* [PATCH v2] feat: Add cli option '--pass-fds' for pasta mode. @ 2026-07-18 16:14 Richard Lawrence 2026-07-18 16:52 ` Lawrence, Richard E 0 siblings, 1 reply; 3+ messages in thread From: Richard Lawrence @ 2026-07-18 16:14 UTC (permalink / raw) To: passt-dev; +Cc: jbash, Richard Lawrence, Richard Lawrence From: Richard Lawrence <rarensu@tamu.edu> When pasta mode is used to launch an executable (`pasta [COMMAND]`) and that executable accepts inputs in the form of arbitrary file descriptors (such as `bwrap`), then passt should not stand in the way of the parent process handing off those file descriptors to the child process. See bug 204 for additional discussion. The `pass-fds` option accepts a comma-separated list of file descriptor numbers. `conf_pass_fds()` parses the command line argument, then `isolate_fds()` skips closing the specified fds by calling `close_range()` on the gaps between them. Additionally, the tap fd is safely relocated to the lowest unused fd number which it at least 3, to avoid accidentally overwriting an existing fd. Signed-off-by: Richard Lawrence <rlawrence@tamu.edu> --- conf.c | 66 ++++++++++++++++++++++++++++++++++++++++++++++++++- conf.h | 1 + isolation.c | 68 ++++++++++++++++++++++++++++++++++++++++++----------- passt.1 | 5 ++++ 4 files changed, 125 insertions(+), 15 deletions(-) diff --git a/conf.c b/conf.c index 0fcba5c..3246735 100644 --- a/conf.c +++ b/conf.c @@ -732,7 +732,9 @@ pasta_opts: " Don't copy all addresses to namespace\n" " --ns-mac-addr ADDR Set MAC address on tap interface\n" " --no-splice Disable inbound socket splicing\n" - " --splice-only Only enable loopback forwarding\n"); + " --splice-only Only enable loopback forwarding\n" + " --pass-fds FDS Comma-separated list of fds to pass to\n" + " the spawned command\n"); passt_exit(status); } @@ -1183,6 +1185,63 @@ int conf_tap_fd(int argc, char **argv) return val; } +/** + * conf_pass_fds() - Read fds as supplied by --pass-fds command line option + * @argc: Argument count + * @argv: Command line options + * @fds: Array where we store the parsed fds + * @max_fds: Maximum size of the array + * + * Return: number of parsed fds, or -1 if option not specified + */ +int conf_pass_fds(int argc, char **argv, int *fds, int max_fds) +{ + const struct option opt[] = { { "pass-fds", required_argument, NULL, 33 }, + { 0 }, }; + const char *fdsarg = NULL; + int name, fds_cnt = 0; + int old_opterr; + + old_opterr = opterr; + opterr = 0; + optind = 0; + do { + name = getopt_long(argc, argv, "-:", opt, NULL); + if (name == 33) + fdsarg = optarg; + } while (name != -1); + opterr = old_opterr; + + if (!fdsarg) + return -1; + + while (*fdsarg) { + unsigned long val; + char *endptr; + + val = strtoul(fdsarg, &endptr, 10); + if (fdsarg == endptr) + die("Invalid --pass-fds option: %s", fdsarg); + + if (val > INT_MAX) + die("Invalid file descriptor in --pass-fds: %lu", val); + + if (fds_cnt >= max_fds) + die("Too many file descriptors in --pass-fds"); + + fds[fds_cnt++] = (int)val; + + if (*endptr == ',') + fdsarg = endptr + 1; + else if (*endptr == '\0') + fdsarg = endptr; + else + die("Invalid character in --pass-fds option: %s", fdsarg); + } + + return fds_cnt; +} + /** * conf_addr() - Configure guest address with -a option * @c: Execution context @@ -1331,6 +1390,7 @@ void conf(struct ctx *c, int argc, char **argv) {"stats", required_argument, NULL, 31 }, {"conf-path", required_argument, NULL, 'c' }, {"chroot-fallback", no_argument, NULL, 32 }, + {"pass-fds", required_argument, NULL, 33 }, { 0 }, }; const char *optstring = "+dqfel:hs:c:F:I:p:P:m:a:n:M:g:i:o:D:S:H:461t:u:T:U:"; @@ -1572,6 +1632,10 @@ void conf(struct ctx *c, int argc, char **argv) case 32: c->chroot_fallback = true; break; + case 33: + if (c->mode != MODE_PASTA) + die("--pass-fds is for pasta mode only"); + break; case 'd': c->debug = 1; c->quiet = 0; diff --git a/conf.h b/conf.h index 19bf9bc..3489f35 100644 --- a/conf.h +++ b/conf.h @@ -7,6 +7,7 @@ #define CONF_H enum passt_modes conf_mode(int argc, char *argv[]); +int conf_pass_fds(int argc, char **argv, int *fds, int max_fds); int conf_tap_fd(int argc, char **argv); void conf(struct ctx *c, int argc, char **argv); void conf_listen_handler(struct ctx *c, uint32_t events); diff --git a/isolation.c b/isolation.c index 94cbe7f..0632f7f 100644 --- a/isolation.c +++ b/isolation.c @@ -249,32 +249,72 @@ void isolate_initial(void) } /* - * isolate_fds() - Close leaked files, but not --fd, stdin, stdout, stderr + * isolate_fds() - Close leaked files, but not --fd, --pass-fds, standard streams * @argc: Argument count - * @argv: Command line options, as we need to skip any file given via --fd + * @argv: Command line options * * Should: - * - close all open files except for standard streams and the one from --fd + * - close all open files except for standard streams, --fd, and --pass-fds * - move the --fd descriptor out of the range 0-2 * * Return: new fd number for descriptor from --fd, or -1 if not specified */ int isolate_fds(int argc, char **argv) { - int fd, close_from = STDERR_FILENO + 1; + int prev_fd = STDERR_FILENO; // Keep standard streams + int fds[1024 + 1]; + int fds_cnt = 0; + int tap_fd; + int rc = 0; + + tap_fd = conf_tap_fd(argc, argv); + if (tap_fd >= 0 && tap_fd < 3) { + /* Move the passed fd to a more convenient location */ + int new_fd = fcntl(tap_fd, F_DUPFD, 3); + + if (new_fd < 0) + die_perror("Could not relocate --fd descriptor"); - fd = conf_tap_fd(argc, argv); + close(tap_fd); + tap_fd = new_fd; + } - if (fd >= 0) { - /* Move the passed fd to a more convenient location */ - if (fd != close_from && - (dup2(fd, close_from) != close_from || - close(fd))) - die_perror("Could not move --fd descriptor"); - fd = close_from++; + if (tap_fd >= 0) + /* Keep the tap fd */ + fds[fds_cnt++] = tap_fd; + + rc = conf_pass_fds(argc, argv, fds + fds_cnt, 1024); + if (rc > 0) + /* Keep the pass-fds */ + fds_cnt += rc; + + rc = 0; + + while (1) { + int min_fd = -1; + + /* Find the next-lowest fd to keep */ + for (int i = 0; i < fds_cnt; i++) { + if (fds[i] > prev_fd && (min_fd == -1 || fds[i] < min_fd)) + min_fd = fds[i]; + } + + if (min_fd == -1) + break; + + if (min_fd > prev_fd + 1) { + /* Close fds between two kept fds */ + if (close_range(prev_fd + 1, min_fd - 1, CLOSE_RANGE_UNSHARE)) + rc = -1; + } + prev_fd = min_fd; } + + /* Close all other fds */ + if (close_range(prev_fd + 1, ~0U, CLOSE_RANGE_UNSHARE)) + rc = -1; - if (close_range(close_from, ~0U, CLOSE_RANGE_UNSHARE)) { + if (rc) { if (errno == ENOSYS || errno == EINVAL) { /* This probably means close_range() or the * CLOSE_RANGE_UNSHARE flag is not supported by the @@ -288,7 +328,7 @@ int isolate_fds(int argc, char **argv) } } - return fd; + return tap_fd; } /** diff --git a/passt.1 b/passt.1 index 995590a..bcd3aff 100644 --- a/passt.1 +++ b/passt.1 @@ -755,6 +755,11 @@ of local traffic in pasta\fR in the \fBNOTES\fR for more details. Do not create a tap device in the namespace. In this mode, \fIpasta\fR only forwards loopback traffic between namespaces. +.TP +.BR \-\-pass\-fds " " \fIfds\fR +Pass a comma-separated list of file descriptors to the spawned command. +These file descriptors will be kept open. + .SH EXAMPLES .SS \fBpasta -- 2.52.0 ^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH v2] feat: Add cli option '--pass-fds' for pasta mode. 2026-07-18 16:14 [PATCH v2] feat: Add cli option '--pass-fds' for pasta mode Richard Lawrence @ 2026-07-18 16:52 ` Lawrence, Richard E 2026-07-19 19:14 ` Lawrence, Richard E 0 siblings, 1 reply; 3+ messages in thread From: Lawrence, Richard E @ 2026-07-18 16:52 UTC (permalink / raw) To: passt-dev; +Cc: jbash [-- Attachment #1: Type: text/plain, Size: 10002 bytes --] Nitpicks: * we use STDERR_FILENO to represent 2, so the target of fcntl should be STDERR_FILENO + 1 rather than literal 3. * I think it would be clearer if prev_fd was declared but not initially defined, and then set to STDERR_FILENO just before the loop, so that a comment like /* keep standard streams */ would not be among a bunch of variable declarations, but would be located near where the variable is first used. * I think it would be clearer if min_fd was named next_fd by analogy to prev_fd. ________________________________ From: Richard Lawrence <rlawrence@tamu.edu> Sent: Saturday, July 18, 2026 11:14 AM To: passt-dev@passt.top <passt-dev@passt.top> Cc: jbash@jbash.com <jbash@jbash.com>; Lawrence, Richard E <rlawrence@tamu.edu>; Lawrence, Richard E <rlawrence@tamu.edu> Subject: [PATCH v2] feat: Add cli option '--pass-fds' for pasta mode. From: Richard Lawrence <rarensu@tamu.edu> When pasta mode is used to launch an executable (`pasta [COMMAND]`) and that executable accepts inputs in the form of arbitrary file descriptors (such as `bwrap`), then passt should not stand in the way of the parent process handing off those file descriptors to the child process. See bug 204 for additional discussion. The `pass-fds` option accepts a comma-separated list of file descriptor numbers. `conf_pass_fds()` parses the command line argument, then `isolate_fds()` skips closing the specified fds by calling `close_range()` on the gaps between them. Additionally, the tap fd is safely relocated to the lowest unused fd number which it at least 3, to avoid accidentally overwriting an existing fd. Signed-off-by: Richard Lawrence <rlawrence@tamu.edu> --- conf.c | 66 ++++++++++++++++++++++++++++++++++++++++++++++++++- conf.h | 1 + isolation.c | 68 ++++++++++++++++++++++++++++++++++++++++++----------- passt.1 | 5 ++++ 4 files changed, 125 insertions(+), 15 deletions(-) diff --git a/conf.c b/conf.c index 0fcba5c..3246735 100644 --- a/conf.c +++ b/conf.c @@ -732,7 +732,9 @@ pasta_opts: " Don't copy all addresses to namespace\n" " --ns-mac-addr ADDR Set MAC address on tap interface\n" " --no-splice Disable inbound socket splicing\n" - " --splice-only Only enable loopback forwarding\n"); + " --splice-only Only enable loopback forwarding\n" + " --pass-fds FDS Comma-separated list of fds to pass to\n" + " the spawned command\n"); passt_exit(status); } @@ -1183,6 +1185,63 @@ int conf_tap_fd(int argc, char **argv) return val; } +/** + * conf_pass_fds() - Read fds as supplied by --pass-fds command line option + * @argc: Argument count + * @argv: Command line options + * @fds: Array where we store the parsed fds + * @max_fds: Maximum size of the array + * + * Return: number of parsed fds, or -1 if option not specified + */ +int conf_pass_fds(int argc, char **argv, int *fds, int max_fds) +{ + const struct option opt[] = { { "pass-fds", required_argument, NULL, 33 }, + { 0 }, }; + const char *fdsarg = NULL; + int name, fds_cnt = 0; + int old_opterr; + + old_opterr = opterr; + opterr = 0; + optind = 0; + do { + name = getopt_long(argc, argv, "-:", opt, NULL); + if (name == 33) + fdsarg = optarg; + } while (name != -1); + opterr = old_opterr; + + if (!fdsarg) + return -1; + + while (*fdsarg) { + unsigned long val; + char *endptr; + + val = strtoul(fdsarg, &endptr, 10); + if (fdsarg == endptr) + die("Invalid --pass-fds option: %s", fdsarg); + + if (val > INT_MAX) + die("Invalid file descriptor in --pass-fds: %lu", val); + + if (fds_cnt >= max_fds) + die("Too many file descriptors in --pass-fds"); + + fds[fds_cnt++] = (int)val; + + if (*endptr == ',') + fdsarg = endptr + 1; + else if (*endptr == '\0') + fdsarg = endptr; + else + die("Invalid character in --pass-fds option: %s", fdsarg); + } + + return fds_cnt; +} + /** * conf_addr() - Configure guest address with -a option * @c: Execution context @@ -1331,6 +1390,7 @@ void conf(struct ctx *c, int argc, char **argv) {"stats", required_argument, NULL, 31 }, {"conf-path", required_argument, NULL, 'c' }, {"chroot-fallback", no_argument, NULL, 32 }, + {"pass-fds", required_argument, NULL, 33 }, { 0 }, }; const char *optstring = "+dqfel:hs:c:F:I:p:P:m:a:n:M:g:i:o:D:S:H:461t:u:T:U:"; @@ -1572,6 +1632,10 @@ void conf(struct ctx *c, int argc, char **argv) case 32: c->chroot_fallback = true; break; + case 33: + if (c->mode != MODE_PASTA) + die("--pass-fds is for pasta mode only"); + break; case 'd': c->debug = 1; c->quiet = 0; diff --git a/conf.h b/conf.h index 19bf9bc..3489f35 100644 --- a/conf.h +++ b/conf.h @@ -7,6 +7,7 @@ #define CONF_H enum passt_modes conf_mode(int argc, char *argv[]); +int conf_pass_fds(int argc, char **argv, int *fds, int max_fds); int conf_tap_fd(int argc, char **argv); void conf(struct ctx *c, int argc, char **argv); void conf_listen_handler(struct ctx *c, uint32_t events); diff --git a/isolation.c b/isolation.c index 94cbe7f..0632f7f 100644 --- a/isolation.c +++ b/isolation.c @@ -249,32 +249,72 @@ void isolate_initial(void) } /* - * isolate_fds() - Close leaked files, but not --fd, stdin, stdout, stderr + * isolate_fds() - Close leaked files, but not --fd, --pass-fds, standard streams * @argc: Argument count - * @argv: Command line options, as we need to skip any file given via --fd + * @argv: Command line options * * Should: - * - close all open files except for standard streams and the one from --fd + * - close all open files except for standard streams, --fd, and --pass-fds * - move the --fd descriptor out of the range 0-2 * * Return: new fd number for descriptor from --fd, or -1 if not specified */ int isolate_fds(int argc, char **argv) { - int fd, close_from = STDERR_FILENO + 1; + int prev_fd = STDERR_FILENO; // Keep standard streams + int fds[1024 + 1]; + int fds_cnt = 0; + int tap_fd; + int rc = 0; + + tap_fd = conf_tap_fd(argc, argv); + if (tap_fd >= 0 && tap_fd < 3) { + /* Move the passed fd to a more convenient location */ + int new_fd = fcntl(tap_fd, F_DUPFD, 3); + + if (new_fd < 0) + die_perror("Could not relocate --fd descriptor"); - fd = conf_tap_fd(argc, argv); + close(tap_fd); + tap_fd = new_fd; + } - if (fd >= 0) { - /* Move the passed fd to a more convenient location */ - if (fd != close_from && - (dup2(fd, close_from) != close_from || - close(fd))) - die_perror("Could not move --fd descriptor"); - fd = close_from++; + if (tap_fd >= 0) + /* Keep the tap fd */ + fds[fds_cnt++] = tap_fd; + + rc = conf_pass_fds(argc, argv, fds + fds_cnt, 1024); + if (rc > 0) + /* Keep the pass-fds */ + fds_cnt += rc; + + rc = 0; + + while (1) { + int min_fd = -1; + + /* Find the next-lowest fd to keep */ + for (int i = 0; i < fds_cnt; i++) { + if (fds[i] > prev_fd && (min_fd == -1 || fds[i] < min_fd)) + min_fd = fds[i]; + } + + if (min_fd == -1) + break; + + if (min_fd > prev_fd + 1) { + /* Close fds between two kept fds */ + if (close_range(prev_fd + 1, min_fd - 1, CLOSE_RANGE_UNSHARE)) + rc = -1; + } + prev_fd = min_fd; } + + /* Close all other fds */ + if (close_range(prev_fd + 1, ~0U, CLOSE_RANGE_UNSHARE)) + rc = -1; - if (close_range(close_from, ~0U, CLOSE_RANGE_UNSHARE)) { + if (rc) { if (errno == ENOSYS || errno == EINVAL) { /* This probably means close_range() or the * CLOSE_RANGE_UNSHARE flag is not supported by the @@ -288,7 +328,7 @@ int isolate_fds(int argc, char **argv) } } - return fd; + return tap_fd; } /** diff --git a/passt.1 b/passt.1 index 995590a..bcd3aff 100644 --- a/passt.1 +++ b/passt.1 @@ -755,6 +755,11 @@ of local traffic in pasta\fR in the \fBNOTES\fR for more details. Do not create a tap device in the namespace. In this mode, \fIpasta\fR only forwards loopback traffic between namespaces. +.TP +.BR \-\-pass\-fds " " \fIfds\fR +Pass a comma-separated list of file descriptors to the spawned command. +These file descriptors will be kept open. + .SH EXAMPLES .SS \fBpasta -- 2.52.0 [-- Attachment #2: Type: text/html, Size: 22932 bytes --] ^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH v2] feat: Add cli option '--pass-fds' for pasta mode. 2026-07-18 16:52 ` Lawrence, Richard E @ 2026-07-19 19:14 ` Lawrence, Richard E 0 siblings, 0 replies; 3+ messages in thread From: Lawrence, Richard E @ 2026-07-19 19:14 UTC (permalink / raw) To: passt-dev; +Cc: jbash [-- Attachment #1: Type: text/plain, Size: 10906 bytes --] Nitpicks: * Literal 1024 used as the max pass-fds is magic. It should either be dynamic, or defined as a preprocessor directive. * It is at least computationally awkward and possibly even unsafe to parse fd and pass-fds independently from the rest of the args. If the arg structure is ever extended to support an unordered mix of keyword and positional arguments, then these independent implementations become a maintenance burden. * In conf_pass_fds(), the die statement only includes the particular substring that triggered the failure, which could result in a misleading or unhelpful error message. ________________________________ From: Lawrence, Richard E <rlawrence@tamu.edu> Sent: Saturday, July 18, 2026 11:52 AM To: passt-dev@passt.top <passt-dev@passt.top> Cc: jbash@jbash.com <jbash@jbash.com> Subject: Re: [PATCH v2] feat: Add cli option '--pass-fds' for pasta mode. Nitpicks: * we use STDERR_FILENO to represent 2, so the target of fcntl should be STDERR_FILENO + 1 rather than literal 3. * I think it would be clearer if prev_fd was declared but not initially defined, and then set to STDERR_FILENO just before the loop, so that a comment like /* keep standard streams */ would not be among a bunch of variable declarations, but would be located near where the variable is first used. * I think it would be clearer if min_fd was named next_fd by analogy to prev_fd. ________________________________ From: Richard Lawrence <rlawrence@tamu.edu> Sent: Saturday, July 18, 2026 11:14 AM To: passt-dev@passt.top <passt-dev@passt.top> Cc: jbash@jbash.com <jbash@jbash.com>; Lawrence, Richard E <rlawrence@tamu.edu>; Lawrence, Richard E <rlawrence@tamu.edu> Subject: [PATCH v2] feat: Add cli option '--pass-fds' for pasta mode. From: Richard Lawrence <rarensu@tamu.edu> When pasta mode is used to launch an executable (`pasta [COMMAND]`) and that executable accepts inputs in the form of arbitrary file descriptors (such as `bwrap`), then passt should not stand in the way of the parent process handing off those file descriptors to the child process. See bug 204 for additional discussion. The `pass-fds` option accepts a comma-separated list of file descriptor numbers. `conf_pass_fds()` parses the command line argument, then `isolate_fds()` skips closing the specified fds by calling `close_range()` on the gaps between them. Additionally, the tap fd is safely relocated to the lowest unused fd number which it at least 3, to avoid accidentally overwriting an existing fd. Signed-off-by: Richard Lawrence <rlawrence@tamu.edu> --- conf.c | 66 ++++++++++++++++++++++++++++++++++++++++++++++++++- conf.h | 1 + isolation.c | 68 ++++++++++++++++++++++++++++++++++++++++++----------- passt.1 | 5 ++++ 4 files changed, 125 insertions(+), 15 deletions(-) diff --git a/conf.c b/conf.c index 0fcba5c..3246735 100644 --- a/conf.c +++ b/conf.c @@ -732,7 +732,9 @@ pasta_opts: " Don't copy all addresses to namespace\n" " --ns-mac-addr ADDR Set MAC address on tap interface\n" " --no-splice Disable inbound socket splicing\n" - " --splice-only Only enable loopback forwarding\n"); + " --splice-only Only enable loopback forwarding\n" + " --pass-fds FDS Comma-separated list of fds to pass to\n" + " the spawned command\n"); passt_exit(status); } @@ -1183,6 +1185,63 @@ int conf_tap_fd(int argc, char **argv) return val; } +/** + * conf_pass_fds() - Read fds as supplied by --pass-fds command line option + * @argc: Argument count + * @argv: Command line options + * @fds: Array where we store the parsed fds + * @max_fds: Maximum size of the array + * + * Return: number of parsed fds, or -1 if option not specified + */ +int conf_pass_fds(int argc, char **argv, int *fds, int max_fds) +{ + const struct option opt[] = { { "pass-fds", required_argument, NULL, 33 }, + { 0 }, }; + const char *fdsarg = NULL; + int name, fds_cnt = 0; + int old_opterr; + + old_opterr = opterr; + opterr = 0; + optind = 0; + do { + name = getopt_long(argc, argv, "-:", opt, NULL); + if (name == 33) + fdsarg = optarg; + } while (name != -1); + opterr = old_opterr; + + if (!fdsarg) + return -1; + + while (*fdsarg) { + unsigned long val; + char *endptr; + + val = strtoul(fdsarg, &endptr, 10); + if (fdsarg == endptr) + die("Invalid --pass-fds option: %s", fdsarg); + + if (val > INT_MAX) + die("Invalid file descriptor in --pass-fds: %lu", val); + + if (fds_cnt >= max_fds) + die("Too many file descriptors in --pass-fds"); + + fds[fds_cnt++] = (int)val; + + if (*endptr == ',') + fdsarg = endptr + 1; + else if (*endptr == '\0') + fdsarg = endptr; + else + die("Invalid character in --pass-fds option: %s", fdsarg); + } + + return fds_cnt; +} + /** * conf_addr() - Configure guest address with -a option * @c: Execution context @@ -1331,6 +1390,7 @@ void conf(struct ctx *c, int argc, char **argv) {"stats", required_argument, NULL, 31 }, {"conf-path", required_argument, NULL, 'c' }, {"chroot-fallback", no_argument, NULL, 32 }, + {"pass-fds", required_argument, NULL, 33 }, { 0 }, }; const char *optstring = "+dqfel:hs:c:F:I:p:P:m:a:n:M:g:i:o:D:S:H:461t:u:T:U:"; @@ -1572,6 +1632,10 @@ void conf(struct ctx *c, int argc, char **argv) case 32: c->chroot_fallback = true; break; + case 33: + if (c->mode != MODE_PASTA) + die("--pass-fds is for pasta mode only"); + break; case 'd': c->debug = 1; c->quiet = 0; diff --git a/conf.h b/conf.h index 19bf9bc..3489f35 100644 --- a/conf.h +++ b/conf.h @@ -7,6 +7,7 @@ #define CONF_H enum passt_modes conf_mode(int argc, char *argv[]); +int conf_pass_fds(int argc, char **argv, int *fds, int max_fds); int conf_tap_fd(int argc, char **argv); void conf(struct ctx *c, int argc, char **argv); void conf_listen_handler(struct ctx *c, uint32_t events); diff --git a/isolation.c b/isolation.c index 94cbe7f..0632f7f 100644 --- a/isolation.c +++ b/isolation.c @@ -249,32 +249,72 @@ void isolate_initial(void) } /* - * isolate_fds() - Close leaked files, but not --fd, stdin, stdout, stderr + * isolate_fds() - Close leaked files, but not --fd, --pass-fds, standard streams * @argc: Argument count - * @argv: Command line options, as we need to skip any file given via --fd + * @argv: Command line options * * Should: - * - close all open files except for standard streams and the one from --fd + * - close all open files except for standard streams, --fd, and --pass-fds * - move the --fd descriptor out of the range 0-2 * * Return: new fd number for descriptor from --fd, or -1 if not specified */ int isolate_fds(int argc, char **argv) { - int fd, close_from = STDERR_FILENO + 1; + int prev_fd = STDERR_FILENO; // Keep standard streams + int fds[1024 + 1]; + int fds_cnt = 0; + int tap_fd; + int rc = 0; + + tap_fd = conf_tap_fd(argc, argv); + if (tap_fd >= 0 && tap_fd < 3) { + /* Move the passed fd to a more convenient location */ + int new_fd = fcntl(tap_fd, F_DUPFD, 3); + + if (new_fd < 0) + die_perror("Could not relocate --fd descriptor"); - fd = conf_tap_fd(argc, argv); + close(tap_fd); + tap_fd = new_fd; + } - if (fd >= 0) { - /* Move the passed fd to a more convenient location */ - if (fd != close_from && - (dup2(fd, close_from) != close_from || - close(fd))) - die_perror("Could not move --fd descriptor"); - fd = close_from++; + if (tap_fd >= 0) + /* Keep the tap fd */ + fds[fds_cnt++] = tap_fd; + + rc = conf_pass_fds(argc, argv, fds + fds_cnt, 1024); + if (rc > 0) + /* Keep the pass-fds */ + fds_cnt += rc; + + rc = 0; + + while (1) { + int min_fd = -1; + + /* Find the next-lowest fd to keep */ + for (int i = 0; i < fds_cnt; i++) { + if (fds[i] > prev_fd && (min_fd == -1 || fds[i] < min_fd)) + min_fd = fds[i]; + } + + if (min_fd == -1) + break; + + if (min_fd > prev_fd + 1) { + /* Close fds between two kept fds */ + if (close_range(prev_fd + 1, min_fd - 1, CLOSE_RANGE_UNSHARE)) + rc = -1; + } + prev_fd = min_fd; } + + /* Close all other fds */ + if (close_range(prev_fd + 1, ~0U, CLOSE_RANGE_UNSHARE)) + rc = -1; - if (close_range(close_from, ~0U, CLOSE_RANGE_UNSHARE)) { + if (rc) { if (errno == ENOSYS || errno == EINVAL) { /* This probably means close_range() or the * CLOSE_RANGE_UNSHARE flag is not supported by the @@ -288,7 +328,7 @@ int isolate_fds(int argc, char **argv) } } - return fd; + return tap_fd; } /** diff --git a/passt.1 b/passt.1 index 995590a..bcd3aff 100644 --- a/passt.1 +++ b/passt.1 @@ -755,6 +755,11 @@ of local traffic in pasta\fR in the \fBNOTES\fR for more details. Do not create a tap device in the namespace. In this mode, \fIpasta\fR only forwards loopback traffic between namespaces. +.TP +.BR \-\-pass\-fds " " \fIfds\fR +Pass a comma-separated list of file descriptors to the spawned command. +These file descriptors will be kept open. + .SH EXAMPLES .SS \fBpasta -- 2.52.0 [-- Attachment #2: Type: text/html, Size: 25379 bytes --] ^ permalink raw reply [flat|nested] 3+ messages in thread
end of thread, other threads:[~2026-07-19 19:14 UTC | newest] Thread overview: 3+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2026-07-18 16:14 [PATCH v2] feat: Add cli option '--pass-fds' for pasta mode Richard Lawrence 2026-07-18 16:52 ` Lawrence, Richard E 2026-07-19 19:14 ` Lawrence, Richard E
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