From 79b9e326a162b15ca5758ee214e350f4f7c038fe Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Pierre-Cl=C3=A9ment=20Tosi?= Date: Tue, 10 Oct 2023 10:27:25 +0100 Subject: [PATCH] libfdt: fdt_get_alias_namelen: Validate aliases MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Ensure that the alias found matches the device tree specification v0.4: Each property of the /aliases node defines an alias. The property name specifies the alias name. The property value specifies the full path to a node in the devicetree. This protects against a stack overflow caused by fdt_path_offset_namelen(fdt, path, namelen) calling fdt_path_offset(fdt, fdt_get_alias_namelen(fdt, path, namelen)) leading to infinite recursion on DTs with "circular" aliases. This fix was originally written by Mike McTernan for Android in [1]. [1]: https://android.googlesource.com/platform/external/dtc/+/9308e7f9772bd226fea9925b1fc4d53c127ed4d5 Signed-off-by: Pierre-Clément Tosi Acked-by: Mike McTernan Message-ID: <20231010092725.63h7c45p2fnmj577@google.com> Signed-off-by: David Gibson --- libfdt/fdt_ro.c | 11 ++++++++++- tests/aliases.dts | 4 ++++ tests/get_alias.c | 14 +++++++++++++- 3 files changed, 27 insertions(+), 2 deletions(-) diff --git a/libfdt/fdt_ro.c b/libfdt/fdt_ro.c index c4c520c..9fe2f49 100644 --- a/libfdt/fdt_ro.c +++ b/libfdt/fdt_ro.c @@ -537,7 +537,16 @@ static const void *fdt_path_getprop_namelen(const void *fdt, const char *path, const char *fdt_get_alias_namelen(const void *fdt, const char *name, int namelen) { - return fdt_path_getprop_namelen(fdt, "/aliases", name, namelen, NULL); + int len; + const char *alias; + + alias = fdt_path_getprop_namelen(fdt, "/aliases", name, namelen, &len); + + if (!can_assume(VALID_DTB) && + !(alias && len > 0 && alias[len - 1] == '\0' && *alias == '/')) + return NULL; + + return alias; } const char *fdt_get_alias(const void *fdt, const char *name) diff --git a/tests/aliases.dts b/tests/aliases.dts index 853479a..03ed675 100644 --- a/tests/aliases.dts +++ b/tests/aliases.dts @@ -5,6 +5,10 @@ #size-cells = <0>; aliases { + empty = ""; + loop = "loop"; + nonull = [626164]; + relative = "s1/subsubnode"; s1 = &sub1; ss1 = &subsub1; sss1 = &subsubsub1; diff --git a/tests/get_alias.c b/tests/get_alias.c index fb2c38c..d2888d6 100644 --- a/tests/get_alias.c +++ b/tests/get_alias.c @@ -21,9 +21,16 @@ static void check_alias(void *fdt, const char *path, const char *alias) aliaspath = fdt_get_alias(fdt, alias); - if (path && !aliaspath) + if (!path && !aliaspath) + return; + + if (!aliaspath) FAIL("fdt_get_alias(%s) failed\n", alias); + if (!path) + FAIL("fdt_get_alias(%s) returned %s instead of NULL", + alias, aliaspath); + if (strcmp(aliaspath, path) != 0) FAIL("fdt_get_alias(%s) returned %s instead of %s\n", alias, aliaspath, path); @@ -36,9 +43,14 @@ int main(int argc, char *argv[]) test_init(argc, argv); fdt = load_blob_arg(argc, argv); + check_alias(fdt, NULL, "empty"); + check_alias(fdt, NULL, "nonull"); + check_alias(fdt, NULL, "relative"); check_alias(fdt, "/subnode@1", "s1"); check_alias(fdt, "/subnode@1/subsubnode", "ss1"); check_alias(fdt, "/subnode@1/subsubnode/subsubsubnode", "sss1"); + check_alias(fdt, NULL, "loop"); // Might trigger a stack overflow + PASS(); }