netfs: Fix gcc-12 warning by embedding vfs inode in netfs_i_context

While randstruct was satisfied with using an open-coded "void *" offset
cast for the netfs_i_context <-> inode casting, __builtin_object_size() as
used by FORTIFY_SOURCE was not as easily fooled.  This was causing the
following complaint[1] from gcc v12:

  In file included from include/linux/string.h:253,
                   from include/linux/ceph/ceph_debug.h:7,
                   from fs/ceph/inode.c:2:
  In function 'fortify_memset_chk',
      inlined from 'netfs_i_context_init' at include/linux/netfs.h:326:2,
      inlined from 'ceph_alloc_inode' at fs/ceph/inode.c:463:2:
  include/linux/fortify-string.h:242:25: warning: call to '__write_overflow_field' declared with attribute warning: detected write beyond size of field (1st parameter); maybe use struct_group()? [-Wattribute-warning]
    242 |                         __write_overflow_field(p_size_field, size);
        |                         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Fix this by embedding a struct inode into struct netfs_i_context (which
should perhaps be renamed to struct netfs_inode).  The struct inode
vfs_inode fields are then removed from the 9p, afs, ceph and cifs inode
structs and vfs_inode is then simply changed to "netfs.inode" in those
filesystems.

Further, rename netfs_i_context to netfs_inode, get rid of the
netfs_inode() function that converted a netfs_i_context pointer to an
inode pointer (that can now be done with &ctx->inode) and rename the
netfs_i_context() function to netfs_inode() (which is now a wrapper
around container_of()).

Most of the changes were done with:

  perl -p -i -e 's/vfs_inode/netfs.inode/'g \
        `git grep -l 'vfs_inode' -- fs/{9p,afs,ceph,cifs}/*.[ch]`

Kees suggested doing it with a pair structure[2] and a special
declarator to insert that into the network filesystem's inode
wrapper[3], but I think it's cleaner to embed it - and then it doesn't
matter if struct randomisation reorders things.

Dave Chinner suggested using a filesystem-specific VFS_I() function in
each filesystem to convert that filesystem's own inode wrapper struct
into the VFS inode struct[4].

Version #2:
 - Fix a couple of missed name changes due to a disabled cifs option.
 - Rename nfs_i_context to nfs_inode
 - Use "netfs" instead of "nic" as the member name in per-fs inode wrapper
   structs.

[ This also undoes commit 507160f46c55 ("netfs: gcc-12: temporarily
  disable '-Wattribute-warning' for now") that is no longer needed ]

Fixes: bc899ee1c898 ("netfs: Add a netfs inode context")
Reported-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Xiubo Li <xiubli@redhat.com>
cc: Jonathan Corbet <corbet@lwn.net>
cc: Eric Van Hensbergen <ericvh@gmail.com>
cc: Latchesar Ionkov <lucho@ionkov.net>
cc: Dominique Martinet <asmadeus@codewreck.org>
cc: Christian Schoenebeck <linux_oss@crudebyte.com>
cc: Marc Dionne <marc.dionne@auristor.com>
cc: Ilya Dryomov <idryomov@gmail.com>
cc: Steve French <smfrench@gmail.com>
cc: William Kucharski <william.kucharski@oracle.com>
cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>
cc: Dave Chinner <david@fromorbit.com>
cc: linux-doc@vger.kernel.org
cc: v9fs-developer@lists.sourceforge.net
cc: linux-afs@lists.infradead.org
cc: ceph-devel@vger.kernel.org
cc: linux-cifs@vger.kernel.org
cc: samba-technical@lists.samba.org
cc: linux-fsdevel@vger.kernel.org
cc: linux-hardening@vger.kernel.org
Link: https://lore.kernel.org/r/d2ad3a3d7bdd794c6efb562d2f2b655fb67756b9.camel@kernel.org/ [1]
Link: https://lore.kernel.org/r/20220517210230.864239-1-keescook@chromium.org/ [2]
Link: https://lore.kernel.org/r/20220518202212.2322058-1-keescook@chromium.org/ [3]
Link: https://lore.kernel.org/r/20220524101205.GI2306852@dread.disaster.area/ [4]
Link: https://lore.kernel.org/r/165296786831.3591209.12111293034669289733.stgit@warthog.procyon.org.uk/ # v1
Link: https://lore.kernel.org/r/165305805651.4094995.7763502506786714216.stgit@warthog.procyon.org.uk # v2
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 16 insertions, 25 deletions

diff --git a/include/linux/netfs.h b/include/linux/netfs.h
index 77fa6a61706a..6dbb4c9ce50d 100644
--- a/include/linux/netfs.h
+++ b/include/linux/netfs.h
@@ -119,9 +119,10 @@ typedef void (*netfs_io_terminated_t)(void *priv, ssize_t transferred_or_error,
 				      bool was_async);
 
 /*
- * Per-inode description.  This must be directly after the inode struct.
+ * Per-inode context.  This wraps the VFS inode.
  */
-struct netfs_i_context {
+struct netfs_inode {
+	struct inode		inode;		/* The VFS inode */
 	const struct netfs_request_ops *ops;
 #if IS_ENABLED(CONFIG_FSCACHE)
 	struct fscache_cookie	*cache;
@@ -256,7 +257,7 @@ struct netfs_cache_ops {
 	 * boundary as appropriate.
 	 */
 	enum netfs_io_source (*prepare_read)(struct netfs_io_subrequest *subreq,
-					       loff_t i_size);
+					     loff_t i_size);
 
 	/* Prepare a write operation, working out what part of the write we can
 	 * actually do.
@@ -288,45 +289,35 @@ extern void netfs_put_subrequest(struct netfs_io_subrequest *subreq,
 extern void netfs_stats_show(struct seq_file *);
 
 /**
- * netfs_i_context - Get the netfs inode context from the inode
+ * netfs_inode - Get the netfs inode context from the inode
  * @inode: The inode to query
  *
  * Get the netfs lib inode context from the network filesystem's inode.  The
  * context struct is expected to directly follow on from the VFS inode struct.
  */
-static inline struct netfs_i_context *netfs_i_context(struct inode *inode)
+static inline struct netfs_inode *netfs_inode(struct inode *inode)
 {
-	return (void *)inode + sizeof(*inode);
+	return container_of(inode, struct netfs_inode, inode);
 }
 
 /**
- * netfs_inode - Get the netfs inode from the inode context
- * @ctx: The context to query
- *
- * Get the netfs inode from the netfs library's inode context.  The VFS inode
- * is expected to directly precede the context struct.
- */
-static inline struct inode *netfs_inode(struct netfs_i_context *ctx)
-{
-	return (void *)ctx - sizeof(struct inode);
-}
-
-/**
- * netfs_i_context_init - Initialise a netfs lib context
+ * netfs_inode_init - Initialise a netfslib inode context
  * @inode: The inode with which the context is associated
  * @ops: The netfs's operations list
  *
  * Initialise the netfs library context struct.  This is expected to follow on
  * directly from the VFS inode struct.
  */
-static inline void netfs_i_context_init(struct inode *inode,
-					const struct netfs_request_ops *ops)
+static inline void netfs_inode_init(struct inode *inode,
+				    const struct netfs_request_ops *ops)
 {
-	struct netfs_i_context *ctx = netfs_i_context(inode);
+	struct netfs_inode *ctx = netfs_inode(inode);
 
-	memset(ctx, 0, sizeof(*ctx));
 	ctx->ops = ops;
 	ctx->remote_i_size = i_size_read(inode);
+#if IS_ENABLED(CONFIG_FSCACHE)
+	ctx->cache = NULL;
+#endif
 }
 
 /**
@@ -338,7 +329,7 @@ static inline void netfs_i_context_init(struct inode *inode,
  */
 static inline void netfs_resize_file(struct inode *inode, loff_t new_i_size)
 {
-	struct netfs_i_context *ctx = netfs_i_context(inode);
+	struct netfs_inode *ctx = netfs_inode(inode);
 
 	ctx->remote_i_size = new_i_size;
 }
@@ -352,7 +343,7 @@ static inline void netfs_resize_file(struct inode *inode, loff_t new_i_size)
 static inline struct fscache_cookie *netfs_i_cookie(struct inode *inode)
 {
 #if IS_ENABLED(CONFIG_FSCACHE)
-	struct netfs_i_context *ctx = netfs_i_context(inode);
+	struct netfs_inode *ctx = netfs_inode(inode);
 	return ctx->cache;
 #else
 	return NULL;