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libfs: Modify mount_pseudo_xattr to be clear it is not a userspace mount

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[ Upstream commit 75422726b0 ]

Add MS_KERNMOUNT to the flags that are passed.
Use sget_userns and force &init_user_ns instead of calling sget so that
even if called from a weird context the internal filesystem will be
considered to be in the intial user namespace.

Luis Ressel reported that the the failure to pass MS_KERNMOUNT into
mount_pseudo broke his in development graphics driver that uses the
generic drm infrastructure.  I am not certain the deriver was bug
free in it's usage of that infrastructure but since
mount_pseudo_xattr can never be triggered by userspace it is clearer
and less error prone, and less problematic for the code to be explicit.

Reported-by: Luis Ressel <aranea@aixah.de>
Tested-by: Luis Ressel <aranea@aixah.de>
Acked-by: Al Viro <viro@ZenIV.linux.org.uk>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Sasha Levin <alexander.levin@verizon.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Eric W. Biederman 2017-01-04 17:37:27 +13:00 committed by Greg Kroah-Hartman
parent d9a4e70f23
commit c4081f9198
1 changed files with 2 additions and 1 deletions
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3
fs/libfs.c
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@ -245,7 +245,8 @@ struct dentry *mount_pseudo_xattr(struct file_system_type *fs_type, char *name,
struct inode *root;
struct qstr d_name = QSTR_INIT(name, strlen(name));
s = sget(fs_type, NULL, set_anon_super, MS_NOUSER, NULL);
s = sget_userns(fs_type, NULL, set_anon_super, MS_KERNMOUNT|MS_NOUSER,
&init_user_ns, NULL);
if (IS_ERR(s))
return ERR_CAST(s);