[PATCH] Replace pid_t in autofs4 with struct pid reference.
Serge Hallyn
serge.hallyn at canonical.com
Thu Sep 30 15:36:39 PDT 2010
Quoting Daniel Lezcano (daniel.lezcano at free.fr):
> I resurect and refreshed this old patch from
> https://lists.linux-foundation.org/pipermail/containers/2007-February/003726.html
>
> This patch makes automount to work within a container.
>
> Make autofs4 container-friendly by caching struct pid reference rather
> than pid_t and using pid_nr() to retreive a task's pid_t.
>
> ChangeLog:
> - Refreshed against linux-next (added dev-ioctl.c)
> - Fix Eric Biederman's comments - Use find_get_pid() to hold a
> reference to oz_pgrp and release while unmounting; separate out
> changes to autofs and autofs4.
> - Also rollback my earlier change to autofs_wait_queue (pid and tgid
> in the wait queue are just used to write to a userspace daemon's
> pipe).
> - Fix Cedric's comments: retain old prototype of parse_options()
> and move necessary change to its caller.
>
> Signed-off-by: Sukadev Bhattiprolu <sukadev at us.ibm.com>
> Signed-off-by: Daniel Lezcano <daniel.lezcano at free.fr>
> Cc: Ian Kent <raven at themaw.net>
> Cc: Cedric Le Goater <clg at fr.ibm.com>
> Cc: Dave Hansen <haveblue at us.ibm.com>
> Cc: Serge E. Hallyn <serge.hallyn at canonical.com>
> Cc: Eric Biederman <ebiederm at xmission.com>
> Cc: Helmut Lichtenberg <heli at tzv.fal.de>
> ---
> fs/autofs4/autofs_i.h | 28 ++++++++++++++--------------
> fs/autofs4/dev-ioctl.c | 2 +-
> fs/autofs4/inode.c | 22 ++++++++++++++++------
> fs/autofs4/root.c | 3 ++-
> fs/autofs4/waitq.c | 4 ++--
> 5 files changed, 35 insertions(+), 24 deletions(-)
>
> diff --git a/fs/autofs4/autofs_i.h b/fs/autofs4/autofs_i.h
> index 3d283ab..e7298a1 100644
> --- a/fs/autofs4/autofs_i.h
> +++ b/fs/autofs4/autofs_i.h
> @@ -39,25 +39,25 @@
> /* #define DEBUG */
>
> #ifdef DEBUG
> -#define DPRINTK(fmt, args...) \
> -do { \
> - printk(KERN_DEBUG "pid %d: %s: " fmt "\n", \
> - current->pid, __func__, ##args); \
> +#define DPRINTK(fmt, args...) \
> +do { \
> + printk(KERN_DEBUG "pid %d: %s: " fmt "\n", \
> + pid_nr(task_pid(current)), __func__, ##args); \
> } while (0)
> #else
> #define DPRINTK(fmt, args...) do {} while (0)
> #endif
>
> -#define AUTOFS_WARN(fmt, args...) \
> -do { \
> - printk(KERN_WARNING "pid %d: %s: " fmt "\n", \
> - current->pid, __func__, ##args); \
> +#define AUTOFS_WARN(fmt, args...) \
> +do { \
> + printk(KERN_WARNING "pid %d: %s: " fmt "\n", \
> + pid_nr(task_pid(current)), __func__, ##args); \
> } while (0)
>
> -#define AUTOFS_ERROR(fmt, args...) \
> -do { \
> - printk(KERN_ERR "pid %d: %s: " fmt "\n", \
> - current->pid, __func__, ##args); \
> +#define AUTOFS_ERROR(fmt, args...) \
> +do { \
> + printk(KERN_ERR "pid %d: %s: " fmt "\n", \
> + pid_nr(task_pid(current)), __func__, ##args); \
> } while (0)
>
> /* Unified info structure. This is pointed to by both the dentry and
> @@ -122,7 +122,7 @@ struct autofs_sb_info {
> u32 magic;
> int pipefd;
> struct file *pipe;
> - pid_t oz_pgrp;
> + struct pid *oz_pgrp;
> int catatonic;
> int version;
> int sub_version;
> @@ -156,7 +156,7 @@ static inline struct autofs_info *autofs4_dentry_ino(struct dentry *dentry)
> filesystem without "magic".) */
>
> static inline int autofs4_oz_mode(struct autofs_sb_info *sbi) {
> - return sbi->catatonic || task_pgrp_nr(current) == sbi->oz_pgrp;
> + return sbi->catatonic || task_pgrp(current) == sbi->oz_pgrp;
> }
>
> /* Does a dentry have some pending activity? */
> diff --git a/fs/autofs4/dev-ioctl.c b/fs/autofs4/dev-ioctl.c
> index eff9a41..94a523a 100644
> --- a/fs/autofs4/dev-ioctl.c
> +++ b/fs/autofs4/dev-ioctl.c
> @@ -377,7 +377,7 @@ static int autofs_dev_ioctl_setpipefd(struct file *fp,
> fput(pipe);
> goto out;
> }
> - sbi->oz_pgrp = task_pgrp_nr(current);
> + sbi->oz_pgrp = task_pgrp(current);
> sbi->pipefd = pipefd;
> sbi->pipe = pipe;
> sbi->catatonic = 0;
> diff --git a/fs/autofs4/inode.c b/fs/autofs4/inode.c
> index 821b2b9..b36af5a 100644
> --- a/fs/autofs4/inode.c
> +++ b/fs/autofs4/inode.c
> @@ -111,7 +111,7 @@ void autofs4_kill_sb(struct super_block *sb)
>
> /* Free wait queues, close pipe */
> autofs4_catatonic_mode(sbi);
> -
> + put_pid(sbi->oz_pgrp);
> sb->s_fs_info = NULL;
> kfree(sbi);
>
> @@ -133,7 +133,7 @@ static int autofs4_show_options(struct seq_file *m, struct vfsmount *mnt)
> seq_printf(m, ",uid=%u", root_inode->i_uid);
> if (root_inode->i_gid != 0)
> seq_printf(m, ",gid=%u", root_inode->i_gid);
> - seq_printf(m, ",pgrp=%d", sbi->oz_pgrp);
> + seq_printf(m, ",pgrp=%d", pid_nr(sbi->oz_pgrp));
> seq_printf(m, ",timeout=%lu", sbi->exp_timeout/HZ);
> seq_printf(m, ",minproto=%d", sbi->min_proto);
> seq_printf(m, ",maxproto=%d", sbi->max_proto);
> @@ -263,6 +263,7 @@ int autofs4_fill_super(struct super_block *s, void *data, int silent)
> int pipefd;
> struct autofs_sb_info *sbi;
> struct autofs_info *ino;
> + pid_t pgid;
>
> sbi = kzalloc(sizeof(*sbi), GFP_KERNEL);
> if (!sbi)
> @@ -275,7 +276,7 @@ int autofs4_fill_super(struct super_block *s, void *data, int silent)
> sbi->pipe = NULL;
> sbi->catatonic = 1;
> sbi->exp_timeout = 0;
> - sbi->oz_pgrp = task_pgrp_nr(current);
> + sbi->oz_pgrp = task_pgrp(current);
> sbi->sb = s;
> sbi->version = 0;
> sbi->sub_version = 0;
> @@ -314,7 +315,7 @@ int autofs4_fill_super(struct super_block *s, void *data, int silent)
>
> /* Can this call block? */
> if (parse_options(data, &pipefd, &root_inode->i_uid, &root_inode->i_gid,
> - &sbi->oz_pgrp, &sbi->type, &sbi->min_proto,
> + &pgid, &sbi->type, &sbi->min_proto,
> &sbi->max_proto)) {
> printk("autofs: called with bogus options\n");
> goto fail_dput;
> @@ -342,12 +343,19 @@ int autofs4_fill_super(struct super_block *s, void *data, int silent)
> sbi->version = sbi->max_proto;
> sbi->sub_version = AUTOFS_PROTO_SUBVERSION;
>
> - DPRINTK("pipe fd = %d, pgrp = %u", pipefd, sbi->oz_pgrp);
> + DPRINTK("pipe fd = %d, pgrp = %u", pipefd, pgid);
> +
> + sbi->oz_pgrp = find_get_pid(pgid);
This is a little backward. You first get current's pgid pid, but don't
take a reference; then parse_options gets current's pgid pid_nr (and
keeps that if no pgid was specified), passes that back here, and here we
get the pid_nr and take a ref. I was actually first going to say that
I didn't want to block this patch on this, but it should be cleaned up
at some point (i.e. at top of this function get the struct pid and get
a ref, pass that to parse_options, and have parse_options get the
specified pgid instead if a valid one was passed in.
But now I'm wondering whether this actually is unsafe, bc I'm not quite
sure how to read the comment above task_pgrp() (in sched.h) says not
to dereference this if it wasn't gotten under task_lock or rcu_read_lock.
Which this isn't. So is this actually unsafe?
> + if (!sbi->oz_pgrp) {
> + printk("autofs: could not find process group %d\n", pgid);
> + goto fail_dput;
> + }
> +
> pipe = fget(pipefd);
thanks,
-serge
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