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main: Override inaccessible xattrs
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Signed-off-by: Akihiko Odaki <odaki@rsg.ci.i.u-tokyo.ac.jp>
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@akihikodaki
akihikodaki committed Jun 14, 2024
1 parent d498816 commit 2267664
Showing 1 changed file with 80 additions and 23 deletions.
103 changes: 80 additions & 23 deletions main.c
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Original file line number Diff line number Diff line change
Expand Up @@ -141,6 +141,7 @@ open_by_handle_at (int mount_fd, struct file_handle *handle, int flags)
#define ORIGIN_XATTR "user.fuseoverlayfs.origin"
#define OPAQUE_XATTR "user.fuseoverlayfs.opaque"
#define XATTR_CONTAINERS_PREFIX "user.containers."
#define XATTR_CONTAINERS_OVERRIDE_PREFIX "user.containers.override_"
#define UNPRIVILEGED_XATTR_PREFIX "user.overlay."
#define UNPRIVILEGED_OPAQUE_XATTR "user.overlay.opaque"
#define PRIVILEGED_XATTR_PREFIX "trusted.overlay."
Expand Down Expand Up @@ -531,6 +532,39 @@ can_access_xattr (const char *name)
&& ! has_prefix (name, UNPRIVILEGED_XATTR_PREFIX);
}

static bool encoded_xattr_name (const char *name)
{
return has_prefix (name, XATTR_CONTAINERS_OVERRIDE_PREFIX) &&
! can_access_xattr (name + sizeof(XATTR_CONTAINERS_OVERRIDE_PREFIX) - 1);
}

static const char *decode_xattr_name (const char *name)
{
if (encoded_xattr_name (name))
return name + sizeof(XATTR_CONTAINERS_OVERRIDE_PREFIX) - 1;

if (can_access_xattr (name))
return name;

return NULL;
}

static const char *encode_xattr_name (const struct ovl_layer *l, char *buf,
const char *name)
{
if (can_access_xattr (name))
return name;

if (l->stat_override_mode != STAT_OVERRIDE_CONTAINERS ||
strlen(name) > XATTR_NAME_MAX + 1 - sizeof(XATTR_CONTAINERS_OVERRIDE_PREFIX))
return NULL;

strcpy(buf, XATTR_CONTAINERS_OVERRIDE_PREFIX);
strcpy(buf + sizeof(XATTR_CONTAINERS_OVERRIDE_PREFIX) - 1, name);

return buf;
}

static ssize_t
write_permission_xattr (struct ovl_data *lo, int fd, const char *path, uid_t uid, gid_t gid, mode_t mode)
{
Expand Down Expand Up @@ -2606,7 +2640,10 @@ filter_xattrs_list (char *buf, ssize_t len)
}
else
{
char *next = it + it_len;
char *next = it;

next += encoded_xattr_name (it) ?
sizeof(XATTR_CONTAINERS_OVERRIDE_PREFIX) - 1 : it_len;

memmove (it, next, buf + len - next);
len -= it_len;
Expand Down Expand Up @@ -2681,7 +2718,8 @@ ovl_getxattr (fuse_req_t req, fuse_ino_t ino, const char *name, size_t size)
ssize_t len;
struct ovl_node *node;
struct ovl_data *lo = ovl_data (req);
cleanup_free char *buf = NULL;
cleanup_free char *value_buf = NULL;
char name_buf[XATTR_NAME_MAX + 1];
int ret;

if (UNLIKELY (ovl_debug (req)))
Expand All @@ -2693,36 +2731,37 @@ ovl_getxattr (fuse_req_t req, fuse_ino_t ino, const char *name, size_t size)
return;
}

if (! can_access_xattr (name))
node = do_lookup_file (lo, ino, NULL);
if (node == NULL || node->whiteout)
{
fuse_reply_err (req, ENODATA);
fuse_reply_err (req, ENOENT);
return;
}

node = do_lookup_file (lo, ino, NULL);
if (node == NULL || node->whiteout)
name = encode_xattr_name (node->layer, name_buf, name);
if (!name)
{
fuse_reply_err (req, ENOENT);
fuse_reply_err (req, ENODATA);
return;
}

if (size > 0)
{
buf = malloc (size);
if (buf == NULL)
value_buf = malloc (size);
if (value_buf == NULL)
{
fuse_reply_err (req, errno);
return;
}
}

if (! node->hidden)
ret = node->layer->ds->getxattr (node->layer, node->path, name, buf, size);
ret = node->layer->ds->getxattr (node->layer, node->path, name, value_buf, size);
else
{
char path[PATH_MAX];
strconcat3 (path, PATH_MAX, lo->workdir, "/", node->path);
ret = getxattr (path, name, buf, size);
ret = getxattr (path, name, value_buf, size);
}

if (ret < 0)
Expand All @@ -2736,7 +2775,7 @@ ovl_getxattr (fuse_req_t req, fuse_ino_t ino, const char *name, size_t size)
if (size == 0)
fuse_reply_xattr (req, len);
else
fuse_reply_buf (req, buf, len);
fuse_reply_buf (req, value_buf, len);
}

static void
Expand All @@ -2757,7 +2796,8 @@ ovl_access (fuse_req_t req, fuse_ino_t ino, int mask)
}

static int
copy_xattr (int sfd, int dfd, char *buf, size_t buf_size)
copy_xattr (int sfd,
const struct ovl_layer *dl, int dfd, char *buf, size_t buf_size)
{
ssize_t xattr_len;

Expand All @@ -2768,9 +2808,16 @@ copy_xattr (int sfd, int dfd, char *buf, size_t buf_size)
for (it = buf; it - buf < xattr_len; it += strlen (it) + 1)
{
cleanup_free char *v = NULL;
const char *decoded_name = decode_xattr_name (it);
const char *encoded_name;
char buf[XATTR_NAME_MAX + 1];
ssize_t s;

if (! can_access_xattr (it))
if (! decoded_name)
continue;

encoded_name = encode_xattr_name (dl, buf, decoded_name);
if (! encoded_name)
continue;

s = safe_read_xattr (&v, sfd, it, 256);
Expand All @@ -2781,7 +2828,7 @@ copy_xattr (int sfd, int dfd, char *buf, size_t buf_size)
return -1;
}

if (fsetxattr (dfd, it, v, s, 0) < 0)
if (fsetxattr (dfd, encoded_name, v, s, 0) < 0)
{
if (errno == EINVAL || errno == EOPNOTSUPP)
continue;
Expand Down Expand Up @@ -2921,7 +2968,7 @@ create_directory (struct ovl_data *lo, int dirfd, const char *name, const struct
goto out;
}

ret = copy_xattr (xattr_sfd, dfd, buf, buf_size);
ret = copy_xattr (xattr_sfd, get_upper_layer (lo), dfd, buf, buf_size);
if (ret < 0)
goto out;
}
Expand Down Expand Up @@ -3193,7 +3240,7 @@ copyup (struct ovl_data *lo, struct ovl_node *node)
if (ret < 0)
goto exit;

ret = copy_xattr (sfd, dfd, buf, buf_size);
ret = copy_xattr (sfd, get_upper_layer (lo), dfd, buf, buf_size);
if (ret < 0)
goto exit;

Expand Down Expand Up @@ -3473,6 +3520,7 @@ ovl_setxattr (fuse_req_t req, fuse_ino_t ino, const char *name,
cleanup_lock int l = enter_big_lock ();
struct ovl_data *lo = ovl_data (req);
struct ovl_node *node;
char name_buf[XATTR_NAME_MAX + 1];
int ret;

if (UNLIKELY (ovl_debug (req)))
Expand All @@ -3485,12 +3533,6 @@ ovl_setxattr (fuse_req_t req, fuse_ino_t ino, const char *name,
return;
}

if (has_prefix (name, PRIVILEGED_XATTR_PREFIX) || has_prefix (name, XATTR_PREFIX) || has_prefix (name, XATTR_CONTAINERS_PREFIX))
{
fuse_reply_err (req, EPERM);
return;
}

node = do_lookup_file (lo, ino, NULL);
if (node == NULL || node->whiteout)
{
Expand All @@ -3505,6 +3547,13 @@ ovl_setxattr (fuse_req_t req, fuse_ino_t ino, const char *name,
return;
}

name = encode_xattr_name (node->layer, name_buf, name);
if (!name)
{
fuse_reply_err (req, EPERM);
return;
}

if (! node->hidden)
ret = direct_setxattr (node->layer, node->path, name, value, size, flags);
else
Expand Down Expand Up @@ -3546,6 +3595,7 @@ ovl_removexattr (fuse_req_t req, fuse_ino_t ino, const char *name)
cleanup_lock int l = enter_big_lock ();
struct ovl_node *node;
struct ovl_data *lo = ovl_data (req);
char name_buf[XATTR_NAME_MAX + 1];
int ret;

if (UNLIKELY (ovl_debug (req)))
Expand All @@ -3565,6 +3615,13 @@ ovl_removexattr (fuse_req_t req, fuse_ino_t ino, const char *name)
return;
}

name = encode_xattr_name (node->layer, name_buf, name);
if (!name)
{
fuse_reply_err (req, EPERM);
return;
}

if (! node->hidden)
ret = direct_removexattr (node->layer, node->path, name);
else
Expand Down

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