Re: [Libguestfs] [libnbd PATCH] common/utils/vector: Better overflow handling

On Mon, Nov 8, 2021 at 9:56 PM Eric Blake <eblake(a)redhat.com&gt; wrote: > > Check newcap * itemsize for overflow prior to calling realloc, so that > we don't accidentally truncate an existing array. Set errno to ENOMEM > on all failure paths, rather than leaving it indeterminate on > overflow. The patch works by assuming a prerequisite that > v->cap*itemsize is always smaller than size_t. > > Fixes: 985dfa72ae (common/utils/vector.c: Optimize vector append) > --- > > Unless you see problems in this, I'll push this and also port it to > nbdkit. > > common/utils/vector.c | 8 +++++--- > 1 file changed, 5 insertions(+), 3 deletions(-) > > diff --git a/common/utils/vector.c b/common/utils/vector.c > index a4b43ce..c37f0c3 100644 > --- a/common/utils/vector.c > +++ b/common/utils/vector.c > @@ -1,5 +1,5 @@ > /* nbdkit > - * Copyright (C) 2018-2020 Red Hat Inc. > + * Copyright (C) 2018-2021 Red Hat Inc. > * > * Redistribution and use in source and binary forms, with or without > * modification, are permitted provided that the following conditions are > @@ -44,12 +44,14 @@ generic_vector_reserve (struct generic_vector *v, size_t n, size_t itemsize) > size_t reqcap, newcap; > > reqcap = v->cap + n; > - if (reqcap < v->cap) > + if (reqcap * itemsize < v->cap * itemsize) { Just to make sure I understand this correctly: v->cap * itemsize must be valid value since this is the current allocation, computed in a previous call to generic_vector_reserve... > + errno = ENOMEM; > return -1; /* overflow */ > + } > > newcap = (v->cap * 3 + 1) / 2; > > - if (newcap < reqcap) > + if (newcap * itemsize < reqcap * itemsize) So reqcap * itemsize is valid because we passed the check above. > newcap = reqcap; > > newptr = realloc (v->ptr, newcap * itemsize); Looks right to me.