On Tue, Aug 06, 2024 at 08:38:37PM +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.

Suggested-by: Paul Holzinger Signed-off-by: Stefano Brivio --- conf.c | 1 + passt.c | 2 ++ util.c | 36 ++++++++++++++++++++++++++++++++++++ util.h | 1 + 4 files changed, 40 insertions(+)

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/passt.c b/passt.c index ea5bece..be7e84a 100644 --- a/passt.c +++ b/passt.c @@ -211,6 +211,8 @@ int main(int argc, char **argv)

arch_avx2_exec(argv);

+ close_open_files(argc, argv);

Any reason not to fold this logic into isolate_initial()? Seems like it is part of self-isolation handling. Also, I think this could wait until after the existing isolate_initial() logic. Dropping caps before examining the command line seems like a sensible precaution.

isolate_initial();

c.pasta_netns_fd = c.fd_tap = c.pidfile_fd = -1; diff --git a/util.c b/util.c index 54a9f58..ca627c6 100644 --- a/util.c +++ b/util.c @@ -26,6 +26,7 @@ #include #include #include +#include

#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))

It's weird that close_range() takes unsigneds, although fds are near-universally signed ints.

+ 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 e8bf957..ab11ee7 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