linux-kernel - [PATCH v3 2/3] mm/shmem: update file sealing comments and file checking

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Message-Id: <20180409230505.18953-3-mike.kravetz@oracle.com>
Date:   Mon,  9 Apr 2018 16:05:04 -0700
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     linux-mm@...ck.org, linux-kernel@...r.kernel.org
Cc:     Matthew Wilcox <willy@...radead.org>,
        Hugh Dickins <hughd@...gle.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Michal Hocko <mhocko@...nel.org>,
        Marc-André Lureau <marcandre.lureau@...il.com>,
        David Herrmann <dh.herrmann@...il.com>,
        Khalid Aziz <khalid.aziz@...cle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mike Kravetz <mike.kravetz@...cle.com>
Subject: [PATCH v3 2/3] mm/shmem: update file sealing comments and file checking

In preparation for memfd code restucture, update comments dealing
with file sealing to indicate that tmpfs and hugetlbfs are the
supported filesystems.  Also, change file pointer checks in
memfd_file_seals_ptr to use defined routines instead of directly
referencing file_operation structs.

Signed-off-by: Mike Kravetz <mike.kravetz@...cle.com>
---
 mm/shmem.c | 29 +++++++++++++++--------------
 1 file changed, 15 insertions(+), 14 deletions(-)

diff --git a/mm/shmem.c b/mm/shmem.c
index c7bad16fe884..be20fc388dcb 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -2734,11 +2734,11 @@ static int shmem_wait_for_pins(struct address_space *mapping)
 
 static unsigned int *memfd_file_seals_ptr(struct file *file)
 {
-	if (file->f_op == &shmem_file_operations)
+	if (shmem_file(file))
 		return &SHMEM_I(file_inode(file))->seals;
 
 #ifdef CONFIG_HUGETLBFS
-	if (file->f_op == &hugetlbfs_file_operations)
+	if (is_file_hugepages(file))
 		return &HUGETLBFS_I(file_inode(file))->seals;
 #endif
 
@@ -2758,16 +2758,17 @@ static int memfd_add_seals(struct file *file, unsigned int seals)
 
 	/*
 	 * SEALING
-	 * Sealing allows multiple parties to share a shmem-file but restrict
-	 * access to a specific subset of file operations. Seals can only be
-	 * added, but never removed. This way, mutually untrusted parties can
-	 * share common memory regions with a well-defined policy. A malicious
-	 * peer can thus never perform unwanted operations on a shared object.
+	 * Sealing allows multiple parties to share a tmpfs or hugetlbfs file
+	 * but restrict access to a specific subset of file operations. Seals
+	 * can only be added, but never removed. This way, mutually untrusted
+	 * parties can share common memory regions with a well-defined policy.
+	 * A malicious peer can thus never perform unwanted operations on a
+	 * shared object.
 	 *
-	 * Seals are only supported on special shmem-files and always affect
-	 * the whole underlying inode. Once a seal is set, it may prevent some
-	 * kinds of access to the file. Currently, the following seals are
-	 * defined:
+	 * Seals are only supported on special tmpfs or hugetlbfs files and
+	 * always affect the whole underlying inode. Once a seal is set, it
+	 * may prevent some kinds of access to the file. Currently, the
+	 * following seals are defined:
 	 *   SEAL_SEAL: Prevent further seals from being set on this file
 	 *   SEAL_SHRINK: Prevent the file from shrinking
 	 *   SEAL_GROW: Prevent the file from growing
@@ -2781,9 +2782,9 @@ static int memfd_add_seals(struct file *file, unsigned int seals)
 	 * added.
 	 *
 	 * Semantics of sealing are only defined on volatile files. Only
-	 * anonymous shmem files support sealing. More importantly, seals are
-	 * never written to disk. Therefore, there's no plan to support it on
-	 * other file types.
+	 * anonymous tmpfs and hugetlbfs files support sealing. More
+	 * importantly, seals are never written to disk. Therefore, there's
+	 * no plan to support it on other file types.
 	 */
 
 	if (!(file->f_mode & FMODE_WRITE))
-- 
2.13.6