From 73590342fc85ca207ca1e6cbc110179873a96962 Mon Sep 17 00:00:00 2001 From: Tadeusz Struk Date: Wed, 5 Oct 2022 16:29:30 -0700 Subject: libfdt: prevent integer overflow in fdt_next_tag Since fdt_next_tag() in a public API function all input parameters, including the fdt blob should not be trusted. It is possible to forge a blob with invalid property length that will cause integer overflow during offset calculation. To prevent that, validate the property length read from the blob before doing calculations. Signed-off-by: Tadeusz Struk Message-Id: <20221005232931.3016047-1-tadeusz.struk@linaro.org> Signed-off-by: David Gibson --- libfdt/fdt.c | 17 ++++++++++++----- 1 file changed, 12 insertions(+), 5 deletions(-) (limited to 'libfdt') diff --git a/libfdt/fdt.c b/libfdt/fdt.c index 90a39e8..20c6415 100644 --- a/libfdt/fdt.c +++ b/libfdt/fdt.c @@ -162,7 +162,7 @@ const void *fdt_offset_ptr(const void *fdt, int offset, unsigned int len) uint32_t fdt_next_tag(const void *fdt, int startoffset, int *nextoffset) { const fdt32_t *tagp, *lenp; - uint32_t tag; + uint32_t tag, len, sum; int offset = startoffset; const char *p; @@ -188,12 +188,19 @@ uint32_t fdt_next_tag(const void *fdt, int startoffset, int *nextoffset) lenp = fdt_offset_ptr(fdt, offset, sizeof(*lenp)); if (!can_assume(VALID_DTB) && !lenp) return FDT_END; /* premature end */ + + len = fdt32_to_cpu(*lenp); + sum = len + offset; + if (!can_assume(VALID_DTB) && + (INT_MAX <= sum || sum < (uint32_t) offset)) + return FDT_END; /* premature end */ + /* skip-name offset, length and value */ - offset += sizeof(struct fdt_property) - FDT_TAGSIZE - + fdt32_to_cpu(*lenp); + offset += sizeof(struct fdt_property) - FDT_TAGSIZE + len; + if (!can_assume(LATEST) && - fdt_version(fdt) < 0x10 && fdt32_to_cpu(*lenp) >= 8 && - ((offset - fdt32_to_cpu(*lenp)) % 8) != 0) + fdt_version(fdt) < 0x10 && len >= 8 && + ((offset - len) % 8) != 0) offset += 4; break; -- cgit v1.2.1