jffs2: pass the correct prototype to read_cache_page

Fix the callback jffs2 passes to read_cache_page to actually have the
proper type expected.  Casting around function pointers can easily hide
typing bugs, and defeats control flow protection.

Link: http://lkml.kernel.org/r/20190520055731.24538-4-hch@lst.deSigned-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Kees Cook <keescook@chromium.org>
Cc: Nick Desaulniers <ndesaulniers@google.com>
Cc: Sami Tolvanen <samitolvanen@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/jffs2/file.c

@@ -109,9 +109,9 @@ static int jffs2_do_readpage_nolock (struct inode *inode, struct page *pg)
 	return ret;
 }
 
-int jffs2_do_readpage_unlock(struct inode *inode, struct page *pg)
+int jffs2_do_readpage_unlock(void *data, struct page *pg)
 {
-	int ret = jffs2_do_readpage_nolock(inode, pg);
+	int ret = jffs2_do_readpage_nolock(data, pg);
 	unlock_page(pg);
 	return ret;
 }

fs/jffs2/fs.c

@@ -687,7 +687,7 @@ unsigned char *jffs2_gc_fetch_page(struct jffs2_sb_info *c,
 	struct page *pg;
 
 	pg = read_cache_page(inode->i_mapping, offset >> PAGE_SHIFT,
-			     (void *)jffs2_do_readpage_unlock, inode);
+			     jffs2_do_readpage_unlock, inode);
 	if (IS_ERR(pg))
 		return (void *)pg;
 

fs/jffs2/os-linux.h

@@ -155,7 +155,7 @@ extern const struct file_operations jffs2_file_operations;
 extern const struct inode_operations jffs2_file_inode_operations;
 extern const struct address_space_operations jffs2_file_address_operations;
 int jffs2_fsync(struct file *, loff_t, loff_t, int);
-int jffs2_do_readpage_unlock (struct inode *inode, struct page *pg);
+int jffs2_do_readpage_unlock(void *data, struct page *pg);
 
 /* ioctl.c */
 long jffs2_ioctl(struct file *, unsigned int, unsigned long);