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port_fwd: Pre-open /proc/net/* files rather than on-demand

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procfs_scan_listen() can either use an already opened fd for a /proc/net
file, or it will open it.  So, effectively it will open the file on the
first call, then re-use the fd in subsequent calls.  However, it's not
possible to open the /proc/net files after we isolate our filesystem in
isolate_prefork().  That means that for each /proc/net file we must call
procfs_scan_listen() at least once before isolate_prefork(), or it won't
work afterwards.

That happens to be the case, but it's a pretty fragile requirement.  To
make this more robust, instead always pre-open the /proc files we will need
in get_bounds_port_init() and have procfs_scan_listen() just use those.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
This commit is contained in:
David Gibson 2023-11-03 13:22:59 +11:00 committed by Stefano Brivio
parent 4f0b9f91e4
commit 5a0485425b
1 changed files with 24 additions and 18 deletions
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42
port_fwd.c
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@ -29,8 +29,7 @@
/**
* procfs_scan_listen() - Set bits for listening TCP or UDP sockets from procfs
* @fd: Pointer to fd for relevant /proc/net file
* @path: Path to /proc/net file to open (if fd is -1)
* @fd: fd for relevant /proc/net file
* @lstate: Code for listening state to scan for
* @map: Bitmap where numbers of ports in listening state will be set
* @exclude: Bitmap of ports to exclude from setting (and clear)
@ -38,7 +37,7 @@
* #syscalls:pasta lseek
* #syscalls:pasta ppc64le:_llseek ppc64:_llseek armv6l:_llseek armv7l:_llseek
*/
static void procfs_scan_listen(int *fd, const char *path, unsigned int lstate,
static void procfs_scan_listen(int fd, unsigned int lstate,
uint8_t *map, const uint8_t *exclude)
{
struct lineread lr;
@ -46,16 +45,12 @@ static void procfs_scan_listen(int *fd, const char *path, unsigned int lstate,
unsigned int state;
char *line;
if (*fd != -1) {
if (lseek(*fd, 0, SEEK_SET)) {
warn("lseek() failed on %s: %s", path, strerror(errno));
return;
}
} else if ((*fd = open(path, O_RDONLY | O_CLOEXEC)) < 0) {
if (lseek(fd, 0, SEEK_SET)) {
warn("lseek() failed on /proc/net file: %s", strerror(errno));
return;
}
lineread_init(&lr, *fd);
lineread_init(&lr, fd);
lineread_get(&lr, &line); /* throw away header */
while (lineread_get(&lr, &line) > 0) {
/* NOLINTNEXTLINE(cert-err34-c): != 2 if conversion fails */
@ -96,20 +91,20 @@ void get_bound_ports(struct ctx *c, int ns, uint8_t proto)
if (proto == IPPROTO_UDP) {
memset(udp_map, 0, PORT_BITMAP_SIZE);
procfs_scan_listen(&c->proc_net_udp[V4][ns], "/proc/net/udp",
procfs_scan_listen(c->proc_net_udp[V4][ns],
UDP_LISTEN, udp_map, udp_excl);
procfs_scan_listen(&c->proc_net_udp[V6][ns], "/proc/net/udp6",
procfs_scan_listen(c->proc_net_udp[V6][ns],
UDP_LISTEN, udp_map, udp_excl);
procfs_scan_listen(&c->proc_net_tcp[V4][ns], "/proc/net/tcp",
procfs_scan_listen(c->proc_net_tcp[V4][ns],
TCP_LISTEN, udp_map, udp_excl);
procfs_scan_listen(&c->proc_net_tcp[V6][ns], "/proc/net/tcp6",
procfs_scan_listen(c->proc_net_tcp[V6][ns],
TCP_LISTEN, udp_map, udp_excl);
} else if (proto == IPPROTO_TCP) {
memset(tcp_map, 0, PORT_BITMAP_SIZE);
procfs_scan_listen(&c->proc_net_tcp[V4][ns], "/proc/net/tcp",
procfs_scan_listen(c->proc_net_tcp[V4][ns],
TCP_LISTEN, tcp_map, tcp_excl);
procfs_scan_listen(&c->proc_net_tcp[V6][ns], "/proc/net/tcp6",
procfs_scan_listen(c->proc_net_tcp[V6][ns],
TCP_LISTEN, tcp_map, tcp_excl);
}
}
@ -151,6 +146,7 @@ static int get_bound_ports_ns(void *arg)
void port_fwd_init(struct ctx *c)
{
struct get_bound_ports_ns_arg ns_ports_arg = { .c = c };
const int flags = O_RDONLY | O_CLOEXEC;
c->proc_net_tcp[V4][0] = c->proc_net_tcp[V4][1] = -1;
c->proc_net_tcp[V6][0] = c->proc_net_tcp[V6][1] = -1;
@ -158,15 +154,25 @@ void port_fwd_init(struct ctx *c)
c->proc_net_udp[V6][0] = c->proc_net_udp[V6][1] = -1;
if (c->tcp.fwd_in.mode == FWD_AUTO) {
c->proc_net_tcp[V4][1] = open_in_ns(c, "/proc/net/tcp", flags);
c->proc_net_tcp[V6][1] = open_in_ns(c, "/proc/net/tcp6", flags);
ns_ports_arg.proto = IPPROTO_TCP;
NS_CALL(get_bound_ports_ns, &ns_ports_arg);
}
if (c->udp.fwd_in.f.mode == FWD_AUTO) {
c->proc_net_udp[V4][1] = open_in_ns(c, "/proc/net/udp", flags);
c->proc_net_udp[V6][1] = open_in_ns(c, "/proc/net/udp6", flags);
ns_ports_arg.proto = IPPROTO_UDP;
NS_CALL(get_bound_ports_ns, &ns_ports_arg);
}
if (c->tcp.fwd_out.mode == FWD_AUTO)
if (c->tcp.fwd_out.mode == FWD_AUTO) {
c->proc_net_tcp[V4][0] = open("/proc/net/tcp", flags);
c->proc_net_tcp[V6][0] = open("/proc/net/tcp6", flags);
get_bound_ports(c, 0, IPPROTO_TCP);
if (c->udp.fwd_out.f.mode == FWD_AUTO)
}
if (c->udp.fwd_out.f.mode == FWD_AUTO) {
c->proc_net_udp[V4][0] = open("/proc/net/udp", flags);
c->proc_net_udp[V6][0] = open("/proc/net/udp6", flags);
get_bound_ports(c, 0, IPPROTO_UDP);
}
}