[PATCH net v4] nfc: llcp: fix slab-out-of-bounds reads when logging service names

[Ömer Mete Kaya]

nfc_llcp_wks_sap() and nfc_llcp_build_sdreq_tlv() pass non-null-
terminated strings to pr_debug() using the %s format specifier.
The buffers are allocated via kmemdup() or come from netlink
attributes and are not guaranteed to be null-terminated, causing
__dynamic_pr_debug() to read beyond the allocated region:

  KASAN: slab-out-of-bounds Read in __dynamic_pr_debug

Fix both call sites by using %.*s with the explicit length to limit
the output to the actual length of the string.

Fixes: d9b8d8e19b07 ("NFC: llcp: Service Name Lookup netlink interface")
Reported-by: syzbot+1e3df0852e82c21ca418@xxxxxxxxxxxxxxxxxxxxxxxxx
Closes: https://syzkaller.appspot.com/bug?extid=1e3df0852e82c21ca418
Signed-off-by: Ömer Mete Kaya <omermetekaya0@xxxxxxxxx>
---
v4: Fix missing uri_len argument in pr_debug() format string
    (compile error reported by Simon Horman).
    Add Fixes: d9b8d8e19b07 ("NFC: llcp: Service Name Lookup netlink interface").
 net/nfc/llcp_commands.c | 2 +-
 net/nfc/llcp_core.c     | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/nfc/llcp_commands.c b/net/nfc/llcp_commands.c
index ca89fe967d6a..80a00938c869 100644
--- a/net/nfc/llcp_commands.c
+++ b/net/nfc/llcp_commands.c
@@ -135,7 +135,7 @@ struct nfc_llcp_sdp_tlv *nfc_llcp_build_sdreq_tlv(u8 tid, const char *uri,
 {
 	struct nfc_llcp_sdp_tlv *sdreq;
 
-	pr_debug("uri: %s, len: %zu\n", uri, uri_len);
+	pr_debug("uri: %.*s, len: %zu\n", (int)uri_len, uri, uri_len);
 
 	/* sdreq->tlv_len is u8, takes uri_len, + 3 for header, + 1 for NULL */
 	if (WARN_ON_ONCE(uri_len > U8_MAX - 4))
diff --git a/net/nfc/llcp_core.c b/net/nfc/llcp_core.c
index cac1b5487064..fda236e4d9fd 100644
--- a/net/nfc/llcp_core.c
+++ b/net/nfc/llcp_core.c
@@ -341,7 +341,7 @@ static int nfc_llcp_wks_sap(const char *service_name, size_t service_name_len)
 {
 	int sap, num_wks;
 
-	pr_debug("%s\n", service_name);
+	pr_debug("%.*s\n", (int)service_name_len, service_name);
 
 	if (service_name == NULL)
 		return -EINVAL;
-- 
2.55.0