[PATCH v2] Bluetooth: Fix type of len in rfcomm_sock_getsockopt{,_old}()

[Andrej Shadura <andrew.shadura@xxxxxxxxxxxxxxx>]

Commit 9bf4e919ccad worked around an issue introduced after an innocuous
optimisation change in LLVM main:

> len is defined as an 'int' because it is assigned from
> '__user int *optlen'. However, it is clamped against the result of
> sizeof(), which has a type of 'size_t' ('unsigned long' for 64-bit
> platforms). This is done with min_t() because min() requires compatible
> types, which results in both len and the result of sizeof() being casted
> to 'unsigned int', meaning len changes signs and the result of sizeof()
> is truncated. From there, len is passed to copy_to_user(), which has a
> third parameter type of 'unsigned long', so it is widened and changes
> signs again. This excessive casting in combination with the KCSAN
> instrumentation causes LLVM to fail to eliminate the __bad_copy_from()
> call, failing the build.

The same issue occurs in rfcomm in functions rfcomm_sock_getsockopt and
rfcomm_sock_getsockopt_old.

Change the type of len to size_t in both rfcomm_sock_getsockopt and
rfcomm_sock_getsockopt_old and replace min_t() with min().

Cc: stable@xxxxxxxxxxxxxxx
Co-authored-by: Aleksei Vetrov <vvvvvv@xxxxxxxxxx>
Improves: 9bf4e919ccad ("Bluetooth: Fix type of len in {l2cap,sco}_sock_getsockopt_old()")
Link: https://github.com/ClangBuiltLinux/linux/issues/2007
Link: https://github.com/llvm/llvm-project/issues/85647
Signed-off-by: Andrej Shadura <andrew.shadura@xxxxxxxxxxxxxxx>
Reviewed-by: Nathan Chancellor <nathan@xxxxxxxxxx>
---
 net/bluetooth/rfcomm/sock.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/net/bluetooth/rfcomm/sock.c b/net/bluetooth/rfcomm/sock.c
index 37d63d768afb..5f9d370e09b1 100644
--- a/net/bluetooth/rfcomm/sock.c
+++ b/net/bluetooth/rfcomm/sock.c
@@ -729,7 +729,8 @@ static int rfcomm_sock_getsockopt_old(struct socket *sock, int optname, char __u
 	struct sock *l2cap_sk;
 	struct l2cap_conn *conn;
 	struct rfcomm_conninfo cinfo;
-	int len, err = 0;
+	int err = 0;
+	size_t len;
 	u32 opt;
 
 	BT_DBG("sk %p", sk);
@@ -783,7 +784,7 @@ static int rfcomm_sock_getsockopt_old(struct socket *sock, int optname, char __u
 		cinfo.hci_handle = conn->hcon->handle;
 		memcpy(cinfo.dev_class, conn->hcon->dev_class, 3);
 
-		len = min_t(unsigned int, len, sizeof(cinfo));
+		len = min(len, sizeof(cinfo));
 		if (copy_to_user(optval, (char *) &cinfo, len))
 			err = -EFAULT;
 
@@ -802,7 +803,8 @@ static int rfcomm_sock_getsockopt(struct socket *sock, int level, int optname, c
 {
 	struct sock *sk = sock->sk;
 	struct bt_security sec;
-	int len, err = 0;
+	int err = 0;
+	size_t len;
 
 	BT_DBG("sk %p", sk);
 
@@ -827,7 +829,7 @@ static int rfcomm_sock_getsockopt(struct socket *sock, int level, int optname, c
 		sec.level = rfcomm_pi(sk)->sec_level;
 		sec.key_size = 0;
 
-		len = min_t(unsigned int, len, sizeof(sec));
+		len = min(len, sizeof(sec));
 		if (copy_to_user(optval, (char *) &sec, len))
 			err = -EFAULT;
 
-- 
2.43.0