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netfs: Eliminate Clang randstruct warning 

Clang's structure layout randomization feature gets upset when it sees
struct inode (which is randomized) cast to struct netfs_i_context. This
is due to seeing the inode pointer as being treated as an array of inodes,
rather than "something else, following struct inode".

Since netfs can't use container_of() (since it doesn't know what the
true containing struct is), it uses this direct offset instead. Adjust
the code to better reflect what is happening: an arbitrary pointer is
being adjusted and cast to something else: use a "void *" for the math.
The resulting binary output is the same, but Clang no longer sees an
unexpected cross-structure cast:

In file included from ../fs/nfs/inode.c:50:
In file included from ../fs/nfs/fscache.h:15:
In file included from ../include/linux/fscache.h:18:
../include/linux/netfs.h:298:9: error: casting from randomized structure pointer type 'struct inode *' to 'struct netfs_i_context *'
        return (struct netfs_i_context *)(inode + 1);
               ^
1 error generated.

Cc: David Howells <dhowells@redhat.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20220503205503.3054173-2-keescook@chromium.org
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Link: https://lore.kernel.org/lkml/7562f8eccd7cc0e447becfe9912179088784e3b9.camel@kernel.org
This commit is contained in:
Kees Cook 2022-05-03 13:54:58 -07:00
parent e6f3b3c9c1
commit 3b5eed3c71
1 changed files with 2 additions and 2 deletions
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4
include/linux/netfs.h
View File

@ -295,7 +295,7 @@ extern void netfs_stats_show(struct seq_file *);
*/
static inline struct netfs_i_context *netfs_i_context(struct inode *inode)
{
return (struct netfs_i_context *)(inode + 1);
return (void *)inode + sizeof(*inode);
}
/**
@ -307,7 +307,7 @@ static inline struct netfs_i_context *netfs_i_context(struct inode *inode)
*/
static inline struct inode *netfs_inode(struct netfs_i_context *ctx)
{
return ((struct inode *)ctx) - 1;
return (void *)ctx - sizeof(struct inode);
}
/**