[PATCH] proc: fix mount -t proc -o AAA

From: Vasiliy Kulikov
Date: Fri Mar 23 2012 - 13:11:02 EST


Hi Arkadiusz,

On Thu, Mar 22, 2012 at 09:03 +0100, Arkadiusz MiÅkiewicz wrote:
> Hi,
>
> I'm trying to use hidepid feature in 3.3 kernel but I'm getting weird
> things like options not being applied _sometimes_ at mount.
>
> [@ ~]# cat /proc/mounts
> sh: cat: /proc/mounts: No such file or directory
> [@ ~]# strace -e mount -f -F -s 200 mount none /proc -t proc -o hidepid=2,gid=17
> mount("none", "/proc", "proc", MS_MGC_VAL, "hidepid=2,gid=17") = 0
> [@ ~]# cat /proc/mounts
> rootfs / rootfs rw 0 0
> /dev/sda3 / xfs rw,relatime,attr2,noquota 0 0
> run /run tmpfs rw,relatime 0 0
> none /proc proc rw,relatime 0 0
>
> No hidepid, no gid - huh?
>
> [@ ~]# mount /proc -o remount,hidepid=2,gid=17
> [@ ~]# cat /proc/mounts
> rootfs / rootfs rw 0 0
> /dev/sda3 / xfs rw,relatime,attr2,noquota 0 0
> run /run tmpfs rw,relatime 0 0
> none /proc proc rw,relatime,gid=17,hidepid=2 0 0
>
> remount and hidepid/gid is there
>
> [@ ~]# umount /proc
> [@ ~]# strace -e mount -f -F -s 200 mount none /proc -t proc -o hidepid=2,gid=17
> mount("none", "/proc", "proc", MS_MGC_VAL, "hidepid=2,gid=17") = 0
> [@ ~]# cat /proc/mounts
> rootfs / rootfs rw 0 0
> /dev/sda3 / xfs rw,relatime,attr2,noquota 0 0
> run /run tmpfs rw,relatime 0 0
> none /proc proc rw,relatime,gid=17,hidepid=2 0 0
>
> and now I'm lost - every new umount & mount gets hidepid/gid right.
>
> Any ideas why initial mount fails to get hidepid/gid options applied?
> The syscall seems correct.

Thanks for the report. Please test the following patch.

--------------------------------------------------------------
From: Vasiliy Kulikov <segoon@xxxxxxxxxxxx>
Date: Fri, 23 Mar 2012 20:56:42 +0400
Subject: [PATCH] proc: fix mount -t proc -o AAA

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@xxxxxxxxxxxx>
Reported-by: Arkadiusz MiÅkiewicz <a.miskiewicz@xxxxxxxxx>
---
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);
--
1.7.0.4

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