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, 9 insertions, 14 deletions

diff --git a/fs/afs/internal.h b/fs/afs/internal.h
index a30995901266..984b113a9107 100644
--- a/fs/afs/internal.h
+++ b/fs/afs/internal.h
@@ -619,12 +619,7 @@ enum afs_lock_state {
  * leak from one inode to another.
  */
 struct afs_vnode {
-	struct {
-		/* These must be contiguous */
-		struct inode	vfs_inode;	/* the VFS's inode record */
-		struct netfs_i_context netfs_ctx; /* Netfslib context */
-	};
-
+	struct netfs_inode	netfs;		/* Netfslib context and vfs inode */
 	struct afs_volume	*volume;	/* volume on which vnode resides */
 	struct afs_fid		fid;		/* the file identifier for this inode */
 	struct afs_file_status	status;		/* AFS status info for this file */
@@ -675,7 +670,7 @@ struct afs_vnode {
 static inline struct fscache_cookie *afs_vnode_cache(struct afs_vnode *vnode)
 {
 #ifdef CONFIG_AFS_FSCACHE
-	return netfs_i_cookie(&vnode->vfs_inode);
+	return netfs_i_cookie(&vnode->netfs.inode);
 #else
 	return NULL;
 #endif
@@ -685,7 +680,7 @@ static inline void afs_vnode_set_cache(struct afs_vnode *vnode,
 				       struct fscache_cookie *cookie)
 {
 #ifdef CONFIG_AFS_FSCACHE
-	vnode->netfs_ctx.cache = cookie;
+	vnode->netfs.cache = cookie;
 #endif
 }
 
@@ -892,7 +887,7 @@ static inline void afs_invalidate_cache(struct afs_vnode *vnode, unsigned int fl
 
 	afs_set_cache_aux(vnode, &aux);
 	fscache_invalidate(afs_vnode_cache(vnode), &aux,
-			   i_size_read(&vnode->vfs_inode), flags);
+			   i_size_read(&vnode->netfs.inode), flags);
 }
 
 /*
@@ -1217,7 +1212,7 @@ static inline struct afs_net *afs_i2net(struct inode *inode)
 
 static inline struct afs_net *afs_v2net(struct afs_vnode *vnode)
 {
-	return afs_i2net(&vnode->vfs_inode);
+	return afs_i2net(&vnode->netfs.inode);
 }
 
 static inline struct afs_net *afs_sock2net(struct sock *sk)
@@ -1593,12 +1588,12 @@ extern void yfs_fs_store_opaque_acl2(struct afs_operation *);
  */
 static inline struct afs_vnode *AFS_FS_I(struct inode *inode)
 {
-	return container_of(inode, struct afs_vnode, vfs_inode);
+	return container_of(inode, struct afs_vnode, netfs.inode);
 }
 
 static inline struct inode *AFS_VNODE_TO_I(struct afs_vnode *vnode)
 {
-	return &vnode->vfs_inode;
+	return &vnode->netfs.inode;
 }
 
 /*
@@ -1621,8 +1616,8 @@ static inline void afs_update_dentry_version(struct afs_operation *op,
  */
 static inline void afs_set_i_size(struct afs_vnode *vnode, u64 size)
 {
-	i_size_write(&vnode->vfs_inode, size);
-	vnode->vfs_inode.i_blocks = ((size + 1023) >> 10) << 1;
+	i_size_write(&vnode->netfs.inode, size);
+	vnode->netfs.inode.i_blocks = ((size + 1023) >> 10) << 1;
 }
 
 /*