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>
This commit is contained in:
Tristan Schmelcher 2013-07-08 16:19:49 -04:00 committed by Richard Weinberger
parent 0974a9cadc
commit 7473534130

View file

@ -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);
}
/*
* 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 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);
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,