[3621] | 1 | /*
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| 2 | * Copyright 2015 Denys Vlasenko
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| 3 | *
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| 4 | * Licensed under GPLv2, see file LICENSE in this source tree.
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| 5 | */
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| 6 |
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| 7 | //config:config UEVENT
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| 8 | //config: bool "uevent"
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| 9 | //config: default y
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| 10 | //config: select PLATFORM_LINUX
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| 11 | //config: help
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| 12 | //config: uevent is a netlink listener for kernel uevent notifications
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| 13 | //config: sent via netlink. It is usually used for dynamic device creation.
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| 14 |
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| 15 | //applet:IF_UEVENT(APPLET(uevent, BB_DIR_SBIN, BB_SUID_DROP))
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| 16 |
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| 17 | //kbuild:lib-$(CONFIG_UEVENT) += uevent.o
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| 18 |
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| 19 | //usage:#define uevent_trivial_usage
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| 20 | //usage: "[PROG [ARGS]]"
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| 21 | //usage:#define uevent_full_usage "\n\n"
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| 22 | //usage: "uevent runs PROG for every netlink notification."
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| 23 | //usage: "\n""PROG's environment contains data passed from the kernel."
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| 24 | //usage: "\n""Typical usage (daemon for dynamic device node creation):"
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| 25 | //usage: "\n"" # uevent mdev & mdev -s"
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| 26 |
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| 27 | #include "libbb.h"
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| 28 | #include "common_bufsiz.h"
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| 29 | #include <linux/netlink.h>
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| 30 |
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| 31 | #define BUFFER_SIZE 16*1024
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| 32 |
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| 33 | #define env ((char **)bb_common_bufsiz1)
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| 34 | #define INIT_G() do { setup_common_bufsiz(); } while (0)
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| 35 | enum {
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| 36 | MAX_ENV = COMMON_BUFSIZE / sizeof(env[0]) - 1,
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| 37 | };
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| 38 |
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| 39 | #ifndef SO_RCVBUFFORCE
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| 40 | #define SO_RCVBUFFORCE 33
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| 41 | #endif
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| 42 | enum { RCVBUF = 2 * 1024 * 1024 };
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| 43 |
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| 44 | int uevent_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
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| 45 | int uevent_main(int argc UNUSED_PARAM, char **argv)
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| 46 | {
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| 47 | struct sockaddr_nl sa;
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| 48 | int fd;
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| 49 |
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| 50 | INIT_G();
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| 51 |
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| 52 | argv++;
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| 53 |
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| 54 | // Subscribe for UEVENT kernel messages
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| 55 | sa.nl_family = AF_NETLINK;
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| 56 | sa.nl_pad = 0;
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| 57 | sa.nl_pid = getpid();
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| 58 | sa.nl_groups = 1 << 0;
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| 59 | fd = xsocket(AF_NETLINK, SOCK_DGRAM, NETLINK_KOBJECT_UEVENT);
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| 60 | xbind(fd, (struct sockaddr *) &sa, sizeof(sa));
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| 61 | close_on_exec_on(fd);
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| 62 |
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| 63 | // Without a sufficiently big RCVBUF, a ton of simultaneous events
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| 64 | // can trigger ENOBUFS on read, which is unrecoverable.
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| 65 | // Reproducer:
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| 66 | // uevent mdev &
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| 67 | // find /sys -name uevent -exec sh -c 'echo add >"{}"' ';'
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| 68 | //
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| 69 | // SO_RCVBUFFORCE (root only) can go above net.core.rmem_max sysctl
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| 70 | setsockopt_SOL_SOCKET_int(fd, SO_RCVBUF, RCVBUF);
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| 71 | setsockopt_SOL_SOCKET_int(fd, SO_RCVBUFFORCE, RCVBUF);
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| 72 | if (0) {
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| 73 | int z;
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| 74 | socklen_t zl = sizeof(z);
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| 75 | getsockopt(fd, SOL_SOCKET, SO_RCVBUF, &z, &zl);
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| 76 | bb_error_msg("SO_RCVBUF:%d", z);
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| 77 | }
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| 78 |
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| 79 | for (;;) {
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| 80 | char *netbuf;
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| 81 | char *s, *end;
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| 82 | ssize_t len;
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| 83 | int idx;
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| 84 |
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| 85 | // In many cases, a system sits for *days* waiting
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| 86 | // for a new uevent notification to come in.
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| 87 | // We use a fresh mmap so that buffer is not allocated
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| 88 | // until kernel actually starts filling it.
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| 89 | netbuf = mmap(NULL, BUFFER_SIZE,
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| 90 | PROT_READ | PROT_WRITE,
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| 91 | MAP_PRIVATE | MAP_ANON,
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| 92 | /* ignored: */ -1, 0);
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| 93 | if (netbuf == MAP_FAILED)
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| 94 | bb_perror_msg_and_die("mmap");
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| 95 |
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| 96 | // Here we block, possibly for a very long time
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| 97 | len = safe_read(fd, netbuf, BUFFER_SIZE - 1);
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| 98 | if (len < 0)
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| 99 | bb_perror_msg_and_die("read");
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| 100 | end = netbuf + len;
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| 101 | *end = '\0';
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| 102 |
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| 103 | // Each netlink message starts with "ACTION@/path"
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| 104 | // (which we currently ignore),
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| 105 | // followed by environment variables.
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| 106 | if (!argv[0])
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| 107 | putchar('\n');
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| 108 | idx = 0;
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| 109 | s = netbuf;
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| 110 | while (s < end) {
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| 111 | if (!argv[0])
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| 112 | puts(s);
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| 113 | if (strchr(s, '=') && idx < MAX_ENV)
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| 114 | env[idx++] = s;
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| 115 | s += strlen(s) + 1;
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| 116 | }
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| 117 | env[idx] = NULL;
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| 118 |
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| 119 | idx = 0;
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| 120 | while (env[idx])
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| 121 | putenv(env[idx++]);
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| 122 | if (argv[0])
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| 123 | spawn_and_wait(argv);
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| 124 | idx = 0;
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| 125 | while (env[idx])
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| 126 | bb_unsetenv(env[idx++]);
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| 127 | munmap(netbuf, BUFFER_SIZE);
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| 128 | }
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| 129 |
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| 130 | return 0; // not reached
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| 131 | }
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