| Message ID | 20161202005906.GA31170@avx2 |
|---|---|
| State | Accepted, archived |
| Delegated to: | David Miller |
| Headers | show |
From: Alexey Dobriyan <adobriyan@gmail.com> Date: Fri, 2 Dec 2016 03:59:06 +0300 > nla_ok() consists of 3 clauses: > > 1) int rem >= (int)sizeof(struct nlattr) > > 2) u16 nla_len >= sizeof(struct nlattr) > > 3) u16 nla_len <= int rem > > The statement is that clause (1) is redundant. > > What it does is ensuring that "rem" is a positive number, > so that in clause (3) positive number will be compared to positive number > with no problems. > > However, "u16" fully fits into "int" and integers do not change value > when upcasting even to signed type. Negative integers will be rejected > by clause (3) just fine. Small positive integers will be rejected > by transitivity of comparison operator. > > NOTE: all of the above DOES NOT apply to nlmsg_ok() where ->nlmsg_len is > u32(!), so 3 clauses AND A CAST TO INT are necessary. > > Obligatory space savings report: -1.6 KB ... > Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com> Looks fine, applied to net-next, thanks.
--- a/include/net/netlink.h +++ b/include/net/netlink.h @@ -698,8 +698,7 @@ static inline int nla_len(const struct nlattr *nla) */ static inline int nla_ok(const struct nlattr *nla, int remaining) { - return remaining >= (int) sizeof(*nla) && - nla->nla_len >= sizeof(*nla) && + return nla->nla_len >= sizeof(*nla) && nla->nla_len <= remaining; }
nla_ok() consists of 3 clauses: 1) int rem >= (int)sizeof(struct nlattr) 2) u16 nla_len >= sizeof(struct nlattr) 3) u16 nla_len <= int rem The statement is that clause (1) is redundant. What it does is ensuring that "rem" is a positive number, so that in clause (3) positive number will be compared to positive number with no problems. However, "u16" fully fits into "int" and integers do not change value when upcasting even to signed type. Negative integers will be rejected by clause (3) just fine. Small positive integers will be rejected by transitivity of comparison operator. NOTE: all of the above DOES NOT apply to nlmsg_ok() where ->nlmsg_len is u32(!), so 3 clauses AND A CAST TO INT are necessary. Obligatory space savings report: -1.6 KB $ ./scripts/bloat-o-meter ../vmlinux-000* ../vmlinux-001* add/remove: 0/0 grow/shrink: 3/63 up/down: 35/-1692 (-1657) function old new delta validate_scan_freqs 142 155 +13 tcf_em_tree_validate 867 879 +12 dcbnl_ieee_del 328 338 +10 netlbl_cipsov4_add_common.isra 218 215 -3 ... ovs_nla_put_actions 888 806 -82 netlbl_cipsov4_add_std 1648 1566 -82 nl80211_parse_sched_scan 2889 2780 -109 ip_tun_from_nlattr 3086 2945 -141 Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com> --- include/net/netlink.h | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-)