[PATCH v7] passt, util: Close any open file that the parent might have leaked

[PATCH v7] passt, util: Close any open file that the parent might have leaked

[Stefano Brivio]

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.

As we need to check that the passed --fd option doesn't exceed
INT_MAX, because we'll parse it with strtol() but file descriptor
indices are signed ints (regardless of the arguments close_range()
take), extend the existing check in the actual --fd parsing in conf(),
also rejecting file descriptors numbers that match standard streams,
while at it.

Suggested-by: Paul Holzinger <pholzing@redhat.com>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
---
v7: (yes, seriously) don't close STDERR_FILENO in the general case,
    start from STDERR_FILENO + 1

v6: (seriously?) fix STDERR_FILENO comparison in conf()

v5: Reject any --fd matching standard streams

v4: c->fd_tap, as used in conf(), is an int: don't assign to it
    directly from strtol(), or we won't catch overflows

v3: Handle --fd 3 case, and don't overflow if the --fd number exceeds
    UINT_MAX: add an explicit check to ensure it's less than INT_MAX

v2: Move call to close_open_files() to isolate_initial()

 conf.c      |  8 ++++++--
 isolation.c | 12 +++++++++---
 isolation.h |  2 +-
 passt.c     |  2 +-
 util.c      | 41 +++++++++++++++++++++++++++++++++++++++++
 util.h      |  1 +
 6 files changed, 59 insertions(+), 7 deletions(-)

diff --git a/conf.c b/conf.c
index 14d8ece..2f5d649 100644
--- a/conf.c
+++ b/conf.c
@@ -1245,6 +1245,7 @@ void conf(struct ctx *c, int argc, char **argv)
 	const char *optstring;
 	size_t logsize = 0;
 	char *runas = NULL;
+	long fd_tap_opt;
 	int name, ret;
 	uid_t uid;
 	gid_t gid;
@@ -1260,6 +1261,7 @@ 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);
 
@@ -1424,11 +1426,13 @@ void conf(struct ctx *c, int argc, char **argv)
 			break;
 		case 'F':
 			errno = 0;
-			c->fd_tap = strtol(optarg, NULL, 0);
+			fd_tap_opt = strtol(optarg, NULL, 0);
 
-			if (c->fd_tap < 0 || errno)
+			if (errno ||
+			    fd_tap_opt <= STDERR_FILENO || fd_tap_opt > INT_MAX)
 				die("Invalid --fd: %s", optarg);
 
+			c->fd_tap = fd_tap_opt;
 			c->one_off = true;
 			*c->sock_path = 0;
 			break;
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..7761bd3 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 +695,43 @@ 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, rc;
+
+	do {
+		name = getopt_long(argc, argv, ":F", optfd, NULL);
+
+		if (name == 'F') {
+			errno = 0;
+			fd = strtol(optarg, NULL, 0);
+
+			if (errno || fd <= STDERR_FILENO || fd > INT_MAX)
+				die("Invalid --fd: %s", optarg);
+		}
+	} while (name != -1);
+
+	if (fd == -1) {
+		rc = close_range(STDERR_FILENO + 1, ~0U, CLOSE_RANGE_UNSHARE);
+	} else if (fd == STDERR_FILENO + 1) { /* Still a single range */
+		rc = close_range(STDERR_FILENO + 2, ~0U, CLOSE_RANGE_UNSHARE);
+	} else {
+		rc = close_range(STDERR_FILENO + 1, fd - 1,
+				 CLOSE_RANGE_UNSHARE);
+		if (!rc)
+			rc = close_range(fd + 1, ~0U, CLOSE_RANGE_UNSHARE);
+	}
+
+	if (rc)
+		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

Re: [PATCH v7] passt, util: Close any open file that the parent might have leaked

[David Gibson]

[-- Attachment #1: Type: text/plain, Size: 7651 bytes --]

On Thu, Aug 08, 2024 at 05:42:49AM +0200, Stefano Brivio wrote:
> 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.
> 
> As we need to check that the passed --fd option doesn't exceed
> INT_MAX, because we'll parse it with strtol() but file descriptor
> indices are signed ints (regardless of the arguments close_range()
> take), extend the existing check in the actual --fd parsing in conf(),
> also rejecting file descriptors numbers that match standard streams,
> while at it.
> 
> Suggested-by: Paul Holzinger <pholzing@redhat.com>
> Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

Reviewed-by: David Gibson <david@gibson.dropbear.id.au>

> ---
> v7: (yes, seriously) don't close STDERR_FILENO in the general case,
>     start from STDERR_FILENO + 1
> 
> v6: (seriously?) fix STDERR_FILENO comparison in conf()
> 
> v5: Reject any --fd matching standard streams
> 
> v4: c->fd_tap, as used in conf(), is an int: don't assign to it
>     directly from strtol(), or we won't catch overflows
> 
> v3: Handle --fd 3 case, and don't overflow if the --fd number exceeds
>     UINT_MAX: add an explicit check to ensure it's less than INT_MAX
> 
> v2: Move call to close_open_files() to isolate_initial()
> 
>  conf.c      |  8 ++++++--
>  isolation.c | 12 +++++++++---
>  isolation.h |  2 +-
>  passt.c     |  2 +-
>  util.c      | 41 +++++++++++++++++++++++++++++++++++++++++
>  util.h      |  1 +
>  6 files changed, 59 insertions(+), 7 deletions(-)
> 
> diff --git a/conf.c b/conf.c
> index 14d8ece..2f5d649 100644
> --- a/conf.c
> +++ b/conf.c
> @@ -1245,6 +1245,7 @@ void conf(struct ctx *c, int argc, char **argv)
>  	const char *optstring;
>  	size_t logsize = 0;
>  	char *runas = NULL;
> +	long fd_tap_opt;
>  	int name, ret;
>  	uid_t uid;
>  	gid_t gid;
> @@ -1260,6 +1261,7 @@ 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);
>  
> @@ -1424,11 +1426,13 @@ void conf(struct ctx *c, int argc, char **argv)
>  			break;
>  		case 'F':
>  			errno = 0;
> -			c->fd_tap = strtol(optarg, NULL, 0);
> +			fd_tap_opt = strtol(optarg, NULL, 0);
>  
> -			if (c->fd_tap < 0 || errno)
> +			if (errno ||
> +			    fd_tap_opt <= STDERR_FILENO || fd_tap_opt > INT_MAX)
>  				die("Invalid --fd: %s", optarg);
>  
> +			c->fd_tap = fd_tap_opt;
>  			c->one_off = true;
>  			*c->sock_path = 0;
>  			break;
> 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..7761bd3 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 +695,43 @@ 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, rc;
> +
> +	do {
> +		name = getopt_long(argc, argv, ":F", optfd, NULL);
> +
> +		if (name == 'F') {
> +			errno = 0;
> +			fd = strtol(optarg, NULL, 0);
> +
> +			if (errno || fd <= STDERR_FILENO || fd > INT_MAX)
> +				die("Invalid --fd: %s", optarg);
> +		}
> +	} while (name != -1);
> +
> +	if (fd == -1) {
> +		rc = close_range(STDERR_FILENO + 1, ~0U, CLOSE_RANGE_UNSHARE);
> +	} else if (fd == STDERR_FILENO + 1) { /* Still a single range */
> +		rc = close_range(STDERR_FILENO + 2, ~0U, CLOSE_RANGE_UNSHARE);
> +	} else {
> +		rc = close_range(STDERR_FILENO + 1, fd - 1,
> +				 CLOSE_RANGE_UNSHARE);
> +		if (!rc)
> +			rc = close_range(fd + 1, ~0U, CLOSE_RANGE_UNSHARE);
> +	}
> +
> +	if (rc)
> +		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

-- 
David Gibson (he or they)	| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you, not the other way
				| around.
http://www.ozlabs.org/~dgibson

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Re: [PATCH v7] passt, util: Close any open file that the parent might have leaked

[Paul Holzinger]

On 08/08/2024 05:42, Stefano Brivio wrote:
> 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.
>
> As we need to check that the passed --fd option doesn't exceed
> INT_MAX, because we'll parse it with strtol() but file descriptor
> indices are signed ints (regardless of the arguments close_range()
> take), extend the existing check in the actual --fd parsing in conf(),
> also rejecting file descriptors numbers that match standard streams,
> while at it.
>
> Suggested-by: Paul Holzinger <pholzing@redhat.com>
> Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
Reviewed-by: Paul Holzinger <pholzing@redhat.com>
> ---
> v7: (yes, seriously) don't close STDERR_FILENO in the general case,
>      start from STDERR_FILENO + 1
>
> v6: (seriously?) fix STDERR_FILENO comparison in conf()
>
> v5: Reject any --fd matching standard streams
>
> v4: c->fd_tap, as used in conf(), is an int: don't assign to it
>      directly from strtol(), or we won't catch overflows
>
> v3: Handle --fd 3 case, and don't overflow if the --fd number exceeds
>      UINT_MAX: add an explicit check to ensure it's less than INT_MAX
>
> v2: Move call to close_open_files() to isolate_initial()
>
>   conf.c      |  8 ++++++--
>   isolation.c | 12 +++++++++---
>   isolation.h |  2 +-
>   passt.c     |  2 +-
>   util.c      | 41 +++++++++++++++++++++++++++++++++++++++++
>   util.h      |  1 +
>   6 files changed, 59 insertions(+), 7 deletions(-)

-- 
Paul Holzinger