[PATCH] Restore task fs_root and pwd (v2)
Oren Laadan
orenl at cs.columbia.edu
Wed Jan 20 12:28:13 PST 2010
Very necessary !
See comments inline.
Serge E. Hallyn wrote:
> Checkpoint and restore task->fs. Tasks sharing task->fs will
> share them again after restart.
>
> Changelog:
> Dec 28: Addressed comments by Oren (and Dave)
> 1. define and use {get,put}_fs_struct helpers
> 2. fix locking comment
> 3. define ckpt_read_fname() and use in checkpoint/files.c
>
> Signed-off-by: Serge E. Hallyn <serue at us.ibm.com>
> ---
> checkpoint/files.c | 197 +++++++++++++++++++++++++++++++++++++++-
> checkpoint/objhash.c | 9 ++
> checkpoint/process.c | 13 +++
> fs/fs_struct.c | 21 ++++
> fs/open.c | 53 ++++++-----
> include/linux/checkpoint.h | 10 ++-
> include/linux/checkpoint_hdr.h | 10 ++
> include/linux/fs.h | 4 +
> include/linux/fs_struct.h | 2 +
> 9 files changed, 293 insertions(+), 26 deletions(-)
>
> diff --git a/checkpoint/files.c b/checkpoint/files.c
> index b622588..d6cf945 100644
> --- a/checkpoint/files.c
> +++ b/checkpoint/files.c
> @@ -24,6 +24,9 @@
> #include <linux/checkpoint_hdr.h>
> #include <linux/eventpoll.h>
> #include <linux/eventfd.h>
> +#include <linux/fs.h>
> +#include <linux/fs_struct.h>
> +#include <linux/namei.h>
> #include <net/sock.h>
>
>
> @@ -449,10 +452,81 @@ int ckpt_collect_file_table(struct ckpt_ctx *ctx, struct task_struct *t)
> return ret;
> }
>
> +int checkpoint_get_task_fs(struct ckpt_ctx *ctx, struct task_struct *t)
Renaming these to {checkpoint/restore}_obj_filesystem() will be
consistent with existing naming convention there.
> +{
> + struct fs_struct *fs;
> + int fs_objref;
> +
> + task_lock(current);
> + fs = t->fs;
> + get_fs_struct(fs);
> + task_unlock(current);
> +
> + fs_objref = checkpoint_obj(ctx, fs, CKPT_OBJ_TASK_FS);
> + put_fs_struct(fs);
> +
> + return fs_objref;
> +}
> +
> +/*
> + * called with fs refcount bumped so it won't disappear
> + */
> +int checkpoint_obj_task_fs(struct ckpt_ctx *ctx, struct fs_struct *fs)
> +{
> + struct ckpt_hdr_task_fs *h;
> + int ret;
> + struct fs_struct *fscopy;
> +
> + h = ckpt_hdr_get_type(ctx, sizeof(*h), CKPT_HDR_TASK_FS);
> + if (!h)
> + return -ENOMEM;
> + ret = ckpt_write_obj(ctx, &h->h);
> + ckpt_hdr_put(ctx, h);
> + if (ret)
> + return ret;
> +
> + fscopy = copy_fs_struct(fs);
> + if (!fs)
> + return -ENOMEM;
> +
Reverse the order below: cwd first then root - this will allow
the cwd to be outside of the current chroot, in the case that
the task escaped the chroot.
> + ret = checkpoint_fname(ctx, &fscopy->root, &ctx->fs_mnt);
> + if (ret < 0) {
> + ckpt_err(ctx, ret, "%(T)writing name of fs root");
> + goto out;
> + }
> + ret = checkpoint_fname(ctx, &fscopy->pwd, &ctx->fs_mnt);
> + if (ret < 0) {
> + ckpt_err(ctx, ret, "%(T)writing name of pwd");
> + goto out;
> + }
> + ret = 0;
[...]
> +/* this is the fn called by objhash when it runs into a
> + * CKPT_OBJ_TASK_FS entry. Creates an fs_struct and
> + * places it in the hash. */
> +static struct fs_struct *restore_obj_task_fs(struct ckpt_ctx *ctx)
> +{
> + struct ckpt_hdr_task_fs *h;
> + struct fs_struct *fs;
> + int ret = 0;
> + char *root, *cwd;
> +
> + h = ckpt_read_obj_type(ctx, sizeof(*h), CKPT_HDR_TASK_FS);
> + if (IS_ERR(h))
> + return ERR_PTR(PTR_ERR(h));
> + ckpt_hdr_put(ctx, h);
> +
> + fs = copy_fs_struct(current->fs);
> + if (!fs)
> + return ERR_PTR(-ENOMEM);
> +
Please reverse the order below: restore cwd before chroot.
> + ret = ckpt_read_fname(ctx, &root);
> + if (ret < 0)
> + goto out;
> + ret = restore_chroot(ctx, fs, root);
> + kfree(root);
> + if (ret)
> + goto out;
> +
> + ret = ckpt_read_fname(ctx, &cwd);
> + if (ret < 0)
> + goto out;
> + ret = restore_cwd(ctx, fs, cwd);
> + kfree(cwd);
> +
> +out:
> + if (ret) {
> + free_fs_struct(fs);
> + return ERR_PTR(ret);
> + }
> + return fs;
> +}
> +
> +void *restore_task_fs(struct ckpt_ctx *ctx)
> +{
> + return (void *) restore_obj_task_fs(ctx);
> +}
> +
> +/*
> + * Called by task restore code to set the restarted task's
> + * current->fs to an entry on the hash
> + */
> +int restore_set_task_fs(struct ckpt_ctx *ctx, int fs_objref)
(Please rename this one, too)
> +{
> + struct fs_struct *newfs, *oldfs;
> +
> + newfs = ckpt_obj_fetch(ctx, fs_objref, CKPT_OBJ_TASK_FS);
> + if (IS_ERR(newfs))
> + return PTR_ERR(newfs);
> +
> + task_lock(current);
> + get_fs_struct(newfs);
> + oldfs = current->fs;
> + current->fs = newfs;
> + task_unlock(current);
> + put_fs_struct(oldfs);
> +
> + return 0;
> +}
> diff --git a/checkpoint/objhash.c b/checkpoint/objhash.c
> index 782661d..20fd3e9 100644
> --- a/checkpoint/objhash.c
> +++ b/checkpoint/objhash.c
> @@ -417,6 +417,15 @@ static struct ckpt_obj_ops ckpt_obj_ops[] = {
> .checkpoint = checkpoint_userns,
> .restore = restore_userns,
> },
> + /* struct fs_struct */
> + {
> + .obj_name = "TASK_FS",
> + .obj_type = CKPT_OBJ_TASK_FS,
> + .ref_drop = obj_task_fs_drop,
> + .ref_grab = obj_task_fs_grab,
> + .checkpoint = checkpoint_task_fs,
> + .restore = restore_task_fs,
I think we also need a .collect method to prevent leaks ?
> + },
> /* struct cred */
> {
> .obj_name = "CRED",
> diff --git a/checkpoint/process.c b/checkpoint/process.c
> index 9c0463d..603bbf4 100644
> --- a/checkpoint/process.c
> +++ b/checkpoint/process.c
> @@ -234,6 +234,7 @@ static int checkpoint_task_objs(struct ckpt_ctx *ctx, struct task_struct *t)
> int mm_objref;
> int sighand_objref;
> int signal_objref;
> + int fs_objref;
> int first, ret;
>
> /*
> @@ -253,6 +254,12 @@ static int checkpoint_task_objs(struct ckpt_ctx *ctx, struct task_struct *t)
> if (ret < 0)
> return ret;
>
> + fs_objref = checkpoint_get_task_fs(ctx, t);
> + if (fs_objref < 0) {
> + ckpt_err(ctx, fs_objref, "%(T)process fs\n");
> + return fs_objref;
> + }
> +
> files_objref = checkpoint_obj_file_table(ctx, t);
The fs should be saved and restored after the file-table, or otherwise
I'd expect files that were open before a task changed called chroot()
to be unreachable.
> ckpt_debug("files: objref %d\n", files_objref);
> if (files_objref < 0) {
> @@ -294,6 +301,7 @@ static int checkpoint_task_objs(struct ckpt_ctx *ctx, struct task_struct *t)
> h->mm_objref = mm_objref;
> h->sighand_objref = sighand_objref;
> h->signal_objref = signal_objref;
> + h->fs_objref = fs_objref;
> ret = ckpt_write_obj(ctx, &h->h);
> ckpt_hdr_put(ctx, h);
> if (ret < 0)
> @@ -628,6 +636,11 @@ static int restore_task_objs(struct ckpt_ctx *ctx)
> return PTR_ERR(h);
> }
>
> + ret = restore_set_task_fs(ctx, h->fs_objref);
> + ckpt_debug("restore_task_fs returned %d\n", ret);
> + if (ret < 0)
> + return ret;
> +
> ret = restore_obj_file_table(ctx, h->files_objref);
> ckpt_debug("file_table: ret %d (%p)\n", ret, current->files);
> if (ret < 0)
Here too.
> diff --git a/fs/fs_struct.c b/fs/fs_struct.c
> index eee0590..2a4c6f5 100644
> --- a/fs/fs_struct.c
> +++ b/fs/fs_struct.c
> @@ -6,6 +6,27 @@
> #include <linux/fs_struct.h>
>
> /*
> + * call with owning task locked
> + */
> +void get_fs_struct(struct fs_struct *fs)
> +{
> + write_lock(&fs->lock);
> + fs->users++;
> + write_unlock(&fs->lock);
> +}
> +
> +void put_fs_struct(struct fs_struct *fs)
> +{
> + int kill;
> +
> + write_lock(&fs->lock);
> + kill = !--fs->users;
> + write_unlock(&fs->lock);
> + if (kill)
> + free_fs_struct(fs);
> +}
I didn't look everywhere, however - could there be other users of
these two elsewhere in the kernel ?
> +
> +/*
> * Replace the fs->{rootmnt,root} with {mnt,dentry}. Put the old values.
> * It can block.
> */
[...]
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index 5ae34fc..0efa62a 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -1819,9 +1819,13 @@ extern struct vfsmount *collect_mounts(struct path *);
> extern void drop_collected_mounts(struct vfsmount *);
>
> extern int vfs_statfs(struct dentry *, struct kstatfs *);
> +struct fs_struct;
> +extern int do_chdir(struct fs_struct *fs, struct path *path);
> +extern int do_chroot(struct fs_struct *fs, struct path *path);
>
> extern int current_umask(void);
>
> +
:(
> /* /sys/fs */
> extern struct kobject *fs_kobj;
>
> diff --git a/include/linux/fs_struct.h b/include/linux/fs_struct.h
> index 78a05bf..a73cbcb 100644
> --- a/include/linux/fs_struct.h
> +++ b/include/linux/fs_struct.h
> @@ -20,5 +20,7 @@ extern struct fs_struct *copy_fs_struct(struct fs_struct *);
> extern void free_fs_struct(struct fs_struct *);
> extern void daemonize_fs_struct(void);
> extern int unshare_fs_struct(void);
> +extern void get_fs_struct(struct fs_struct *);
> +extern void put_fs_struct(struct fs_struct *);
>
> #endif /* _LINUX_FS_STRUCT_H */
Thanks,
Oren.
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