[PATCH 11/43] convert do_remount_sb() to fs_context
David Howells
dhowells at redhat.com
Tue Feb 19 16:29:54 UTC 2019
Replace do_remount_sb() with a function, reconfigure_super(), that's
fs_context aware. The fs_context is expected to be parameterised already
and have ->root pointing to the superblock to be reconfigured.
A legacy wrapper is provided that is intended to be called from the
fs_context ops when those appear, but for now is called directly from
reconfigure_super(). This wrapper invokes the ->remount_fs() superblock op
for the moment. It is intended that the remount_fs() op will be phased
out.
The fs_context->purpose is set to FS_CONTEXT_FOR_RECONFIGURE to indicate
that the context is being used for reconfiguration.
do_umount_root() is provided to consolidate remount-to-R/O for umount and
emergency remount by creating a context and invoking reconfiguration.
do_remount(), do_umount() and do_emergency_remount_callback() are switched
to use the new process.
[AV -- fold UMOUNT and EMERGENCY_REMOUNT in; fixes the
umount / bug, gets rid of pointless complexity]
[AV -- set ->net_ns in all cases; nfs remount will need that]
[AV -- shift security_sb_remount() call into reconfigure_super(); the callers
that didn't do security_sb_remount() have NULL fc->security anyway, so it's
a no-op for them]
Signed-off-by: David Howells <dhowells at redhat.com>
Co-developed-by: Al Viro <viro at zeniv.linux.org.uk>
Signed-off-by: Al Viro <viro at zeniv.linux.org.uk>
---
fs/fs_context.c | 35 ++++++++++++++
fs/internal.h | 3 +
fs/namespace.c | 61 ++++++++++++++++---------
fs/super.c | 107 ++++++++++++++++++++++++++++++--------------
include/linux/fs.h | 1
include/linux/fs_context.h | 4 ++
6 files changed, 152 insertions(+), 59 deletions(-)
diff --git a/fs/fs_context.c b/fs/fs_context.c
index 857cd46a687b..5e2c3aba1dd8 100644
--- a/fs/fs_context.c
+++ b/fs/fs_context.c
@@ -69,6 +69,13 @@ static struct fs_context *alloc_fs_context(struct file_system_type *fs_type,
case FS_CONTEXT_FOR_MOUNT:
fc->user_ns = get_user_ns(fc->cred->user_ns);
break;
+ case FS_CONTEXT_FOR_RECONFIGURE:
+ /* We don't pin any namespaces as the superblock's
+ * subscriptions cannot be changed at this point.
+ */
+ atomic_inc(&reference->d_sb->s_active);
+ fc->root = dget(reference);
+ break;
}
ret = legacy_init_fs_context(fc);
@@ -90,6 +97,15 @@ struct fs_context *fs_context_for_mount(struct file_system_type *fs_type,
}
EXPORT_SYMBOL(fs_context_for_mount);
+struct fs_context *fs_context_for_reconfigure(struct dentry *dentry,
+ unsigned int sb_flags,
+ unsigned int sb_flags_mask)
+{
+ return alloc_fs_context(dentry->d_sb->s_type, dentry, sb_flags,
+ sb_flags_mask, FS_CONTEXT_FOR_RECONFIGURE);
+}
+EXPORT_SYMBOL(fs_context_for_reconfigure);
+
void fc_drop_locked(struct fs_context *fc)
{
struct super_block *sb = fc->root->d_sb;
@@ -99,6 +115,7 @@ void fc_drop_locked(struct fs_context *fc)
}
static void legacy_fs_context_free(struct fs_context *fc);
+
/**
* put_fs_context - Dispose of a superblock configuration context.
* @fc: The context to dispose of.
@@ -118,8 +135,7 @@ void put_fs_context(struct fs_context *fc)
legacy_fs_context_free(fc);
security_free_mnt_opts(&fc->security);
- if (fc->net_ns)
- put_net(fc->net_ns);
+ put_net(fc->net_ns);
put_user_ns(fc->user_ns);
put_cred(fc->cred);
kfree(fc->subtype);
@@ -172,6 +188,21 @@ int legacy_get_tree(struct fs_context *fc)
return 0;
}
+/*
+ * Handle remount.
+ */
+int legacy_reconfigure(struct fs_context *fc)
+{
+ struct legacy_fs_context *ctx = fc->fs_private;
+ struct super_block *sb = fc->root->d_sb;
+
+ if (!sb->s_op->remount_fs)
+ return 0;
+
+ return sb->s_op->remount_fs(sb, &fc->sb_flags,
+ ctx ? ctx->legacy_data : NULL);
+}
+
/*
* Initialise a legacy context for a filesystem that doesn't support
* fs_context.
diff --git a/fs/internal.h b/fs/internal.h
index 6af26d897034..016a5b8dd305 100644
--- a/fs/internal.h
+++ b/fs/internal.h
@@ -56,6 +56,7 @@ extern void __init chrdev_init(void);
* fs_context.c
*/
extern int legacy_get_tree(struct fs_context *fc);
+extern int legacy_reconfigure(struct fs_context *fc);
extern int parse_monolithic_mount_data(struct fs_context *, void *);
extern void fc_drop_locked(struct fs_context *);
@@ -107,7 +108,7 @@ extern struct file *alloc_empty_file_noaccount(int, const struct cred *);
/*
* super.c
*/
-extern int do_remount_sb(struct super_block *, int, void *, int);
+extern int reconfigure_super(struct fs_context *);
extern bool trylock_super(struct super_block *sb);
extern struct super_block *user_get_super(dev_t);
diff --git a/fs/namespace.c b/fs/namespace.c
index 750500c6c33d..931228d8518a 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -1489,6 +1489,29 @@ static void umount_tree(struct mount *mnt, enum umount_tree_flags how)
static void shrink_submounts(struct mount *mnt);
+static int do_umount_root(struct super_block *sb)
+{
+ int ret = 0;
+
+ down_write(&sb->s_umount);
+ if (!sb_rdonly(sb)) {
+ struct fs_context *fc;
+
+ fc = fs_context_for_reconfigure(sb->s_root, SB_RDONLY,
+ SB_RDONLY);
+ if (IS_ERR(fc)) {
+ ret = PTR_ERR(fc);
+ } else {
+ ret = parse_monolithic_mount_data(fc, NULL);
+ if (!ret)
+ ret = reconfigure_super(fc);
+ put_fs_context(fc);
+ }
+ }
+ up_write(&sb->s_umount);
+ return ret;
+}
+
static int do_umount(struct mount *mnt, int flags)
{
struct super_block *sb = mnt->mnt.mnt_sb;
@@ -1554,11 +1577,7 @@ static int do_umount(struct mount *mnt, int flags)
*/
if (!ns_capable(sb->s_user_ns, CAP_SYS_ADMIN))
return -EPERM;
- down_write(&sb->s_umount);
- if (!sb_rdonly(sb))
- retval = do_remount_sb(sb, SB_RDONLY, NULL, 0);
- up_write(&sb->s_umount);
- return retval;
+ return do_umount_root(sb);
}
namespace_lock();
@@ -2367,7 +2386,7 @@ static int do_remount(struct path *path, int ms_flags, int sb_flags,
int err;
struct super_block *sb = path->mnt->mnt_sb;
struct mount *mnt = real_mount(path->mnt);
- void *sec_opts = NULL;
+ struct fs_context *fc;
if (!check_mnt(mnt))
return -EINVAL;
@@ -2378,24 +2397,22 @@ static int do_remount(struct path *path, int ms_flags, int sb_flags,
if (!can_change_locked_flags(mnt, mnt_flags))
return -EPERM;
- if (data && !(sb->s_type->fs_flags & FS_BINARY_MOUNTDATA)) {
- err = security_sb_eat_lsm_opts(data, &sec_opts);
- if (err)
- return err;
- }
- err = security_sb_remount(sb, sec_opts);
- security_free_mnt_opts(&sec_opts);
- if (err)
- return err;
+ fc = fs_context_for_reconfigure(path->dentry, sb_flags, MS_RMT_MASK);
+ if (IS_ERR(fc))
+ return PTR_ERR(fc);
- down_write(&sb->s_umount);
- err = -EPERM;
- if (ns_capable(sb->s_user_ns, CAP_SYS_ADMIN)) {
- err = do_remount_sb(sb, sb_flags, data, 0);
- if (!err)
- set_mount_attributes(mnt, mnt_flags);
+ err = parse_monolithic_mount_data(fc, data);
+ if (!err) {
+ down_write(&sb->s_umount);
+ err = -EPERM;
+ if (ns_capable(sb->s_user_ns, CAP_SYS_ADMIN)) {
+ err = reconfigure_super(fc);
+ if (!err)
+ set_mount_attributes(mnt, mnt_flags);
+ }
+ up_write(&sb->s_umount);
}
- up_write(&sb->s_umount);
+ put_fs_context(fc);
return err;
}
diff --git a/fs/super.c b/fs/super.c
index 11e2a6cb3baf..50553233dd15 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -836,28 +836,35 @@ struct super_block *user_get_super(dev_t dev)
}
/**
- * do_remount_sb - asks filesystem to change mount options.
- * @sb: superblock in question
- * @sb_flags: revised superblock flags
- * @data: the rest of options
- * @force: whether or not to force the change
+ * reconfigure_super - asks filesystem to change superblock parameters
+ * @fc: The superblock and configuration
*
- * Alters the mount options of a mounted file system.
+ * Alters the configuration parameters of a live superblock.
*/
-int do_remount_sb(struct super_block *sb, int sb_flags, void *data, int force)
+int reconfigure_super(struct fs_context *fc)
{
+ struct super_block *sb = fc->root->d_sb;
int retval;
- int remount_ro;
+ bool remount_ro = false;
+ bool force = fc->sb_flags & SB_FORCE;
+ if (fc->sb_flags_mask & ~MS_RMT_MASK)
+ return -EINVAL;
if (sb->s_writers.frozen != SB_UNFROZEN)
return -EBUSY;
+ retval = security_sb_remount(sb, fc->security);
+ if (retval)
+ return retval;
+
+ if (fc->sb_flags_mask & SB_RDONLY) {
#ifdef CONFIG_BLOCK
- if (!(sb_flags & SB_RDONLY) && bdev_read_only(sb->s_bdev))
- return -EACCES;
+ if (!(fc->sb_flags & SB_RDONLY) && bdev_read_only(sb->s_bdev))
+ return -EACCES;
#endif
- remount_ro = (sb_flags & SB_RDONLY) && !sb_rdonly(sb);
+ remount_ro = (fc->sb_flags & SB_RDONLY) && !sb_rdonly(sb);
+ }
if (remount_ro) {
if (!hlist_empty(&sb->s_pins)) {
@@ -868,13 +875,14 @@ int do_remount_sb(struct super_block *sb, int sb_flags, void *data, int force)
return 0;
if (sb->s_writers.frozen != SB_UNFROZEN)
return -EBUSY;
- remount_ro = (sb_flags & SB_RDONLY) && !sb_rdonly(sb);
+ remount_ro = !sb_rdonly(sb);
}
}
shrink_dcache_sb(sb);
- /* If we are remounting RDONLY and current sb is read/write,
- make sure there are no rw files opened */
+ /* If we are reconfiguring to RDONLY and current sb is read/write,
+ * make sure there are no files open for writing.
+ */
if (remount_ro) {
if (force) {
sb->s_readonly_remount = 1;
@@ -886,17 +894,17 @@ int do_remount_sb(struct super_block *sb, int sb_flags, void *data, int force)
}
}
- if (sb->s_op->remount_fs) {
- retval = sb->s_op->remount_fs(sb, &sb_flags, data);
- if (retval) {
- if (!force)
- goto cancel_readonly;
- /* If forced remount, go ahead despite any errors */
- WARN(1, "forced remount of a %s fs returned %i\n",
- sb->s_type->name, retval);
- }
+ retval = legacy_reconfigure(fc);
+ if (retval) {
+ if (!force)
+ goto cancel_readonly;
+ /* If forced remount, go ahead despite any errors */
+ WARN(1, "forced remount of a %s fs returned %i\n",
+ sb->s_type->name, retval);
}
- sb->s_flags = (sb->s_flags & ~MS_RMT_MASK) | (sb_flags & MS_RMT_MASK);
+
+ WRITE_ONCE(sb->s_flags, ((sb->s_flags & ~fc->sb_flags_mask) |
+ (fc->sb_flags & fc->sb_flags_mask)));
/* Needs to be ordered wrt mnt_is_readonly() */
smp_wmb();
sb->s_readonly_remount = 0;
@@ -923,10 +931,15 @@ static void do_emergency_remount_callback(struct super_block *sb)
down_write(&sb->s_umount);
if (sb->s_root && sb->s_bdev && (sb->s_flags & SB_BORN) &&
!sb_rdonly(sb)) {
- /*
- * What lock protects sb->s_flags??
- */
- do_remount_sb(sb, SB_RDONLY, NULL, 1);
+ struct fs_context *fc;
+
+ fc = fs_context_for_reconfigure(sb->s_root,
+ SB_RDONLY | SB_FORCE, SB_RDONLY);
+ if (!IS_ERR(fc)) {
+ if (parse_monolithic_mount_data(fc, NULL) == 0)
+ (void)reconfigure_super(fc);
+ put_fs_context(fc);
+ }
}
up_write(&sb->s_umount);
}
@@ -1213,6 +1226,31 @@ struct dentry *mount_nodev(struct file_system_type *fs_type,
}
EXPORT_SYMBOL(mount_nodev);
+static int reconfigure_single(struct super_block *s,
+ int flags, void *data)
+{
+ struct fs_context *fc;
+ int ret;
+
+ /* The caller really need to be passing fc down into mount_single(),
+ * then a chunk of this can be removed. [Bollocks -- AV]
+ * Better yet, reconfiguration shouldn't happen, but rather the second
+ * mount should be rejected if the parameters are not compatible.
+ */
+ fc = fs_context_for_reconfigure(s->s_root, flags, MS_RMT_MASK);
+ if (IS_ERR(fc))
+ return PTR_ERR(fc);
+
+ ret = parse_monolithic_mount_data(fc, data);
+ if (ret < 0)
+ goto out;
+
+ ret = reconfigure_super(fc);
+out:
+ put_fs_context(fc);
+ return ret;
+}
+
static int compare_single(struct super_block *s, void *p)
{
return 1;
@@ -1230,13 +1268,14 @@ struct dentry *mount_single(struct file_system_type *fs_type,
return ERR_CAST(s);
if (!s->s_root) {
error = fill_super(s, data, flags & SB_SILENT ? 1 : 0);
- if (error) {
- deactivate_locked_super(s);
- return ERR_PTR(error);
- }
- s->s_flags |= SB_ACTIVE;
+ if (!error)
+ s->s_flags |= SB_ACTIVE;
} else {
- do_remount_sb(s, flags, data, 0);
+ error = reconfigure_single(s, flags, data);
+ }
+ if (unlikely(error)) {
+ deactivate_locked_super(s);
+ return ERR_PTR(error);
}
return dget(s->s_root);
}
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 36fff12ab890..c65d02c5c512 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1337,6 +1337,7 @@ extern int send_sigurg(struct fown_struct *fown);
/* These sb flags are internal to the kernel */
#define SB_SUBMOUNT (1<<26)
+#define SB_FORCE (1<<27)
#define SB_NOSEC (1<<28)
#define SB_BORN (1<<29)
#define SB_ACTIVE (1<<30)
diff --git a/include/linux/fs_context.h b/include/linux/fs_context.h
index 9805514444c9..98772f882a3e 100644
--- a/include/linux/fs_context.h
+++ b/include/linux/fs_context.h
@@ -25,6 +25,7 @@ struct user_namespace;
enum fs_context_purpose {
FS_CONTEXT_FOR_MOUNT, /* New superblock for explicit mount */
+ FS_CONTEXT_FOR_RECONFIGURE, /* Superblock reconfiguration (remount) */
};
/*
@@ -57,6 +58,9 @@ struct fs_context {
*/
extern struct fs_context *fs_context_for_mount(struct file_system_type *fs_type,
unsigned int sb_flags);
+extern struct fs_context *fs_context_for_reconfigure(struct dentry *dentry,
+ unsigned int sb_flags,
+ unsigned int sb_flags_mask);
extern int vfs_get_tree(struct fs_context *fc);
extern void put_fs_context(struct fs_context *fc);
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