On 11/22/2011 08:25 PM, Xi Wang wrote: > The previous commit 30c2235c is incomplete and cannot prevent integer > overflows. For example, when key_len is 0x80000000 (INT_MAX + 1), the > left-hand side of the check, (INT_MAX - key_len), which is unsigned, > becomes 0xffffffff (UINT_MAX) and bypasses the check. > > Signed-off-by: Xi Wang <xi.wang@xxxxxxxxx> > --- > net/sctp/auth.c | 2 +- > 1 files changed, 1 insertions(+), 1 deletions(-) > > diff --git a/net/sctp/auth.c b/net/sctp/auth.c > index 865e68f..989e0fd 100644 > --- a/net/sctp/auth.c > +++ b/net/sctp/auth.c > @@ -82,7 +82,7 @@ static struct sctp_auth_bytes *sctp_auth_create_key(__u32 key_len, gfp_t gfp) > struct sctp_auth_bytes *key; > > /* Verify that we are not going to overflow INT_MAX */ > - if ((INT_MAX - key_len) < sizeof(struct sctp_auth_bytes)) > + if (key_len > INT_MAX - sizeof(struct sctp_auth_bytes)) > return NULL; > > /* Allocate the shared key */ Hmm. Yes, this is a more correct check. Acked-by: Vlad Yasevich <vladislav.yasevich@xxxxxx> However, I don't think this is a security issue. As I've written before, this function is called from 2 places: 1) setsockopt() code path 2) sctp_auth_asoc_set_secret() code path In case (1), sca_keylength is never going to exceed 65535 since it's bounded by a u16 from the user api. As such, The integer promotion will not impact anything and the malloc() will never overflow. In case (2), sca_keylength is computed based on the key the user provided (MAX_USHORT) and the combination of protocol negotiated data where that combination has a max size of 3 * MAX_USHORT (see sctp_auth_make_key_vector()). So, even this case, our maximum key length can be 4* MAX_USHORT which still will always be below MAX_INT and will not overflow. So, I don't think there is big security consideration here, just a bad check that just happens to always work. -vlad -- To unsubscribe from this list: send the line "unsubscribe linux-sctp" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
