libfdt: Rework/cleanup fdt_next_tag()

Currently, callers of fdt_next_tag() must usually follow the call with
some sort of call to fdt_offset_ptr() to verify that the blob isn't
truncated in the middle of the tag data they're going to process.
This is a bit silly, since fdt_next_tag() generally has to call
fdt_offset_ptr() on at least some of the data following the tag for
its own operation.

This patch alters fdt_next_tag() to always use fdt_offset_ptr() to
verify the data between its starting offset and the offset it returns
in nextoffset.  This simplifies fdt_get_property() which no longer has
to verify itself that the property data is all present.

At the same time, I neaten and clarify the error handling for
fdt_next_tag().  Previously, fdt_next_tag() could return -1 instead of
a tag value in some circumstances - which almost none of the callers
checked for.  Also, fdt_next_tag() could return FDT_END either because
it encountered an FDT_END tag, or because it reached the end of the
structure block - no way was provided to tell between these cases.

With this patch, fdt_next_tag() always returns FDT_END with a negative
value in nextoffset for an error.  This means the several places which
loop looking for FDT_END will still work correctly - they only need to
check for errors at the end.  The errors which fdt_next_tag() can
report are:
	- -FDT_ERR_TRUNCATED if it reached the end of the structure
	   block instead of finding a tag.

	- -FDT_BADSTRUCTURE if a bad tag was encountered, or if the
           tag data couldn't be verified with fdt_offset_ptr().

This patch also updates the callers of fdt_next_tag(), where
appropriate, to make use of the new error reporting.

Finally, the prototype for the long gone _fdt_next_tag() is removed
from libfdt_internal.h.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

1 files changed, 4 insertions, 5 deletions

diff --git a/libfdt/fdt_sw.c b/libfdt/fdt_sw.c
index 698329e0cc..2380b27502 100644
--- a/libfdt/fdt_sw.c
+++ b/libfdt/fdt_sw.c
@@ -82,7 +82,7 @@ static void *_fdt_grab_space(void *fdt, int len)
 		return NULL;
 
 	fdt_set_size_dt_struct(fdt, offset + len);
-	return fdt_offset_ptr_w(fdt, offset, len);
+	return _fdt_offset_ptr_w(fdt, offset);
 }
 
 int fdt_create(void *buf, int bufsize)
@@ -237,18 +237,17 @@ int fdt_finish(void *fdt)
 	while ((tag = fdt_next_tag(fdt, offset, &nextoffset)) != FDT_END) {
 		if (tag == FDT_PROP) {
 			struct fdt_property *prop =
-				fdt_offset_ptr_w(fdt, offset, sizeof(*prop));
+				_fdt_offset_ptr_w(fdt, offset);
 			int nameoff;
 
-			if (! prop)
-				return -FDT_ERR_BADSTRUCTURE;
-
 			nameoff = fdt32_to_cpu(prop->nameoff);
 			nameoff += fdt_size_dt_strings(fdt);
 			prop->nameoff = cpu_to_fdt32(nameoff);
 		}
 		offset = nextoffset;
 	}
+	if (nextoffset < 0)
+		return nextoffset;
 
 	/* Finally, adjust the header */
 	fdt_set_totalsize(fdt, newstroffset + fdt_size_dt_strings(fdt));