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 > Signed-off-by: Stefano Brivio Reviewed-by: David Gibson > --- > 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 > #include > #include > +#include > > #include "util.h" > #include "iov.h" > @@ -694,3 +695,43 @@ const char *str_ee_origin(const struct sock_extended_err *ee) > > return ""; > } > + > +/** > + * 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