[PATCH net] net: sched: em_text: require NUL-terminated algo name

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

em_text_change() copies the user-supplied tcf_em_text struct from
netlink and passes conf->algo straight to textsearch_prepare(), which
forwards it to lookup_ts_algo() (strcmp) and request_module() (vsnprintf
%s).  But the algo[16] field is never validated to be NULL-terminated,
so a fully populated array reads past it into the adjacent
from_offset/to_offset/pattern_len fields and the trailing pattern bytes
during the string operations.

This type of pattern is properly checked in the string_mt_check() for
xt_string netfilter matching function, but for some reason was not added
here, so fix this up by doing the same exact thing.

Cc: Jamal Hadi Salim <jhs@mojatatu.com>
Cc: Jiri Pirko <jiri@resnulli.us>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: Paolo Abeni <pabeni@redhat.com>
Cc: Simon Horman <horms@kernel.org>
Fixes: d675c989ed2d ("[PKT_SCHED]: Packet classification based on textsearch (ematch)")
Cc: stable <stable@kernel.org>
Assisted-by: gregkh_clanker_t1000
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
Note, my tools flagged this, so I fixed this up the same way that
string_mt_check() did, but if there is some other way that this should
be resolved, or I got this totally wrong that this isn't an issue,
please let me know, thanks!


 net/sched/em_text.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/net/sched/em_text.c b/net/sched/em_text.c
index 343f1aebeec2..24a8aa21971d 100644
--- a/net/sched/em_text.c
+++ b/net/sched/em_text.c
@@ -58,6 +58,9 @@ static int em_text_change(struct net *net, void *data, int len,
 	if (len < sizeof(*conf) || len < (sizeof(*conf) + conf->pattern_len))
 		return -EINVAL;
 
+	if (conf->algo[sizeof(conf->algo) - 1] != '\0')
+		return -EINVAL;
+
 	if (conf->from_layer > conf->to_layer)
 		return -EINVAL;
 
-- 
2.53.0