From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtpout-02.galae.net (smtpout-02.galae.net [185.246.84.56]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id E3D283B71CE; Wed, 26 Aug 2026 08:32:59 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=185.246.84.56 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787733181; cv=none; b=Jvn/EcohLloC0g0T1jy7iAksaDRgsarIbnz/np5RMdw+ii8JJGJkJIAJU6xwlSMsNfdVrtiFeI+oE66bvyz0U96OS4ElM2s448VMCT8vzItQaPXdGD1Io9Yvo3g2opLKJcKJUsZ/ax1Wvj+pz0TIS8RAzm4oxSwm2Mcv7C/nY40= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787733181; c=relaxed/simple; bh=ryj6qtC+rieClZ3/ur+Ak/VqTR1urmgK0jCffZjuyz8=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=ZBQp3C2Z6CQeWsesrJQtMkGn+zPpnGdP++kKzliWoKMfIOnfomC0iLx2RyMQs4lHvUyR7RJvFaabEaL1BQLmP/aBVhkVfHsLKs+P4jb1Utr/gn+XsO2JlwDawV9NhBKg4zaGG1KaLcG//QtDg6JCNfpI7ydwPY/XrqtPjxh2gMo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=bootlin.com; spf=pass smtp.mailfrom=bootlin.com; dkim=pass (2048-bit key) header.d=bootlin.com header.i=@bootlin.com header.b=boas6wea; arc=none smtp.client-ip=185.246.84.56 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=bootlin.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=bootlin.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=bootlin.com header.i=@bootlin.com header.b="boas6wea" Received: from smtpout-01.galae.net (smtpout-01.galae.net [212.83.139.233]) by smtpout-02.galae.net (Postfix) with ESMTPS id 92FBE1A1844; Wed, 26 Aug 2026 08:32:58 +0000 (UTC) Received: from mail.galae.net (mail.galae.net [212.83.136.155]) by smtpout-01.galae.net (Postfix) with ESMTPS id 67BBA604EC; Wed, 26 Aug 2026 08:32:58 +0000 (UTC) Received: from [127.0.0.1] (localhost [127.0.0.1]) by localhost (Mailerdaemon) with ESMTPSA id D8C6811C7AC4A; Wed, 26 Aug 2026 10:32:55 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=bootlin.com; s=dkim; t=1787733177; h=from:subject:date:message-id:to:cc:mime-version: content-transfer-encoding:in-reply-to:references; bh=t87Xr7v6Qr55Y1xfzRrTbV4rvY3L3qyedBD8I8H65Hc=; b=boas6weaJXVkiMVNkq0z/TXWKJyq9tROa07RhEVafPtuejLCPiFrQffJLu1GA/74A7l1yq mrBagvnPKrZR6wMFnOy80kPzN48oCfkoNkkaTpXuiOc3QLH1NcMRI+JrhUZxp7BXmF4bew YK4StO4XvfdYzFeWWCXlX7tI3BBCP5FaroXvnxQo5oz/DtKHkAXWJX6KPq4ujgGdO2KrYS 9twPPBqCcIN1tCfx8ZZcL16IV8aL2tzlguL+pUwtJiVWyrUpUSrMQT49WuoBrUgqJOfIED FDopYgfR97BDcphz+B9Ap8gozi2TV2eBQiEDRpGpMNucnwNCQEuxZFafaM/84A== From: Herve Codina To: David Gibson , Rob Herring , Krzysztof Kozlowski , Conor Dooley Cc: Laurent Pinchart , David Lechner , Ayush Singh , Geert Uytterhoeven , devicetree-compiler@vger.kernel.org, devicetree@vger.kernel.org, linux-kernel@vger.kernel.org, devicetree-spec@vger.kernel.org, Hui Pu , Ian Ray , Luca Ceresoli , Thomas Petazzoni , Herve Codina , Frank Li Subject: [PATCH v3 09/15] libfdt: Handle unknown tags in fdt_next_tag() Date: Wed, 26 Aug 2026 10:31:40 +0200 Message-ID: <20260826083146.304291-10-herve.codina@bootlin.com> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260826083146.304291-1-herve.codina@bootlin.com> References: <20260826083146.304291-1-herve.codina@bootlin.com> Precedence: bulk X-Mailing-List: devicetree-compiler@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Last-TLS-Session-Version: TLSv1.3 The structured tag value definition introduced recently gives the ability to ignore unknown tags without any error when they are read. libfdt uses fdt_next_tag() to get a tag. Filtering out tags that should be ignored in fdt_next_tag() allows to have the filtering done globally and allows, in future releases, to have a central place to add new known tags that should not be filtered out. An already known tag exists with the meaning of "just ignore". This tag is FDT_NOP. fdt_next_tag() callers already handle the FDT_NOP tag. Avoid unneeded modification at callers side and use a fake FDT_NOP tag when an unknown tag that should be ignored is encountered. Add also fdt_next_tag_() internal function for callers who need to know if the FDT_NOP tag returned is a real FDT_NOP or a fake FDT_NOP due to an unknown tag. Signed-off-by: Herve Codina Reviewed-by: Luca Ceresoli Reviewed-by: Frank Li --- libfdt/fdt.c | 75 ++++++++++++++++++++++++++++++++++++++-- libfdt/libfdt_internal.h | 3 ++ tests/run_tests.sh | 9 +++-- 3 files changed, 83 insertions(+), 4 deletions(-) diff --git a/libfdt/fdt.c b/libfdt/fdt.c index eb803e8a..506e0dd3 100644 --- a/libfdt/fdt.c +++ b/libfdt/fdt.c @@ -167,7 +167,7 @@ const void *fdt_offset_ptr(const void *fdt, int offset, unsigned int len) return fdt_offset_ptr_(fdt, offset); } -uint32_t fdt_next_tag(const void *fdt, int startoffset, int *nextoffset) +static uint32_t fdt_next_tag_all(const void *fdt, int startoffset, int *nextoffset) { const fdt32_t *tagp, *lenp; uint32_t tag, len, sum; @@ -218,7 +218,37 @@ uint32_t fdt_next_tag(const void *fdt, int startoffset, int *nextoffset) break; default: - return FDT_END; + if (!(tag & FDT_TAG_STRUCTURED) || !(tag & FDT_TAG_SKIP_SAFE)) + return FDT_END; + + switch (tag & FDT_TAG_DATA_MASK) { + case FDT_TAG_DATA_NONE: + break; + case FDT_TAG_DATA_1CELL: + offset += FDT_CELLSIZE; + break; + case FDT_TAG_DATA_2CELLS: + offset += 2 * FDT_CELLSIZE; + break; + case FDT_TAG_DATA_VARLEN: + /* Get the length */ + lenp = fdt_offset_ptr(fdt, offset, sizeof(*lenp)); + if (!can_assume(VALID_DTB) && !lenp) + return FDT_END; /* premature end */ + len = fdt32_to_cpu(*lenp); + /* + * Skip the cell encoding the length and the + * following length bytes + */ + len += sizeof(*lenp); + sum = len + offset; + if (!can_assume(VALID_DTB) && + (sum >= INT_MAX || sum < (uint32_t) offset)) + return FDT_END; /* premature end */ + + offset += len; + break; + } } if (!fdt_offset_ptr(fdt, startoffset, offset - startoffset)) @@ -228,6 +258,47 @@ uint32_t fdt_next_tag(const void *fdt, int startoffset, int *nextoffset) return tag; } +static bool fdt_tag_is_unknown(uint32_t tag) +{ + switch (tag) { + case FDT_BEGIN_NODE: + case FDT_END_NODE: + case FDT_PROP: + case FDT_NOP: + case FDT_END: + return false; + default: + break; + } + return true; +} + +uint32_t fdt_next_tag_(const void *fdt, int startoffset, int *nextoffset, bool *is_unknown) +{ + uint32_t tag; + bool unknown = false; + + /* Retrieve next tag */ + tag = fdt_next_tag_all(fdt, startoffset, nextoffset); + if (tag == FDT_END) + goto end; + + if (fdt_tag_is_unknown(tag)) { + unknown = true; + /* Use a known tag that should be skipped by the caller */ + tag = FDT_NOP; + } +end: + if (is_unknown) + *is_unknown = unknown; + return tag; +} + +uint32_t fdt_next_tag(const void *fdt, int startoffset, int *nextoffset) +{ + return fdt_next_tag_(fdt, startoffset, nextoffset, NULL); +} + int fdt_check_node_offset_(const void *fdt, int offset) { if (!can_assume(VALID_INPUT) diff --git a/libfdt/libfdt_internal.h b/libfdt/libfdt_internal.h index 0e103caf..f2e30ce8 100644 --- a/libfdt/libfdt_internal.h +++ b/libfdt/libfdt_internal.h @@ -20,6 +20,9 @@ int32_t fdt_ro_probe_(const void *fdt); } \ } +uint32_t fdt_next_tag_(const void *fdt, int startoffset, int *nextoffset, + bool *is_unknown); + int fdt_check_node_offset_(const void *fdt, int offset); int fdt_check_prop_offset_(const void *fdt, int offset); diff --git a/tests/run_tests.sh b/tests/run_tests.sh index 8fc23cb7..225c22f8 100755 --- a/tests/run_tests.sh +++ b/tests/run_tests.sh @@ -577,11 +577,12 @@ libfdt_tests () { run_test dtbs_equal_ordered cell-overflow.test.dtb cell-overflow-results.test.dtb # check full tests - for good in test_tree1.dtb; do + for good in test_tree1.dtb unknown_tags_can_skip.dtb; do run_test check_full $good done for bad in truncated_property.dtb truncated_string.dtb \ - truncated_memrsv.dtb two_roots.dtb named_root.dtb; do + truncated_memrsv.dtb two_roots.dtb named_root.dtb \ + unknown_tags_no_skip.dtb; do run_test check_full -n $bad done } @@ -962,6 +963,10 @@ fdtget_tests () { run_fdtget_test "" -tx \ -d "" $dtb /randomnode doctor-who run_fdtget_test "" -tx -d "" $dtb /memory doctor-who + + # test with unknown tags involved + run_fdtget_test "25601 25602" unknown_tags_can_skip.dtb /subnode1 prop-int + run_wrap_error_test $DTGET unknown_tags_no_skip.dtb /subnode1 prop-int } fdtput_tests () { -- 2.55.0