count
+ * @argv:	Command line options: only --fd (if present) is relevant here
  *
  * Should:
  *  - drop unneeded capabilities
+ *  - close all open files except for standard streams and the one from --fd
  * Musn't:
  *  - remove filesytem access (we need to access files during setup)
  */
-void isolate_initial(void)
+void isolate_initial(int argc, char **argv)
 {
 	uint64_t keep;
 
@@ -207,6 +211,8 @@ void isolate_initial(void)
 		keep |= BIT(CAP_SETFCAP) | BIT(CAP_SYS_PTRACE);
 
 	drop_caps_ep_except(keep);
+
+	close_open_files(argc, argv);
 }
 
 /**
diff --git a/isolation.h b/isolation.h
index 846b2af..80bb68d 100644
--- a/isolation.h
+++ b/isolation.h
@@ -7,7 +7,7 @@
 #ifndef ISOLATION_H
 #define ISOLATION_H
 
-void isolate_initial(void);
+void isolate_initial(int argc, char **argv);
 void isolate_user(uid_t uid, gid_t gid, bool use_userns, const char *userns,
 		  enum passt_modes mode);
 int isolate_prefork(const struct ctx *c);
diff --git a/passt.c b/passt.c
index ea5bece..4b3c306 100644
--- a/passt.c
+++ b/passt.c
@@ -211,7 +211,7 @@ int main(int argc, char **argv)
 
 	arch_avx2_exec(argv);
 
-	isolate_initial();
+	isolate_initial(argc, argv);
 
 	c.pasta_netns_fd = c.fd_tap = c.pidfile_fd = -1;
 
diff --git a/util.c b/util.c
index 07fb21c..bd65b5a 100644
--- a/util.c
+++ b/util.c
@@ -26,6 +26,7 @@
 #include <errno.h>
 #include <stdbool.h>
 #include <linux/errqueue.h>
+#include <getopt.h>
 
 #include "util.h"
 #include "iov.h"
@@ -694,3 +695,38 @@ const char *str_ee_origin(const struct sock_extended_err *ee)
 
 	return "<invalid>";
 }
+
+/**
+ * close_open_files() - Close leaked files, but not --fd, stdin, stdout, stderr
+ * @argc:	Argument count
+ * @argv:	Command line options, as we need to skip any file given via --fd
+ */
+void close_open_files(int argc, char **argv)
+{
+	const struct option optfd[] = { { "fd", required_argument, NULL, 'F' },
+					{ 0 },
+				      };
+	long fd = -1;
+	int name;
+
+	do {
+		name = getopt_long(argc, argv, ":F", optfd, NULL);
+
+		if (name == 'F') {
+			errno = 0;
+			fd = strtol(optarg, NULL, 0);
+
+			if (fd < 0 || errno)
+				die("Invalid --fd: %s", optarg);
+		}
+	} while (name != -1);
+
+	if (fd == -1) {
+		if (close_range(3,	~0U,	CLOSE_RANGE_UNSHARE))
+			die_perror("Failed to close files leaked by parent");
+	} else {
+		if (close_range(3,	fd - 1,	CLOSE_RANGE_UNSHARE) ||
+		    close_range(fd + 1,	~0U,	CLOSE_RANGE_UNSHARE))
+			die_perror("Failed to close files leaked by parent");
+	}
+}
diff --git a/util.h b/util.h
index 83d2b53..cb4d181 100644
--- a/util.h
+++ b/util.h
@@ -183,6 +183,7 @@ int __daemon(int pidfile_fd, int devnull_fd);
 int fls(unsigned long x);
 int write_file(const char *path, const char *buf);
 int write_remainder(int fd, const struct iovec *iov, size_t iovcnt, size_t skip);
+void close_open_files(int argc, char **argv);
 
 /**
  * af_name() - Return name of an address family
-- 
@@ -183,6 +183,7 @@ int __daemon(int pidfile_fd, int devnull_fd);
 int fls(unsigned long x);
 int write_file(const char *path, const char *buf);
 int write_remainder(int fd, const struct iovec *iov, size_t iovcnt, size_t skip);
+void close_open_files(int argc, char **argv);
 
 /**
  * af_name() - Return name of an address family
-- 
2.43.0


^ permalink raw reply related	[flat|nested] 4+ messages in thread

end of thread, other threads:[~2024-08-07 11:11 UTC | newest]

Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2024-08-07  8:27 [PATCH v2] passt, util: Close any open file that the parent might have leaked Stefano Brivio
2024-08-07  8:51 ` David Gibson
2024-08-07  9:34 ` Paul Holzinger
2024-08-07 11:10   ` Stefano Brivio

Code repositories for project(s) associated with this public inbox

	https://passt.top/passt

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for IMAP folder(s).