[PATCH 38/45] libfdt: Safer access to memory reservations

[Sebastian Huber]

From: David Gibson <david at gibson.dropbear.id.au>

fdt_num_mem_rsv() and fdt_get_mem_rsv() currently don't sanity check their
parameters, or the memory reserve section offset in the header.  That means
that on a corrupted blob they could access outside of the range of memory
that they should.

This improves their safety checking, meaning they shouldn't access outside
the blob's bounds, even if its contents are badly corrupted.

Signed-off-by: David Gibson <david at gibson.dropbear.id.au>
Tested-by: Alexey Kardashevskiy <aik at ozlabs.ru>
Reviewed-by: Alexey Kardashevskiy <aik at ozlabs.ru>
Reviewed-by: Simon Glass <sjg at chromium.org>
---
 cpukit/dtc/libfdt/fdt_ro.c | 33 +++++++++++++++++++++++++++------
 1 file changed, 27 insertions(+), 6 deletions(-)

diff --git a/cpukit/dtc/libfdt/fdt_ro.c b/cpukit/dtc/libfdt/fdt_ro.c
index d4cec0efd1..c74b9629af 100644
--- a/cpukit/dtc/libfdt/fdt_ro.c
+++ b/cpukit/dtc/libfdt/fdt_ro.c
@@ -170,21 +170,42 @@ uint32_t fdt_get_max_phandle(const void *fdt)
 	return 0;
 }
 
+static const struct fdt_reserve_entry *fdt_mem_rsv(const void *fdt, int n)
+{
+	int offset = n * sizeof(struct fdt_reserve_entry);
+	int absoffset = fdt_off_mem_rsvmap(fdt) + offset;
+
+	if (absoffset < fdt_off_mem_rsvmap(fdt))
+		return NULL;
+	if (absoffset > fdt_totalsize(fdt) - sizeof(struct fdt_reserve_entry))
+		return NULL;
+	return fdt_mem_rsv_(fdt, n);
+}
+
 int fdt_get_mem_rsv(const void *fdt, int n, uint64_t *address, uint64_t *size)
 {
+	const struct fdt_reserve_entry *re;
+
 	FDT_RO_PROBE(fdt);
-	*address = fdt64_to_cpu(fdt_mem_rsv_(fdt, n)->address);
-	*size = fdt64_to_cpu(fdt_mem_rsv_(fdt, n)->size);
+	re = fdt_mem_rsv(fdt, n);
+	if (!re)
+		return -FDT_ERR_BADOFFSET;
+
+	*address = fdt64_to_cpu(re->address);
+	*size = fdt64_to_cpu(re->size);
 	return 0;
 }
 
 int fdt_num_mem_rsv(const void *fdt)
 {
-	int i = 0;
+	int i;
+	const struct fdt_reserve_entry *re;
 
-	while (fdt64_to_cpu(fdt_mem_rsv_(fdt, i)->size) != 0)
-		i++;
-	return i;
+	for (i = 0; (re = fdt_mem_rsv(fdt, i)) != NULL; i++) {
+		if (fdt64_to_cpu(re->size) == 0)
+			return i;
+	}
+	return -FDT_ERR_TRUNCATED;
 }
 
 static int nextprop_(const void *fdt, int offset)
-- 
2.13.7