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-rw-r--r--fs/namespace.c316
1 files changed, 314 insertions, 2 deletions
diff --git a/fs/namespace.c b/fs/namespace.c
index 94f026ec990a..678f7ce060f2 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -17,6 +17,7 @@
#include <linux/quotaops.h>
#include <linux/acct.h>
#include <linux/capability.h>
+#include <linux/cpumask.h>
#include <linux/module.h>
#include <linux/sysfs.h>
#include <linux/seq_file.h>
@@ -55,6 +56,8 @@ static inline unsigned long hash(struct vfsmount *mnt, struct dentry *dentry)
return tmp & (HASH_SIZE - 1);
}
+#define MNT_WRITER_UNDERFLOW_LIMIT -(1<<16)
+
struct vfsmount *alloc_vfsmnt(const char *name)
{
struct vfsmount *mnt = kmem_cache_zalloc(mnt_cache, GFP_KERNEL);
@@ -68,6 +71,7 @@ struct vfsmount *alloc_vfsmnt(const char *name)
INIT_LIST_HEAD(&mnt->mnt_share);
INIT_LIST_HEAD(&mnt->mnt_slave_list);
INIT_LIST_HEAD(&mnt->mnt_slave);
+ atomic_set(&mnt->__mnt_writers, 0);
if (name) {
int size = strlen(name) + 1;
char *newname = kmalloc(size, GFP_KERNEL);
@@ -80,6 +84,263 @@ struct vfsmount *alloc_vfsmnt(const char *name)
return mnt;
}
+/*
+ * Most r/o checks on a fs are for operations that take
+ * discrete amounts of time, like a write() or unlink().
+ * We must keep track of when those operations start
+ * (for permission checks) and when they end, so that
+ * we can determine when writes are able to occur to
+ * a filesystem.
+ */
+/*
+ * __mnt_is_readonly: check whether a mount is read-only
+ * @mnt: the mount to check for its write status
+ *
+ * This shouldn't be used directly ouside of the VFS.
+ * It does not guarantee that the filesystem will stay
+ * r/w, just that it is right *now*. This can not and
+ * should not be used in place of IS_RDONLY(inode).
+ * mnt_want/drop_write() will _keep_ the filesystem
+ * r/w.
+ */
+int __mnt_is_readonly(struct vfsmount *mnt)
+{
+ if (mnt->mnt_flags & MNT_READONLY)
+ return 1;
+ if (mnt->mnt_sb->s_flags & MS_RDONLY)
+ return 1;
+ return 0;
+}
+EXPORT_SYMBOL_GPL(__mnt_is_readonly);
+
+struct mnt_writer {
+ /*
+ * If holding multiple instances of this lock, they
+ * must be ordered by cpu number.
+ */
+ spinlock_t lock;
+ struct lock_class_key lock_class; /* compiles out with !lockdep */
+ unsigned long count;
+ struct vfsmount *mnt;
+} ____cacheline_aligned_in_smp;
+static DEFINE_PER_CPU(struct mnt_writer, mnt_writers);
+
+static int __init init_mnt_writers(void)
+{
+ int cpu;
+ for_each_possible_cpu(cpu) {
+ struct mnt_writer *writer = &per_cpu(mnt_writers, cpu);
+ spin_lock_init(&writer->lock);
+ lockdep_set_class(&writer->lock, &writer->lock_class);
+ writer->count = 0;
+ }
+ return 0;
+}
+fs_initcall(init_mnt_writers);
+
+static void unlock_mnt_writers(void)
+{
+ int cpu;
+ struct mnt_writer *cpu_writer;
+
+ for_each_possible_cpu(cpu) {
+ cpu_writer = &per_cpu(mnt_writers, cpu);
+ spin_unlock(&cpu_writer->lock);
+ }
+}
+
+static inline void __clear_mnt_count(struct mnt_writer *cpu_writer)
+{
+ if (!cpu_writer->mnt)
+ return;
+ /*
+ * This is in case anyone ever leaves an invalid,
+ * old ->mnt and a count of 0.
+ */
+ if (!cpu_writer->count)
+ return;
+ atomic_add(cpu_writer->count, &cpu_writer->mnt->__mnt_writers);
+ cpu_writer->count = 0;
+}
+ /*
+ * must hold cpu_writer->lock
+ */
+static inline void use_cpu_writer_for_mount(struct mnt_writer *cpu_writer,
+ struct vfsmount *mnt)
+{
+ if (cpu_writer->mnt == mnt)
+ return;
+ __clear_mnt_count(cpu_writer);
+ cpu_writer->mnt = mnt;
+}
+
+/*
+ * Most r/o checks on a fs are for operations that take
+ * discrete amounts of time, like a write() or unlink().
+ * We must keep track of when those operations start
+ * (for permission checks) and when they end, so that
+ * we can determine when writes are able to occur to
+ * a filesystem.
+ */
+/**
+ * mnt_want_write - get write access to a mount
+ * @mnt: the mount on which to take a write
+ *
+ * This tells the low-level filesystem that a write is
+ * about to be performed to it, and makes sure that
+ * writes are allowed before returning success. When
+ * the write operation is finished, mnt_drop_write()
+ * must be called. This is effectively a refcount.
+ */
+int mnt_want_write(struct vfsmount *mnt)
+{
+ int ret = 0;
+ struct mnt_writer *cpu_writer;
+
+ cpu_writer = &get_cpu_var(mnt_writers);
+ spin_lock(&cpu_writer->lock);
+ if (__mnt_is_readonly(mnt)) {
+ ret = -EROFS;
+ goto out;
+ }
+ use_cpu_writer_for_mount(cpu_writer, mnt);
+ cpu_writer->count++;
+out:
+ spin_unlock(&cpu_writer->lock);
+ put_cpu_var(mnt_writers);
+ return ret;
+}
+EXPORT_SYMBOL_GPL(mnt_want_write);
+
+static void lock_mnt_writers(void)
+{
+ int cpu;
+ struct mnt_writer *cpu_writer;
+
+ for_each_possible_cpu(cpu) {
+ cpu_writer = &per_cpu(mnt_writers, cpu);
+ spin_lock(&cpu_writer->lock);
+ __clear_mnt_count(cpu_writer);
+ cpu_writer->mnt = NULL;
+ }
+}
+
+/*
+ * These per-cpu write counts are not guaranteed to have
+ * matched increments and decrements on any given cpu.
+ * A file open()ed for write on one cpu and close()d on
+ * another cpu will imbalance this count. Make sure it
+ * does not get too far out of whack.
+ */
+static void handle_write_count_underflow(struct vfsmount *mnt)
+{
+ if (atomic_read(&mnt->__mnt_writers) >=
+ MNT_WRITER_UNDERFLOW_LIMIT)
+ return;
+ /*
+ * It isn't necessary to hold all of the locks
+ * at the same time, but doing it this way makes
+ * us share a lot more code.
+ */
+ lock_mnt_writers();
+ /*
+ * vfsmount_lock is for mnt_flags.
+ */
+ spin_lock(&vfsmount_lock);
+ /*
+ * If coalescing the per-cpu writer counts did not
+ * get us back to a positive writer count, we have
+ * a bug.
+ */
+ if ((atomic_read(&mnt->__mnt_writers) < 0) &&
+ !(mnt->mnt_flags & MNT_IMBALANCED_WRITE_COUNT)) {
+ printk(KERN_DEBUG "leak detected on mount(%p) writers "
+ "count: %d\n",
+ mnt, atomic_read(&mnt->__mnt_writers));
+ WARN_ON(1);
+ /* use the flag to keep the dmesg spam down */
+ mnt->mnt_flags |= MNT_IMBALANCED_WRITE_COUNT;
+ }
+ spin_unlock(&vfsmount_lock);
+ unlock_mnt_writers();
+}
+
+/**
+ * mnt_drop_write - give up write access to a mount
+ * @mnt: the mount on which to give up write access
+ *
+ * Tells the low-level filesystem that we are done
+ * performing writes to it. Must be matched with
+ * mnt_want_write() call above.
+ */
+void mnt_drop_write(struct vfsmount *mnt)
+{
+ int must_check_underflow = 0;
+ struct mnt_writer *cpu_writer;
+
+ cpu_writer = &get_cpu_var(mnt_writers);
+ spin_lock(&cpu_writer->lock);
+
+ use_cpu_writer_for_mount(cpu_writer, mnt);
+ if (cpu_writer->count > 0) {
+ cpu_writer->count--;
+ } else {
+ must_check_underflow = 1;
+ atomic_dec(&mnt->__mnt_writers);
+ }
+
+ spin_unlock(&cpu_writer->lock);
+ /*
+ * Logically, we could call this each time,
+ * but the __mnt_writers cacheline tends to
+ * be cold, and makes this expensive.
+ */
+ if (must_check_underflow)
+ handle_write_count_underflow(mnt);
+ /*
+ * This could be done right after the spinlock
+ * is taken because the spinlock keeps us on
+ * the cpu, and disables preemption. However,
+ * putting it here bounds the amount that
+ * __mnt_writers can underflow. Without it,
+ * we could theoretically wrap __mnt_writers.
+ */
+ put_cpu_var(mnt_writers);
+}
+EXPORT_SYMBOL_GPL(mnt_drop_write);
+
+static int mnt_make_readonly(struct vfsmount *mnt)
+{
+ int ret = 0;
+
+ lock_mnt_writers();
+ /*
+ * With all the locks held, this value is stable
+ */
+ if (atomic_read(&mnt->__mnt_writers) > 0) {
+ ret = -EBUSY;
+ goto out;
+ }
+ /*
+ * nobody can do a successful mnt_want_write() with all
+ * of the counts in MNT_DENIED_WRITE and the locks held.
+ */
+ spin_lock(&vfsmount_lock);
+ if (!ret)
+ mnt->mnt_flags |= MNT_READONLY;
+ spin_unlock(&vfsmount_lock);
+out:
+ unlock_mnt_writers();
+ return ret;
+}
+
+static void __mnt_unmake_readonly(struct vfsmount *mnt)
+{
+ spin_lock(&vfsmount_lock);
+ mnt->mnt_flags &= ~MNT_READONLY;
+ spin_unlock(&vfsmount_lock);
+}
+
int simple_set_mnt(struct vfsmount *mnt, struct super_block *sb)
{
mnt->mnt_sb = sb;
@@ -271,7 +532,36 @@ static struct vfsmount *clone_mnt(struct vfsmount *old, struct dentry *root,
static inline void __mntput(struct vfsmount *mnt)
{
+ int cpu;
struct super_block *sb = mnt->mnt_sb;
+ /*
+ * We don't have to hold all of the locks at the
+ * same time here because we know that we're the
+ * last reference to mnt and that no new writers
+ * can come in.
+ */
+ for_each_possible_cpu(cpu) {
+ struct mnt_writer *cpu_writer = &per_cpu(mnt_writers, cpu);
+ if (cpu_writer->mnt != mnt)
+ continue;
+ spin_lock(&cpu_writer->lock);
+ atomic_add(cpu_writer->count, &mnt->__mnt_writers);
+ cpu_writer->count = 0;
+ /*
+ * Might as well do this so that no one
+ * ever sees the pointer and expects
+ * it to be valid.
+ */
+ cpu_writer->mnt = NULL;
+ spin_unlock(&cpu_writer->lock);
+ }
+ /*
+ * This probably indicates that somebody messed
+ * up a mnt_want/drop_write() pair. If this
+ * happens, the filesystem was probably unable
+ * to make r/w->r/o transitions.
+ */
+ WARN_ON(atomic_read(&mnt->__mnt_writers));
dput(mnt->mnt_root);
free_vfsmnt(mnt);
deactivate_super(sb);
@@ -417,7 +707,7 @@ static int show_vfsmnt(struct seq_file *m, void *v)
seq_putc(m, '.');
mangle(m, mnt->mnt_sb->s_subtype);
}
- seq_puts(m, mnt->mnt_sb->s_flags & MS_RDONLY ? " ro" : " rw");
+ seq_puts(m, __mnt_is_readonly(mnt) ? " ro" : " rw");
for (fs_infop = fs_info; fs_infop->flag; fs_infop++) {
if (mnt->mnt_sb->s_flags & fs_infop->flag)
seq_puts(m, fs_infop->str);
@@ -1019,6 +1309,23 @@ out:
return err;
}
+static int change_mount_flags(struct vfsmount *mnt, int ms_flags)
+{
+ int error = 0;
+ int readonly_request = 0;
+
+ if (ms_flags & MS_RDONLY)
+ readonly_request = 1;
+ if (readonly_request == __mnt_is_readonly(mnt))
+ return 0;
+
+ if (readonly_request)
+ error = mnt_make_readonly(mnt);
+ else
+ __mnt_unmake_readonly(mnt);
+ return error;
+}
+
/*
* change filesystem flags. dir should be a physical root of filesystem.
* If you've mounted a non-root directory somewhere and want to do remount
@@ -1041,7 +1348,10 @@ static noinline int do_remount(struct nameidata *nd, int flags, int mnt_flags,
return -EINVAL;
down_write(&sb->s_umount);
- err = do_remount_sb(sb, flags, data, 0);
+ if (flags & MS_BIND)
+ err = change_mount_flags(nd->path.mnt, flags);
+ else
+ err = do_remount_sb(sb, flags, data, 0);
if (!err)
nd->path.mnt->mnt_flags = mnt_flags;
up_write(&sb->s_umount);
@@ -1425,6 +1735,8 @@ long do_mount(char *dev_name, char *dir_name, char *type_page,
mnt_flags |= MNT_NODIRATIME;
if (flags & MS_RELATIME)
mnt_flags |= MNT_RELATIME;
+ if (flags & MS_RDONLY)
+ mnt_flags |= MNT_READONLY;
flags &= ~(MS_NOSUID | MS_NOEXEC | MS_NODEV | MS_ACTIVE |
MS_NOATIME | MS_NODIRATIME | MS_RELATIME| MS_KERNMOUNT);