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[fdt] Allow for parsing device trees where the length is known in advance

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Allow for parsing device trees where an external factor (such as a
downloaded image length) determines the maximum length, which must be
validated against the length within the device tree header.

Signed-off-by: Michael Brown <mcb30@ipxe.org>
This commit is contained in:
Michael Brown
2025-03-28 14:08:18 +00:00
parent 2399c79980
commit 3860313dd5
4 changed files with 20 additions and 4 deletions
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18
src/core/fdt.c
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@@ -82,7 +82,7 @@ static int fdt_traverse ( struct fdt *fdt,
size_t len;
/* Sanity checks */
assert ( pos->offset < fdt->len );
assert ( pos->offset <= fdt->len );
assert ( ( pos->offset & ( FDT_STRUCTURE_ALIGN - 1 ) ) == 0 );
/* Clear descriptor */
@@ -453,14 +453,28 @@ int fdt_mac ( struct fdt *fdt, unsigned int offset,
*
* @v fdt Device tree
* @v hdr Device tree header
* @v max_len Maximum device tree length
* @ret rc Return status code
*/
int fdt_parse ( struct fdt *fdt, const struct fdt_header *hdr ) {
int fdt_parse ( struct fdt *fdt, const struct fdt_header *hdr,
size_t max_len ) {
const uint8_t *end;
/* Sanity check */
if ( sizeof ( fdt ) > max_len ) {
DBGC ( fdt, "FDT length %#zx too short for header\n",
max_len );
goto err;
}
/* Record device tree location */
fdt->hdr = hdr;
fdt->len = be32_to_cpu ( hdr->totalsize );
if ( fdt->len > max_len ) {
DBGC ( fdt, "FDT has invalid length %#zx / %#zx\n",
fdt->len, max_len );
goto err;
}
DBGC ( fdt, "FDT version %d at %p+%#04zx\n",
be32_to_cpu ( hdr->version ), fdt->hdr, fdt->len );