linux-kernel - [PATCH v3 09/25] fs: add is_userns

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Message-Id: <20200218143411.2389182-10-christian.brauner@ubuntu.com>
Date:   Tue, 18 Feb 2020 15:33:55 +0100
From:   Christian Brauner <christian.brauner@...ntu.com>
To:     Stéphane Graber <stgraber@...ntu.com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Aleksa Sarai <cyphar@...har.com>, Jann Horn <jannh@...gle.com>
Cc:     smbarber@...omium.org, Seth Forshee <seth.forshee@...onical.com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Alexey Dobriyan <adobriyan@...il.com>,
        Serge Hallyn <serge@...lyn.com>,
        James Morris <jmorris@...ei.org>,
        Kees Cook <keescook@...omium.org>,
        Jonathan Corbet <corbet@....net>,
        Phil Estes <estesp@...il.com>, linux-kernel@...r.kernel.org,
        linux-fsdevel@...r.kernel.org,
        containers@...ts.linux-foundation.org,
        linux-security-module@...r.kernel.org, linux-api@...r.kernel.org,
        Christian Brauner <christian.brauner@...ntu.com>
Subject: [PATCH v3 09/25] fs: add is_userns_visible() helper

Introduce a helper which makes it possible to detect fileystems whose
superblock is visible in multiple user namespace. This currently only
means proc and sys. Such filesystems usually have special semantics so their
behavior will not be changed with the introduction of fsid mappings.

Signed-off-by: Christian Brauner <christian.brauner@...ntu.com>
---
/* v2 */
unchanged

/* v3 */
unchanged
---
 include/linux/fs.h | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 3cd4fe6b845e..fdc8fb2d786b 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -3651,4 +3651,9 @@ static inline int inode_drain_writes(struct inode *inode)
 	return filemap_write_and_wait(inode->i_mapping);
 }
 
+static inline bool is_userns_visible(unsigned long iflags)
+{
+	return (iflags & SB_I_USERNS_VISIBLE);
+}
+
 #endif /* _LINUX_FS_H */
-- 
2.25.0