On Sun, Sep 10, 2023 at 09:30:18PM +0100, Jeremy Sowden wrote: > `mnl_nlmsg_ok` and `mnl_attr_ok` both expect a signed buffer length > value, `len`, against which to compare the size of the object expected > to fit into the buffer, because they are intended to validate the length > and it may be negative in the case of malformed messages. Comparing > this signed value against unsigned operands leads to compiler warnings, > so the unsigned operands are cast to `int`. Comparing `len` to the size > of the structure is fine, because the structures are only a few bytes in > size. Comparing it to the length fields of `struct nlmsg` and `struct > nlattr`, however, is problematic, since these fields may hold values > greater than `INT_MAX`, in which case the casts will yield negative > values and result in false positives. > > Instead, assign `len` to an unsigned local variable, check for negative > values first, then use the unsigned local for the other comparisons, and > remove the casts. > > Closes: https://bugzilla.netfilter.org/show_bug.cgi?id=1691 > Signed-off-by: Jeremy Sowden <jeremy@xxxxxxxxxx> > --- > src/attr.c | 9 +++++++-- > src/nlmsg.c | 9 +++++++-- > 2 files changed, 14 insertions(+), 4 deletions(-) > > diff --git a/src/attr.c b/src/attr.c > index bc39df4199e7..48e95019d5e8 100644 > --- a/src/attr.c > +++ b/src/attr.c > @@ -97,9 +97,14 @@ EXPORT_SYMBOL void *mnl_attr_get_payload(const struct nlattr *attr) > */ > EXPORT_SYMBOL bool mnl_attr_ok(const struct nlattr *attr, int len) Maybe turn this into uint32_t ? > { > - return len >= (int)sizeof(struct nlattr) && > + size_t ulen = len; > + > + if (len < 0) > + return 0; > + > + return ulen >= sizeof(struct nlattr) && > attr->nla_len >= sizeof(struct nlattr) && > - (int)attr->nla_len <= len; > + attr->nla_len <= ulen; > } > > /** > diff --git a/src/nlmsg.c b/src/nlmsg.c > index c63450174c67..920cad0e0f46 100644 > --- a/src/nlmsg.c > +++ b/src/nlmsg.c > @@ -152,9 +152,14 @@ EXPORT_SYMBOL void *mnl_nlmsg_get_payload_offset(const struct nlmsghdr *nlh, > */ > EXPORT_SYMBOL bool mnl_nlmsg_ok(const struct nlmsghdr *nlh, int len) > { > - return len >= (int)sizeof(struct nlmsghdr) && > + size_t ulen = len; > + > + if (len < 0) > + return 0; > + > + return ulen >= sizeof(struct nlmsghdr) && > nlh->nlmsg_len >= sizeof(struct nlmsghdr) && > - (int)nlh->nlmsg_len <= len; > + nlh->nlmsg_len <= ulen; > } > > /** > -- > 2.40.1 >
