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SubjectRe: [PATCH] proc: fix mount -t proc -o AAA
Date
On Saturday 24 of March 2012, Andrew Morton wrote:
> On Fri, 23 Mar 2012 21:10:58 +0400
>
> Vasiliy Kulikov <segoon@openwall.com> wrote:
> > proc_parse_options() inside of proc_mount() runs only once at the boot
> > time without any given options. So, following umount(2)+mount(2) ignore
> > mount options: proc_parse_options() is not called as ->s_root is already
> > initialized. To fix that parse mount options unconditionally.
> >
> > Signed-off-by: Vasiliy Kulikov <segoon@openwall.com>
> > Reported-by: Arkadiusz Mi__kiewicz <a.miskiewicz@gmail.com>
> > ---
> >
> > fs/proc/root.c | 9 +++++----
> > 1 files changed, 5 insertions(+), 4 deletions(-)
> >
> > diff --git a/fs/proc/root.c b/fs/proc/root.c
> > index 46a15d8..eed44bf 100644
> > --- a/fs/proc/root.c
> > +++ b/fs/proc/root.c
> > @@ -115,12 +115,13 @@ static struct dentry *proc_mount(struct
> > file_system_type *fs_type,
> >
> > if (IS_ERR(sb))
> >
> > return ERR_CAST(sb);
> >
> > + if (!proc_parse_options(options, ns)) {
> > + deactivate_locked_super(sb);
> > + return ERR_PTR(-EINVAL);
> > + }
> > +
> >
> > if (!sb->s_root) {
> >
> > sb->s_flags = flags;
> >
> > - if (!proc_parse_options(options, ns)) {
> > - deactivate_locked_super(sb);
> > - return ERR_PTR(-EINVAL);
> > - }
> >
> > err = proc_fill_super(sb);
> > if (err) {
> >
> > deactivate_locked_super(sb);
>
> I'm surprised. "mount -o remount,<options>" doesn't work on a mounted
> procfs, and nobody noticed until now?

For me initial mount -o options didn't apply these options. Then mount -o
remount,options applied these.

> The patch looks OK - has it been tested with both valid and invalid
> mount options?

Well, it fixes my initial case where initial mount failed to apply options.

Just tested with invalid options.

[ 18.518529] proc: unrecognized mount option "crap" or missing value

but there is another problem - unmounting it and mounting without options
causes old option to persist:

# mount none /proc -t proc -o hidepid=2
# umount /proc
# mount none /proc -t proc
# grep "/proc" /proc/mounts
none /proc proc rw,relatime,hidepid=2 0 0

There should be no hidepid=2 now.

> I redid the changelog:
>
>
> From: Vasiliy Kulikov <segoon@openwall.com>
> Subject: proc: fix mount -t proc -o AAA
>
> The proc_parse_options() call from proc_mount() runs only once at boot
> time. So on any later mount attempt, any mount options are ignored
> because ->s_root is already initialized.
>
> As a consequence, "mount -o remount,<options>" will ignore the options.

So this changelog doesn't match what I saw.

>
> To fix this, parse the mount options unconditionally.
>
> Signed-off-by: Vasiliy Kulikov <segoon@openwall.com>
> Reported-by: Arkadiusz Miskiewicz <a.miskiewicz@gmail.com>
> Cc: Alexey Dobriyan <adobriyan@gmail.com>
> Cc: Al Viro <viro@zeniv.linux.org.uk>
> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
> ---
>
> fs/proc/root.c | 9 +++++----
> 1 file changed, 5 insertions(+), 4 deletions(-)
>
> diff -puN fs/proc/root.c~proc-fix-mount-t-proc-o-aaa fs/proc/root.c
> --- a/fs/proc/root.c~proc-fix-mount-t-proc-o-aaa
> +++ a/fs/proc/root.c
> @@ -115,12 +115,13 @@ static struct dentry *proc_mount(struct
> if (IS_ERR(sb))
> return ERR_CAST(sb);
>
> + if (!proc_parse_options(options, ns)) {
> + deactivate_locked_super(sb);
> + return ERR_PTR(-EINVAL);
> + }
> +
> if (!sb->s_root) {
> sb->s_flags = flags;
> - if (!proc_parse_options(options, ns)) {
> - deactivate_locked_super(sb);
> - return ERR_PTR(-EINVAL);
> - }
> err = proc_fill_super(sb);
> if (err) {
> deactivate_locked_super(sb);
> _


--
Arkadiusz Miśkiewicz PLD/Linux Team
arekm / maven.pl http://ftp.pld-linux.org/
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