Hi Andrej,
On Wed, Oct 02, 2024 at 04:12:17PM +0200, Andrej Shadura wrote:
> 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_bind and
> rfcomm_sock_getsockopt_old.
Was this found by inspection or is there an actual instance of the same
warning? For what it's worth, I haven't seen a warning from this file in
any of my build tests.
> Change the type of len to size_t in both rfcomm_sock_bind and
> rfcomm_sock_getsockopt_old and replace min_t() with min().
>
> Cc: stable@xxxxxxxxxxxxxxx
> Fixes: 9bf4e919ccad ("Bluetooth: Fix type of len in {l2cap,sco}_sock_getsockopt_old()")
I am not sure that I totally agree with this Fixes tag since I did not
have a warning to fix but I guess it makes sense to help with
backporting.
> 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..c0fe96673b3c 100644
> --- a/net/bluetooth/rfcomm/sock.c
> +++ b/net/bluetooth/rfcomm/sock.c
> @@ -328,14 +328,15 @@ static int rfcomm_sock_bind(struct socket *sock, struct sockaddr *addr, int addr
> {
> struct sockaddr_rc sa;
> struct sock *sk = sock->sk;
> - int len, err = 0;
> + int err = 0;
> + size_t len;
>
> if (!addr || addr_len < offsetofend(struct sockaddr, sa_family) ||
> addr->sa_family != AF_BLUETOOTH)
> return -EINVAL;
>
> memset(&sa, 0, sizeof(sa));
> - len = min_t(unsigned int, sizeof(sa), addr_len);
> + len = min(sizeof(sa), addr_len);
> memcpy(&sa, addr, len);
>
> BT_DBG("sk %p %pMR", sk, &sa.rc_bdaddr);
> @@ -729,7 +730,8 @@ 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 +785,7 @@ 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;
>
> --
> 2.43.0
>
