[PATCH 2/4] NET: NETROM: When adding a route verify length of mnemonic string.

[Ralf Baechle <ralf@xxxxxxxxxxxxxx>]

struct nr_route_struct's mnemonic permits a string of up to 7 bytes to be
used.  If userland passes a not zero terminated string to the kernel adding
a node to the routing table might result in the kernel attempting to read
copy a too long string.

Mnemonic is part of the NET/ROM routing protocol; NET/ROM routing table
updates only broadcast 6 bytes.  The 7th byte in the mnemonic array exists
only as a \0 termination character for the kernel code's convenience.

Fixed by rejecting mnemonic strings that have no terminating \0 in the first
7 characters.  Do this test only NETROM_NODE to avoid breaking NETROM_NEIGH
where userland might passing an uninitialized mnemonic field.

Initial patch by Dan Carpenter <dan.carpenter@xxxxxxxxxx>.

Signed-off-by: Ralf Baechle <ralf@xxxxxxxxxxxxxx>
Cc: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
Cc: Walter Harms <wharms@xxxxxx>
Cc: Thomas Osterried <thomas@xxxxxxxxxxxx>
---
 net/netrom/nr_route.c |    5 +++++
 1 files changed, 5 insertions(+), 0 deletions(-)

diff --git a/net/netrom/nr_route.c b/net/netrom/nr_route.c
index 915a87b..8d7716c 100644
--- a/net/netrom/nr_route.c
+++ b/net/netrom/nr_route.c
@@ -678,6 +678,11 @@ int nr_rt_ioctl(unsigned int cmd, void __user *arg)
 		}
 		switch (nr_route.type) {
 		case NETROM_NODE:
+			if (strnlen(nr_route.mnemonic, 7) == 7) {
+				ret = -EINVAL;
+				break;
+			}
+
 			ret = nr_add_node(&nr_route.callsign,
 				nr_route.mnemonic,
 				&nr_route.neighbour,
-- 
1.7.4.4


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