[PATCH v4] net: caif: fix stack out-of-bounds write in cfctrl_link_setup()

[Kangzheng Gu <xiaoguai0992@gmail.com>]

cfctrl_link_setup() copies the RFM volume name from a received control
packet into linkparam.u.rfm.volume until a '\0' is found. A malformed
packet can omit the terminator and make the copy run past the 20-byte
stack buffer.

Stop copying once the buffer is full and mark the frame as failed by
setting CFCTRL_ERR_BIT so the link setup is rejected.

Fixes: b482cd2053e3 ("net-caif: add CAIF core protocol stack")
Cc: stable@vger.kernel.org
Signed-off-by: Kangzheng Gu <xiaoguai0992@gmail.com>
---
 v4:
 - remove the Reported-by.
 - print a warn message and reject link setup by setting CFCTRL_ERR_BIT.
 - using %zu to adapt the compilation of 32-bit kernel.

 net/caif/cfctrl.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/net/caif/cfctrl.c b/net/caif/cfctrl.c
index c6cc2bfed65d..373ab1dc67a7 100644
--- a/net/caif/cfctrl.c
+++ b/net/caif/cfctrl.c
@@ -416,8 +416,16 @@ static int cfctrl_link_setup(struct cfctrl *cfctrl, struct cfpkt *pkt, u8 cmdrsp
 		cp = (u8 *) linkparam.u.rfm.volume;
 		for (tmp = cfpkt_extr_head_u8(pkt);
 		     cfpkt_more(pkt) && tmp != '\0';
-		     tmp = cfpkt_extr_head_u8(pkt))
+		     tmp = cfpkt_extr_head_u8(pkt)) {
+			if (cp >= (u8 *)linkparam.u.rfm.volume +
+			    sizeof(linkparam.u.rfm.volume) - 1) {
+				pr_warn("Request reject, volume name length exceeds %zu\n",
+					sizeof(linkparam.u.rfm.volume));
+				cmdrsp |= CFCTRL_ERR_BIT;
+				break;
+			}
 			*cp++ = tmp;
+		}
 		*cp = '\0';
 
 		if (CFCTRL_ERR_BIT & cmdrsp)
-- 
2.50.1