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libfdt: fdt_get_alias_namelen: Validate aliases

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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 <ptosi@google.com>
Acked-by: Mike McTernan <mikemcternan@google.com>
Message-ID: <20231010092725.63h7c45p2fnmj577@google.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
This commit is contained in:
Pierre-Clément Tosi 2023-10-10 10:27:25 +01:00 • committed by David Gibson
parent 52157f13ef
commit 79b9e326a1
3 changed files with 27 additions and 2 deletions
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11
libfdt/fdt_ro.c
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@ -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)