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libfdt: Check that there is only one root node

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At present it is possible to have two root nodes and even access nodes
in the 'second' root. Such trees should not be considered valid. This
was discovered as part of a security investigation into U-Boot verified
boot.

Add a check for this to fdt_check_full().

Signed-off-by: Simon Glass <sjg@chromium.org>
Reported-by: Arie Haenel <arie.haenel@intel.com>
Reported-by: Julien Lenoir <julien.lenoir@intel.com>
Message-Id: <20210323000926.3210733-1-sjg@chromium.org>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
This commit is contained in:
Simon Glass 2021-03-23 13:09:25 +13:00 • committed by David Gibson
parent 34d708249a
commit 4ca61f84dc
6 changed files with 32 additions and 2 deletions
Download patch file Download diff file Expand all files Collapse all files

7
libfdt/fdt_check.c
View file

@ -19,6 +19,7 @@ int fdt_check_full(const void *fdt, size_t bufsize)
unsigned int depth = 0;
const void *prop;
const char *propname;
bool expect_end = false;
if (bufsize < FDT_V1_SIZE)
return -FDT_ERR_TRUNCATED;
@ -41,6 +42,10 @@ int fdt_check_full(const void *fdt, size_t bufsize)
if (nextoffset < 0)
return nextoffset;
/* If we see two root nodes, something is wrong */
if (expect_end && tag != FDT_END)
return -FDT_ERR_BADSTRUCTURE;
switch (tag) {
case FDT_NOP:
break;
@ -60,6 +65,8 @@ int fdt_check_full(const void *fdt, size_t bufsize)
if (depth == 0)
return -FDT_ERR_BADSTRUCTURE;
depth--;
if (depth == 0)
expect_end = true;
break;
case FDT_PROP: