| Message ID | 20171009134739.19046-1-phil@nwl.cc |
|---|---|
| State | Accepted |
| Delegated to: | Pablo Neira |
| Headers | show |
| Series | [iptables] extensions: libxt_tcpmss: Detect invalid ranges | expand |
On Mon, Oct 09, 2017 at 03:47:39PM +0200, Phil Sutter wrote: > Previously, an MSS range of e.g. 65535:1000 was silently accepted but > would then never match a packet since the kernel checks whether the MSS > value is greater than or equal to the first *and* less than or equal to > the second value. > > Detect this as a parameter problem and update the man page accordingly. Applied, thanks Phil. -- To unsubscribe from this list: send the line "unsubscribe netfilter-devel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/extensions/libxt_tcpmss.c b/extensions/libxt_tcpmss.c index c7c5971716294..bcd357aa3d8e2 100644 --- a/extensions/libxt_tcpmss.c +++ b/extensions/libxt_tcpmss.c @@ -27,8 +27,12 @@ static void tcpmss_parse(struct xt_option_call *cb) xtables_option_parse(cb); mssinfo->mss_min = cb->val.u16_range[0]; mssinfo->mss_max = mssinfo->mss_min; - if (cb->nvals == 2) + if (cb->nvals == 2) { mssinfo->mss_max = cb->val.u16_range[1]; + if (mssinfo->mss_max < mssinfo->mss_min) + xtables_error(PARAMETER_PROBLEM, + "tcpmss: invalid range given"); + } if (cb->invert) mssinfo->invert = 1; } diff --git a/extensions/libxt_tcpmss.man b/extensions/libxt_tcpmss.man index 8ee715cdbfb07..8253c363418f8 100644 --- a/extensions/libxt_tcpmss.man +++ b/extensions/libxt_tcpmss.man @@ -1,4 +1,4 @@ This matches the TCP MSS (maximum segment size) field of the TCP header. You can only use this on TCP SYN or SYN/ACK packets, since the MSS is only negotiated during the TCP handshake at connection startup time. .TP [\fB!\fP] \fB\-\-mss\fP \fIvalue\fP[\fB:\fP\fIvalue\fP] -Match a given TCP MSS value or range. +Match a given TCP MSS value or range. If a range is given, the second \fIvalue\fP must be greater than or equal to the first \fIvalue\fP.
Previously, an MSS range of e.g. 65535:1000 was silently accepted but would then never match a packet since the kernel checks whether the MSS value is greater than or equal to the first *and* less than or equal to the second value. Detect this as a parameter problem and update the man page accordingly. Signed-off-by: Phil Sutter <phil@nwl.cc> --- extensions/libxt_tcpmss.c | 6 +++++- extensions/libxt_tcpmss.man | 2 +- 2 files changed, 6 insertions(+), 2 deletions(-)