uml: Fix which_tmpdir failure when /dev/shm is a symlink, and in other edge cases (74735341) · Commits · 戴 / test

arch/um/os-Linux/mem.c

+189 −41

Original line number	Diff line number	Diff line
		@@ -52,6 +52,25 @@ static void __init find_tempdir(void)
		strcat(tempdir, "/");
		}

		/*
		* Remove bytes from the front of the buffer and refill it so that if there's a
		* partial string that we care about, it will be completed, and we can recognize
		* it.
		*/
		static int pop(int fd, char *buf, size_t size, size_t npop)
		{
		ssize_t n;
		size_t len = strlen(&buf[npop]);

		memmove(buf, &buf[npop], len + 1);
		n = read(fd, &buf[len], size - len - 1);
		if (n < 0)
		return -errno;

		buf[len + n] = '\0';
		return 1;
		}

		/*
		* This will return 1, with the first character in buf being the
		* character following the next instance of c in the file. This will
		@@ -61,7 +80,6 @@ static void __init find_tempdir(void)
		static int next(int fd, char *buf, size_t size, char c)
		{
		ssize_t n;
		size_t len;
		char *ptr;

		while ((ptr = strchr(buf, c)) == NULL) {
		@@ -74,20 +92,129 @@ static int next(int fd, char *buf, size_t size, char c)
		buf[n] = '\0';
		}

		ptr++;
		len = strlen(ptr);
		memmove(buf, ptr, len + 1);
		return pop(fd, buf, size, ptr - buf + 1);
		}

		/*
		* Refill the buffer so that if there's a partial string that we care
		* about, it will be completed, and we can recognize it.
		* Decode an octal-escaped and space-terminated path of the form used by
		* /proc/mounts. May be used to decode a path in-place. "out" must be at least
		* as large as the input. The output is always null-terminated. "len" gets the
		* length of the output, excluding the trailing null. Returns 0 if a full path
		* was successfully decoded, otherwise an error.
		*/
		n = read(fd, &buf[len], size - len - 1);
		if (n < 0)
		return -errno;
		static int decode_path(const char in, char out, size_t *len)
		{
		char *first = out;
		int c;
		int i;
		int ret = -EINVAL;
		while (1) {
		switch (*in) {
		case '\0':
		goto out;

		buf[len + n] = '\0';
		return 1;
		case ' ':
		ret = 0;
		goto out;

		case '\\':
		in++;
		c = 0;
		for (i = 0; i < 3; i++) {
		if (in < '0' \|\| in > '7')
		goto out;
		c = (c << 3) \| (*in++ - '0');
		}
		(unsigned char )out++ = (unsigned char) c;
		break;

		default:
		out++ = in++;
		break;
		}
		}

		out:
		*out = '\0';
		*len = out - first;
		return ret;
		}

		/*
		* Computes the length of s when encoded with three-digit octal escape sequences
		* for the characters in chars.
		*/
		static size_t octal_encoded_length(const char s, const char chars)
		{
		size_t len = strlen(s);
		while ((s = strpbrk(s, chars)) != NULL) {
		len += 3;
		s++;
		}

		return len;
		}

		enum {
		OUTCOME_NOTHING_MOUNTED,
		OUTCOME_TMPFS_MOUNT,
		OUTCOME_NON_TMPFS_MOUNT,
		};

		/* Read a line of /proc/mounts data looking for a tmpfs mount at "path". */
		static int read_mount(int fd, char buf, size_t bufsize, const char path,
		int *outcome)
		{
		int found;
		int match;
		char *space;
		size_t len;

		enum {
		MATCH_NONE,
		MATCH_EXACT,
		MATCH_PARENT,
		};

		found = next(fd, buf, bufsize, ' ');
		if (found != 1)
		return found;

		/*
		* If there's no following space in the buffer, then this path is
		* truncated, so it can't be the one we're looking for.
		*/
		space = strchr(buf, ' ');
		if (space) {
		match = MATCH_NONE;
		if (!decode_path(buf, buf, &len)) {
		if (!strcmp(buf, path))
		match = MATCH_EXACT;
		else if (!strncmp(buf, path, len)
		&& (path[len] == '/' \|\| !strcmp(buf, "/")))
		match = MATCH_PARENT;
		}

		found = pop(fd, buf, bufsize, space - buf + 1);
		if (found != 1)
		return found;

		switch (match) {
		case MATCH_EXACT:
		if (!strncmp(buf, "tmpfs", strlen("tmpfs")))
		*outcome = OUTCOME_TMPFS_MOUNT;
		else
		*outcome = OUTCOME_NON_TMPFS_MOUNT;
		break;

		case MATCH_PARENT:
		/* This mount obscures any previous ones. */
		*outcome = OUTCOME_NOTHING_MOUNTED;
		break;
		}
		}

		return next(fd, buf, bufsize, '\n');
		}

		/* which_tmpdir is called only during early boot */
		@@ -106,8 +233,12 @@ static int checked_tmpdir = 0;
		*/
		static void which_tmpdir(void)
		{
		int fd, found;
		char buf[128] = { '\0' };
		int fd;
		int found;
		int outcome;
		char *path;
		char *buf;
		size_t bufsize;

		if (checked_tmpdir)
		return;
		@@ -116,49 +247,66 @@ static void which_tmpdir(void)

		printf("Checking for tmpfs mount on /dev/shm...");

		path = realpath("/dev/shm", NULL);
		if (!path) {
		printf("failed to check real path, errno = %d\n", errno);
		return;
		}
		printf("%s...", path);

		/*
		* The buffer needs to be able to fit the full octal-escaped path, a
		* space, and a trailing null in order to successfully decode it.
		*/
		bufsize = octal_encoded_length(path, " \t\n\\") + 2;

		if (bufsize < 128)
		bufsize = 128;

		buf = malloc(bufsize);
		if (!buf) {
		printf("malloc failed, errno = %d\n", errno);
		goto out;
		}
		buf[0] = '\0';

		fd = open("/proc/mounts", O_RDONLY);
		if (fd < 0) {
		printf("failed to open /proc/mounts, errno = %d\n", errno);
		return;
		goto out1;
		}

		outcome = OUTCOME_NOTHING_MOUNTED;
		while (1) {
		found = next(fd, buf, ARRAY_SIZE(buf), ' ');
		if (found != 1)
		break;

		if (!strncmp(buf, "/dev/shm", strlen("/dev/shm")))
		goto found;

		found = next(fd, buf, ARRAY_SIZE(buf), '\n');
		found = read_mount(fd, buf, bufsize, path, &outcome);
		if (found != 1)
		break;
		}

		err:
		if (found == 0)
		printf("nothing mounted on /dev/shm\n");
		else if (found < 0)
		if (found < 0) {
		printf("read returned errno %d\n", -found);
		} else {
		switch (outcome) {
		case OUTCOME_TMPFS_MOUNT:
		printf("OK\n");
		default_tmpdir = "/dev/shm";
		break;

		out:
		close(fd);

		return;

		found:
		found = next(fd, buf, ARRAY_SIZE(buf), ' ');
		if (found != 1)
		goto err;

		if (strncmp(buf, "tmpfs", strlen("tmpfs"))) {
		case OUTCOME_NON_TMPFS_MOUNT:
		printf("not tmpfs\n");
		goto out;
		break;

		default:
		printf("nothing mounted on /dev/shm\n");
		break;
		}
		}

		printf("OK\n");
		default_tmpdir = "/dev/shm";
		goto out;
		close(fd);
		out1:
		free(buf);
		out:
		free(path);
		}

		static int __init make_tempfile(const char template, char *out_tempname,

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