From mboxrd@z Thu Jan 1 00:00:00 1970 From: Tadeusz Struk Subject: [PATCH v2 1/2] libfdt: prevent integer overflow in fdt_next_tag Date: Fri, 30 Sep 2022 08:20:03 -0700 Message-ID: <20220930152004.674591-1-tadeusz.struk@linaro.org> Mime-Version: 1.0 Content-Transfer-Encoding: 8bit Return-path: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linaro.org; s=google; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:from:to:cc:subject:date; bh=sgdOKqL14yd+eVQhXQ4lHU2sZ9RqXiCCsu5egzJjzvU=; b=b6HS3xgQmcuLy13TnsVpXrnxz1IqYxVpbowiK+zrSAZ5mihsN4aY45nl5+bq9FKp46 YzDmaIpotpnBbd/w9LR3Rw1NNxMMZu7KjVuhLyxGRbU0dIgmJxgqtldH1pLEJdMsg2UN Aj3QYh0/blr5x9stIq7eUGKe5o5mTmiwyNWm1GTrUpR5fODwZhQh5pLZDUzCKxRoVR01 naAftOrhmiHrCv85VaUE6Ne/hxKe98PzqkzgAvd5YKVF9HHI4acfPe/HD7nkuD+sLySE Pkl4rd3HSOddcx+XjxPNdgXDnImqdtKrRtFkDOoxwfDONheD0cNatyD0rizi0GtdTlqL TqAw== List-ID: Content-Type: text/plain; charset="us-ascii" To: David Gibson , Rob Herring Cc: devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, devicetree-compiler-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Tadeusz Struk 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 -- v2: * Use len local variable to avoid multiple calls to fdt32_to_cpu(*lenp) * Add can_assume(VALID_DTB) to the new checks --- libfdt/fdt.c | 18 +++++++++++++----- 1 file changed, 13 insertions(+), 5 deletions(-) diff --git a/libfdt/fdt.c b/libfdt/fdt.c index 90a39e8..b7c202a 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; int offset = startoffset; const char *p; @@ -188,12 +188,20 @@ 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); + if (!can_assume(VALID_DTB) && INT_MAX <= len) + 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(VALID_DTB) && offset < 0) + return FDT_END; /* premature end */ + 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; -- 2.37.3