Re: [PATCH] libfdt: fdt_get_alias_namelen: Validate aliases

[David Gibson <david@gibson.dropbear.id.au>]

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On Tue, Oct 10, 2023 at 03:18:04PM +0100, Mike McTernan wrote:
> On Sat, 7 Oct 2023 at 12:07, Pierre-Clément Tosi <ptosi@google.com> wrote:
> >
> > Ensure that the alias found is valid i.e.
> >
> >     An alias value is a device path and is encoded as a string.
> >     The value represents the full path to a node, ...
> >
> > This protects against a stack overflow (fdt_path_offset_namelen() calls
> > fdt_get_alias_namelen() then fdt_path_offset(alias), ...) when /aliases
> > has an empty property with an empty name.
> >
> > Co-developed-by: Mike McTernan <mikemcternan@google.com>
> > Signed-off-by: Pierre-Clément Tosi <ptosi@google.com>
> 
> Acked-by: Mike McTernan <mikemcternan@google.com>

Thanks, I've added this to the patch on merge.

> 
> > ---
> >  libfdt/fdt_ro.c   | 11 ++++++++++-
> >  tests/aliases.dts |  3 +++
> >  tests/get_alias.c | 12 +++++++++++-
> >  3 files changed, 24 insertions(+), 2 deletions(-)
> >
> > diff --git a/libfdt/fdt_ro.c b/libfdt/fdt_ro.c
> > index c4c520c..bda5c0d 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) &&
> > +           !(len > 0 && alias && memchr(alias, '\0', len) && *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..8820974 100644
> > --- a/tests/aliases.dts
> > +++ b/tests/aliases.dts
> > @@ -8,6 +8,9 @@
> >                 s1 = &sub1;
> >                 ss1 = &subsub1;
> >                 sss1 = &subsubsub1;
> > +               badpath = "wrong";
> > +               badpathlong = "wrong/with/parts";
> > +               empty = "";
> >         };
> >
> >         sub1: subnode@1 {
> > diff --git a/tests/get_alias.c b/tests/get_alias.c
> > index fb2c38c..4f3f6fd 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);
> > @@ -36,6 +43,9 @@ int main(int argc, char *argv[])
> >         test_init(argc, argv);
> >         fdt = load_blob_arg(argc, argv);
> >
> > +       check_alias(fdt, NULL, "badpath");
> > +       check_alias(fdt, NULL, "badpathlong");
> > +       check_alias(fdt, NULL, "empty");
> >         check_alias(fdt, "/subnode@1", "s1");
> >         check_alias(fdt, "/subnode@1/subsubnode", "ss1");
> >         check_alias(fdt, "/subnode@1/subsubnode/subsubsubnode", "sss1");
> >
> >
> 

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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