On Mon, Dec 04, 2023 at 10:22:25AM +0100, Nicolas Dichtel wrote: > Le 02/12/2023 à 21:25, Kees Cook a écrit : > > The return value from nla_len() is never expected to be negative, and can > > never be more than struct nlattr::nla_len (a u16). Adjust the prototype > > on the function. This will let GCC's value range optimization passes > > know that the return can never be negative, and can never be larger than > > u16. As recently discussed[1], this silences the following warning in > > GCC 12+: > > > > net/wireless/nl80211.c: In function 'nl80211_set_cqm_rssi.isra': > > net/wireless/nl80211.c:12892:17: warning: 'memcpy' specified bound 18446744073709551615 exceeds maximum object size 9223372036854775807 [-Wstringop-overflow=] > > 12892 | memcpy(cqm_config->rssi_thresholds, thresholds, > > | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > > 12893 | flex_array_size(cqm_config, rssi_thresholds, > > | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > > 12894 | n_thresholds)); > > | ~~~~~~~~~~~~~~ > > > > A future change would be to clamp the subtraction to make sure it never > > wraps around if nla_len is somehow less than NLA_HDRLEN, which would > > have the additional benefit of being defensive in the face of nlattr > > corruption or logic errors. > > > > Reported-by: kernel test robot <lkp@xxxxxxxxx> > > Closes: https://lore.kernel.org/oe-kbuild-all/202311090752.hWcJWAHL-lkp@xxxxxxxxx/ [1] > > Cc: Jakub Kicinski <kuba@xxxxxxxxxx> > > Cc: "David S. Miller" <davem@xxxxxxxxxxxxx> > > Cc: Eric Dumazet <edumazet@xxxxxxxxxx> > > Cc: Paolo Abeni <pabeni@xxxxxxxxxx> > > Cc: Johannes Berg <johannes@xxxxxxxxxxxxxxxx> > > Cc: Jeff Johnson <quic_jjohnson@xxxxxxxxxxx> > > Cc: Michael Walle <mwalle@xxxxxxxxxx> > > Cc: Max Schulze <max.schulze@xxxxxxxxx> > > Cc: netdev@xxxxxxxxxxxxxxx > > Cc: linux-wireless@xxxxxxxxxxxxxxx > > Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx> > > --- > > v2: > > - do not clamp return value (kuba) > > - adjust NLA_HDRLEN to be u16 also > > v1: https://lore.kernel.org/all/20231130200058.work.520-kees@xxxxxxxxxx/ > > --- > > include/net/netlink.h | 2 +- > > include/uapi/linux/netlink.h | 2 +- > > 2 files changed, 2 insertions(+), 2 deletions(-) > > > > diff --git a/include/net/netlink.h b/include/net/netlink.h > > index 83bdf787aeee..7678a596a86b 100644 > > --- a/include/net/netlink.h > > +++ b/include/net/netlink.h > > @@ -1200,7 +1200,7 @@ static inline void *nla_data(const struct nlattr *nla) > > * nla_len - length of payload > > * @nla: netlink attribute > > */ > > -static inline int nla_len(const struct nlattr *nla) > > +static inline u16 nla_len(const struct nlattr *nla) > > { > > return nla->nla_len - NLA_HDRLEN; > > } > > diff --git a/include/uapi/linux/netlink.h b/include/uapi/linux/netlink.h > > index f87aaf28a649..270feed9fd63 100644 > > --- a/include/uapi/linux/netlink.h > > +++ b/include/uapi/linux/netlink.h > > @@ -247,7 +247,7 @@ struct nlattr { > > > > #define NLA_ALIGNTO 4 > > #define NLA_ALIGN(len) (((len) + NLA_ALIGNTO - 1) & ~(NLA_ALIGNTO - 1)) > > -#define NLA_HDRLEN ((int) NLA_ALIGN(sizeof(struct nlattr))) > > +#define NLA_HDRLEN ((__u16) NLA_ALIGN(sizeof(struct nlattr))) > I wonder if this may break the compilation of some userspace tools with errors > like comparing signed and unsigned values. Should I drop this part, then? -- Kees Cook
