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authorLinus Torvalds <torvalds@linux-foundation.org>2015-07-03 15:20:57 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2015-07-03 15:20:57 -0700
commit0cbee992696236227a7ea411e4b0fbf73b918b6a (patch)
treee84f0a8e64d64ff910e5b373537e4bd21e03f607 /fs/proc
parent2fee94b74b45681a09b1dac54cb615e02b7b30d0 (diff)
parent93e3bce6287e1fb3e60d3324ed08555b5bbafa89 (diff)
downloadlinux-0cbee992696236227a7ea411e4b0fbf73b918b6a.tar.bz2
Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace
Pull user namespace updates from Eric Biederman: "Long ago and far away when user namespaces where young it was realized that allowing fresh mounts of proc and sysfs with only user namespace permissions could violate the basic rule that only root gets to decide if proc or sysfs should be mounted at all. Some hacks were put in place to reduce the worst of the damage could be done, and the common sense rule was adopted that fresh mounts of proc and sysfs should allow no more than bind mounts of proc and sysfs. Unfortunately that rule has not been fully enforced. There are two kinds of gaps in that enforcement. Only filesystems mounted on empty directories of proc and sysfs should be ignored but the test for empty directories was insufficient. So in my tree directories on proc, sysctl and sysfs that will always be empty are created specially. Every other technique is imperfect as an ordinary directory can have entries added even after a readdir returns and shows that the directory is empty. Special creation of directories for mount points makes the code in the kernel a smidge clearer about it's purpose. I asked container developers from the various container projects to help test this and no holes were found in the set of mount points on proc and sysfs that are created specially. This set of changes also starts enforcing the mount flags of fresh mounts of proc and sysfs are consistent with the existing mount of proc and sysfs. I expected this to be the boring part of the work but unfortunately unprivileged userspace winds up mounting fresh copies of proc and sysfs with noexec and nosuid clear when root set those flags on the previous mount of proc and sysfs. So for now only the atime, read-only and nodev attributes which userspace happens to keep consistent are enforced. Dealing with the noexec and nosuid attributes remains for another time. This set of changes also addresses an issue with how open file descriptors from /proc/<pid>/ns/* are displayed. Recently readlink of /proc/<pid>/fd has been triggering a WARN_ON that has not been meaningful since it was added (as all of the code in the kernel was converted) and is not now actively wrong. There is also a short list of issues that have not been fixed yet that I will mention briefly. It is possible to rename a directory from below to above a bind mount. At which point any directory pointers below the renamed directory can be walked up to the root directory of the filesystem. With user namespaces enabled a bind mount of the bind mount can be created allowing the user to pick a directory whose children they can rename to outside of the bind mount. This is challenging to fix and doubly so because all obvious solutions must touch code that is in the performance part of pathname resolution. As mentioned above there is also a question of how to ensure that developers by accident or with purpose do not introduce exectuable files on sysfs and proc and in doing so introduce security regressions in the current userspace that will not be immediately obvious and as such are likely to require breaking userspace in painful ways once they are recognized" * 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace: vfs: Remove incorrect debugging WARN in prepend_path mnt: Update fs_fully_visible to test for permanently empty directories sysfs: Create mountpoints with sysfs_create_mount_point sysfs: Add support for permanently empty directories to serve as mount points. kernfs: Add support for always empty directories. proc: Allow creating permanently empty directories that serve as mount points sysctl: Allow creating permanently empty directories that serve as mountpoints. fs: Add helper functions for permanently empty directories. vfs: Ignore unlocked mounts in fs_fully_visible mnt: Modify fs_fully_visible to deal with locked ro nodev and atime mnt: Refactor the logic for mounting sysfs and proc in a user namespace
Diffstat (limited to 'fs/proc')
-rw-r--r--fs/proc/generic.c23
-rw-r--r--fs/proc/inode.c4
-rw-r--r--fs/proc/internal.h6
-rw-r--r--fs/proc/proc_sysctl.c37
-rw-r--r--fs/proc/root.c9
5 files changed, 73 insertions, 6 deletions
diff --git a/fs/proc/generic.c b/fs/proc/generic.c
index df6327a2b865..e5dee5c3188e 100644
--- a/fs/proc/generic.c
+++ b/fs/proc/generic.c
@@ -373,6 +373,10 @@ static struct proc_dir_entry *__proc_create(struct proc_dir_entry **parent,
WARN(1, "create '/proc/%s' by hand\n", qstr.name);
return NULL;
}
+ if (is_empty_pde(*parent)) {
+ WARN(1, "attempt to add to permanently empty directory");
+ return NULL;
+ }
ent = kzalloc(sizeof(struct proc_dir_entry) + qstr.len + 1, GFP_KERNEL);
if (!ent)
@@ -455,6 +459,25 @@ struct proc_dir_entry *proc_mkdir(const char *name,
}
EXPORT_SYMBOL(proc_mkdir);
+struct proc_dir_entry *proc_create_mount_point(const char *name)
+{
+ umode_t mode = S_IFDIR | S_IRUGO | S_IXUGO;
+ struct proc_dir_entry *ent, *parent = NULL;
+
+ ent = __proc_create(&parent, name, mode, 2);
+ if (ent) {
+ ent->data = NULL;
+ ent->proc_fops = NULL;
+ ent->proc_iops = NULL;
+ if (proc_register(parent, ent) < 0) {
+ kfree(ent);
+ parent->nlink--;
+ ent = NULL;
+ }
+ }
+ return ent;
+}
+
struct proc_dir_entry *proc_create_data(const char *name, umode_t mode,
struct proc_dir_entry *parent,
const struct file_operations *proc_fops,
diff --git a/fs/proc/inode.c b/fs/proc/inode.c
index afe232b9df6e..bd95b9fdebb0 100644
--- a/fs/proc/inode.c
+++ b/fs/proc/inode.c
@@ -422,6 +422,10 @@ struct inode *proc_get_inode(struct super_block *sb, struct proc_dir_entry *de)
inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
PROC_I(inode)->pde = de;
+ if (is_empty_pde(de)) {
+ make_empty_dir_inode(inode);
+ return inode;
+ }
if (de->mode) {
inode->i_mode = de->mode;
inode->i_uid = de->uid;
diff --git a/fs/proc/internal.h b/fs/proc/internal.h
index c835b94c0cd3..aa2781095bd1 100644
--- a/fs/proc/internal.h
+++ b/fs/proc/internal.h
@@ -191,6 +191,12 @@ static inline struct proc_dir_entry *pde_get(struct proc_dir_entry *pde)
}
extern void pde_put(struct proc_dir_entry *);
+static inline bool is_empty_pde(const struct proc_dir_entry *pde)
+{
+ return S_ISDIR(pde->mode) && !pde->proc_iops;
+}
+struct proc_dir_entry *proc_create_mount_point(const char *name);
+
/*
* inode.c
*/
diff --git a/fs/proc/proc_sysctl.c b/fs/proc/proc_sysctl.c
index fea2561d773b..fdda62e6115e 100644
--- a/fs/proc/proc_sysctl.c
+++ b/fs/proc/proc_sysctl.c
@@ -19,6 +19,28 @@ static const struct inode_operations proc_sys_inode_operations;
static const struct file_operations proc_sys_dir_file_operations;
static const struct inode_operations proc_sys_dir_operations;
+/* Support for permanently empty directories */
+
+struct ctl_table sysctl_mount_point[] = {
+ { }
+};
+
+static bool is_empty_dir(struct ctl_table_header *head)
+{
+ return head->ctl_table[0].child == sysctl_mount_point;
+}
+
+static void set_empty_dir(struct ctl_dir *dir)
+{
+ dir->header.ctl_table[0].child = sysctl_mount_point;
+}
+
+static void clear_empty_dir(struct ctl_dir *dir)
+
+{
+ dir->header.ctl_table[0].child = NULL;
+}
+
void proc_sys_poll_notify(struct ctl_table_poll *poll)
{
if (!poll)
@@ -187,6 +209,17 @@ static int insert_header(struct ctl_dir *dir, struct ctl_table_header *header)
struct ctl_table *entry;
int err;
+ /* Is this a permanently empty directory? */
+ if (is_empty_dir(&dir->header))
+ return -EROFS;
+
+ /* Am I creating a permanently empty directory? */
+ if (header->ctl_table == sysctl_mount_point) {
+ if (!RB_EMPTY_ROOT(&dir->root))
+ return -EINVAL;
+ set_empty_dir(dir);
+ }
+
dir->header.nreg++;
header->parent = dir;
err = insert_links(header);
@@ -202,6 +235,8 @@ fail:
erase_header(header);
put_links(header);
fail_links:
+ if (header->ctl_table == sysctl_mount_point)
+ clear_empty_dir(dir);
header->parent = NULL;
drop_sysctl_table(&dir->header);
return err;
@@ -419,6 +454,8 @@ static struct inode *proc_sys_make_inode(struct super_block *sb,
inode->i_mode |= S_IFDIR;
inode->i_op = &proc_sys_dir_operations;
inode->i_fop = &proc_sys_dir_file_operations;
+ if (is_empty_dir(head))
+ make_empty_dir_inode(inode);
}
out:
return inode;
diff --git a/fs/proc/root.c b/fs/proc/root.c
index b7fa4bfe896a..68feb0f70e63 100644
--- a/fs/proc/root.c
+++ b/fs/proc/root.c
@@ -112,9 +112,6 @@ static struct dentry *proc_mount(struct file_system_type *fs_type,
ns = task_active_pid_ns(current);
options = data;
- if (!capable(CAP_SYS_ADMIN) && !fs_fully_visible(fs_type))
- return ERR_PTR(-EPERM);
-
/* Does the mounter have privilege over the pid namespace? */
if (!ns_capable(ns->user_ns, CAP_SYS_ADMIN))
return ERR_PTR(-EPERM);
@@ -159,7 +156,7 @@ static struct file_system_type proc_fs_type = {
.name = "proc",
.mount = proc_mount,
.kill_sb = proc_kill_sb,
- .fs_flags = FS_USERNS_MOUNT,
+ .fs_flags = FS_USERNS_VISIBLE | FS_USERNS_MOUNT,
};
void __init proc_root_init(void)
@@ -182,10 +179,10 @@ void __init proc_root_init(void)
#endif
proc_mkdir("fs", NULL);
proc_mkdir("driver", NULL);
- proc_mkdir("fs/nfsd", NULL); /* somewhere for the nfsd filesystem to be mounted */
+ proc_create_mount_point("fs/nfsd"); /* somewhere for the nfsd filesystem to be mounted */
#if defined(CONFIG_SUN_OPENPROMFS) || defined(CONFIG_SUN_OPENPROMFS_MODULE)
/* just give it a mountpoint */
- proc_mkdir("openprom", NULL);
+ proc_create_mount_point("openprom");
#endif
proc_tty_init();
proc_mkdir("bus", NULL);