From 054669a4cc4897792b6c209fd55ab1fc1d7b9bd5 Mon Sep 17 00:00:00 2001
From: Lennart Poettering <lennart@poettering.net>
Date: Fri, 17 Jul 2020 12:26:01 +0200
Subject: [PATCH] fileio: add support for read_full_file() on AF_UNIX stream
 sockets

Optionally, teach read_full_file() the ability to connect to an AF_UNIX
socket if the specified path points to one.

(cherry picked from commit 412b888ec803cdf96fb1d005bb245d20abdb8f2e)

[Guorui Yu: Adds sockaddr_un_set_path function to socket-util.{c,h}]
Signed-off-by: Guorui Yu <GuoRui.Yu@linux.alibaba.com>
---
 src/basic/fileio.c      | 62 +++++++++++++++++++++++++++++++++++------
 src/basic/fileio.h      |  1 +
 src/basic/socket-util.c | 42 ++++++++++++++++++++++++++++
 src/basic/socket-util.h |  1 +
 src/test/test-fileio.c  | 50 +++++++++++++++++++++++++++++++++
 5 files changed, 147 insertions(+), 9 deletions(-)

diff --git a/src/basic/fileio.c b/src/basic/fileio.c
index d7da834a74..9cb0a2bd28 100644
--- a/src/basic/fileio.c
+++ b/src/basic/fileio.c
@@ -27,6 +27,7 @@
 #include "missing.h"
 #include "parse-util.h"
 #include "path-util.h"
+#include "socket-util.h"
 #include "process-util.h"
 #include "random-util.h"
 #include "stdio-util.h"
@@ -450,21 +451,18 @@ int read_full_stream_full(
 
                 errno = 0;
                 k = fread(buf + l, 1, n - l, f);
-                if (k > 0)
-                        l += k;
+
+                assert(k <= n - l);
+                l += k;
 
                 if (ferror(f)) {
                         r = errno > 0 ? -errno : -EIO;
                         goto finalize;
                 }
-
                 if (feof(f))
                         break;
 
-                /* We aren't expecting fread() to return a short read outside
-                 * of (error && eof), assert buffer is full and enlarge buffer.
-                 */
-                assert(l == n);
+                assert(k > 0); /* we can't have read zero bytes because that would have been EOF */
 
                 /* Safety check */
                 if (n >= READ_FULL_BYTES_MAX) {
@@ -584,8 +582,54 @@ int read_full_file_full(int dir_fd, const char *filename, ReadFullFileFlags flag
         assert(contents);
 
         r = xfopenat(dir_fd, filename, "re", 0, &f);
-        if (r < 0)
-                return r;
+        if (r < 0) {
+                _cleanup_close_ int dfd = -1, sk = -1;
+                union sockaddr_union sa;
+
+                /* ENXIO is what Linux returns if we open a node that is an AF_UNIX socket */
+                if (r != -ENXIO)
+                        return r;
+
+                /* If this is enabled, let's try to connect to it */
+                if (!FLAGS_SET(flags, READ_FULL_FILE_CONNECT_SOCKET))
+                        return -ENXIO;
+
+                if (dir_fd == AT_FDCWD)
+                        r = sockaddr_un_set_path(&sa.un, filename);
+                else {
+                        char procfs_path[STRLEN("/proc/self/fd/") + DECIMAL_STR_MAX(int)];
+
+                        /* If we shall operate relative to some directory, then let's use O_PATH first to
+                         * open the socket inode, and then connect to it via /proc/self/fd/. We have to do
+                         * this since there's not connectat() that takes a directory fd as first arg. */
+
+                        dfd = openat(dir_fd, filename, O_PATH|O_CLOEXEC);
+                        if (dfd < 0)
+                                return -errno;
+
+                        xsprintf(procfs_path, "/proc/self/fd/%i", dfd);
+                        r = sockaddr_un_set_path(&sa.un, procfs_path);
+                }
+                if (r < 0)
+                        return r;
+
+                sk = socket(AF_UNIX, SOCK_STREAM|SOCK_CLOEXEC, 0);
+                if (sk < 0)
+                        return -errno;
+
+                if (connect(sk, &sa.sa, SOCKADDR_UN_LEN(sa.un)) < 0)
+                        return errno == ENOTSOCK ? -ENXIO : -errno; /* propagate original error if this is
+                                                                     * not a socket after all */
+
+                if (shutdown(sk, SHUT_WR) < 0)
+                        return -errno;
+
+                f = fdopen(sk, "r");
+                if (!f)
+                        return -errno;
+
+                TAKE_FD(sk);
+        }
 
         (void) __fsetlocking(f, FSETLOCKING_BYCALLER);
 
diff --git a/src/basic/fileio.h b/src/basic/fileio.h
index 916ddc5e47..1a16e0fd13 100644
--- a/src/basic/fileio.h
+++ b/src/basic/fileio.h
@@ -29,6 +29,7 @@ typedef enum {
 typedef enum {
         READ_FULL_FILE_SECURE              = 1 << 0,
         READ_FULL_FILE_WARN_WORLD_READABLE = 1 << 3,
+        READ_FULL_FILE_CONNECT_SOCKET      = 1 << 4,
 } ReadFullFileFlags;
 
 int write_string_stream_ts(FILE *f, const char *line, WriteStringFileFlags flags, struct timespec *ts);
diff --git a/src/basic/socket-util.c b/src/basic/socket-util.c
index 7f8066123b..427c8b89bb 100644
--- a/src/basic/socket-util.c
+++ b/src/basic/socket-util.c
@@ -1253,6 +1253,48 @@ int socket_ioctl_fd(void) {
         return fd;
 }
 
+int sockaddr_un_set_path(struct sockaddr_un *ret, const char *path) {
+        size_t l;
+
+        assert(ret);
+        assert(path);
+
+        /* Initialize ret->sun_path from the specified argument. This will interpret paths starting with '@' as
+         * abstract namespace sockets, and those starting with '/' as regular filesystem sockets. It won't accept
+         * anything else (i.e. no relative paths), to avoid ambiguities. Note that this function cannot be used to
+         * reference paths in the abstract namespace that include NUL bytes in the name. */
+
+        l = strlen(path);
+        if (l < 2)
+                return -EINVAL;
+        if (!IN_SET(path[0], '/', '@'))
+                return -EINVAL;
+
+        /* Don't allow paths larger than the space in sockaddr_un. Note that we are a tiny bit more restrictive than
+         * the kernel is: we insist on NUL termination (both for abstract namespace and regular file system socket
+         * addresses!), which the kernel doesn't. We do this to reduce chance of incompatibility with other apps that
+         * do not expect non-NUL terminated file system path*/
+        if (l+1 > sizeof(ret->sun_path))
+                return -EINVAL;
+
+        *ret = (struct sockaddr_un) {
+                .sun_family = AF_UNIX,
+        };
+
+        if (path[0] == '@') {
+                /* Abstract namespace socket */
+                memcpy(ret->sun_path + 1, path + 1, l); /* copy *with* trailing NUL byte */
+                return (int) (offsetof(struct sockaddr_un, sun_path) + l); /* 🔥 *don't* 🔥 include trailing NUL in size */
+
+        } else {
+                assert(path[0] == '/');
+
+                /* File system socket */
+                memcpy(ret->sun_path, path, l + 1); /* copy *with* trailing NUL byte */
+                return (int) (offsetof(struct sockaddr_un, sun_path) + l + 1); /* include trailing NUL in size */
+        }
+}
+
 int socket_pass_pktinfo(int fd, bool b) {
         int af;
         socklen_t sl = sizeof(af);
diff --git a/src/basic/socket-util.h b/src/basic/socket-util.h
index 30baba6c03..36edc58caf 100644
--- a/src/basic/socket-util.h
+++ b/src/basic/socket-util.h
@@ -186,6 +186,7 @@ struct cmsghdr* cmsg_find(struct msghdr *mh, int level, int type, socklen_t leng
         })
 
 int socket_ioctl_fd(void);
+int sockaddr_un_set_path(struct sockaddr_un *ret, const char *path);
 
 static inline int setsockopt_int(int fd, int level, int optname, int value) {
         if (setsockopt(fd, level, optname, &value, sizeof(value)) < 0)
diff --git a/src/test/test-fileio.c b/src/test/test-fileio.c
index 14ba075144..82b7cb1242 100644
--- a/src/test/test-fileio.c
+++ b/src/test/test-fileio.c
@@ -14,6 +14,8 @@
 #include "io-util.h"
 #include "parse-util.h"
 #include "process-util.h"
+#include "rm-rf.h"
+#include "socket-util.h"
 #include "string-util.h"
 #include "strv.h"
 #include "util.h"
@@ -709,6 +711,53 @@ static void test_read_line3(void) {
         assert_se(read_line(f, LINE_MAX, NULL) == 0);
 }
 
+static void test_read_full_file_socket(void) {
+        _cleanup_(rm_rf_physical_and_freep) char *z = NULL;
+        _cleanup_close_ int listener = -1;
+        _cleanup_free_ char *data = NULL;
+        union sockaddr_union sa;
+        const char *j;
+        size_t size;
+        pid_t pid;
+        int r;
+
+        log_info("/* %s */", __func__);
+
+        listener = socket(AF_UNIX, SOCK_STREAM|SOCK_CLOEXEC, 0);
+        assert_se(listener >= 0);
+
+        assert_se(mkdtemp_malloc(NULL, &z) >= 0);
+        j = strjoina(z, "/socket");
+
+        assert_se(sockaddr_un_set_path(&sa.un, j) >= 0);
+
+        assert_se(bind(listener, &sa.sa, SOCKADDR_UN_LEN(sa.un)) >= 0);
+        assert_se(listen(listener, 1) >= 0);
+
+        r = safe_fork("(server)", FORK_DEATHSIG|FORK_LOG, &pid);
+        assert_se(r >= 0);
+        if (r == 0) {
+                _cleanup_close_ int rfd = -1;
+                /* child */
+
+                rfd = accept4(listener, NULL, 0, SOCK_CLOEXEC);
+                assert_se(rfd >= 0);
+
+#define TEST_STR "This is a test\nreally."
+
+                assert_se(write(rfd, TEST_STR, strlen(TEST_STR)) == strlen(TEST_STR));
+                _exit(EXIT_SUCCESS);
+        }
+
+        assert_se(read_full_file_full(AT_FDCWD, j, 0, &data, &size) == -ENXIO);
+        assert_se(read_full_file_full(AT_FDCWD, j, READ_FULL_FILE_CONNECT_SOCKET, &data, &size) >= 0);
+        assert_se(size == strlen(TEST_STR));
+        assert_se(streq(data, TEST_STR));
+
+        assert_se(wait_for_terminate_and_check("(server)", pid, WAIT_LOG) >= 0);
+#undef TEST_STR
+}
+
 int main(int argc, char *argv[]) {
         log_set_max_level(LOG_DEBUG);
         log_parse_environment();
@@ -733,6 +782,7 @@ int main(int argc, char *argv[]) {
         test_read_line();
         test_read_line2();
         test_read_line3();
+        test_read_full_file_socket();
 
         return 0;
 }
-- 
2.39.1