uml: Fix which_tmpdir failure when /dev/shm is a symlink, and in other edge cases
which_tmpdir did the wrong thing if /dev/shm was a symlink (e.g., to /run/shm),
if there were multiple mounts on top of each other, if the mount(s) were
obscured by a later mount, or if /dev/shm was a prefix of another mount point.
This fixes these cases. Applies to 3.9.6.
Signed-off-by: Tristan Schmelcher <tschmelcher@google.com>
Signed-off-by: Richard Weinberger <richard@nod.at>
diff --git a/arch/um/os-Linux/mem.c b/arch/um/os-Linux/mem.c
index ba43980..3c4af77 100644
--- a/arch/um/os-Linux/mem.c
+++ b/arch/um/os-Linux/mem.c
@@ -53,6 +53,25 @@
}
/*
+ * 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
* read the file as needed. If there's an error, -errno is returned;
@@ -61,7 +80,6 @@
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 @@
buf[n] = '\0';
}
- ptr++;
- len = strlen(ptr);
- memmove(buf, ptr, len + 1);
+ return pop(fd, buf, size, ptr - buf + 1);
+}
+
+/*
+ * 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.
+ */
+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;
+
+ 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;
/*
- * Refill the buffer so that if there's a partial string that we care
- * about, it will be completed, and we can recognize it.
+ * 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.
*/
- n = read(fd, &buf[len], size - len - 1);
- if (n < 0)
- return -errno;
+ 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;
+ }
- buf[len + n] = '\0';
- return 1;
+ 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 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 @@
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);
+ case OUTCOME_NON_TMPFS_MOUNT:
+ printf("not tmpfs\n");
+ break;
- return;
-
-found:
- found = next(fd, buf, ARRAY_SIZE(buf), ' ');
- if (found != 1)
- goto err;
-
- if (strncmp(buf, "tmpfs", strlen("tmpfs"))) {
- printf("not tmpfs\n");
- goto out;
+ 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,