Re: [PATCH] Bluetooth: L2CAP: Fix memory leak in vhci_write

[Hawkins Jiawei]

On Tue, 18 Oct 2022 at 04:01, Luiz Augusto von Dentz <luiz.dentz@xxxxxxxxx> wrote:
>
> Hi Hawkins,
>
> On Mon, Oct 17, 2022 at 12:47 AM Hawkins Jiawei <yin31149@xxxxxxxxx> wrote:
> >
> > Syzkaller reports a memory leak as follows:
> > ====================================
> > BUG: memory leak
> > unreferenced object 0xffff88810d81ac00 (size 240):
> >   [...]
> >   hex dump (first 32 bytes):
> >     00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
> >     00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
> >   backtrace:
> >     [<ffffffff838733d9>] __alloc_skb+0x1f9/0x270 net/core/skbuff.c:418
> >     [<ffffffff833f742f>] alloc_skb include/linux/skbuff.h:1257 [inline]
> >     [<ffffffff833f742f>] bt_skb_alloc include/net/bluetooth/bluetooth.h:469 [inline]
> >     [<ffffffff833f742f>] vhci_get_user drivers/bluetooth/hci_vhci.c:391 [inline]
> >     [<ffffffff833f742f>] vhci_write+0x5f/0x230 drivers/bluetooth/hci_vhci.c:511
> >     [<ffffffff815e398d>] call_write_iter include/linux/fs.h:2192 [inline]
> >     [<ffffffff815e398d>] new_sync_write fs/read_write.c:491 [inline]
> >     [<ffffffff815e398d>] vfs_write+0x42d/0x540 fs/read_write.c:578
> >     [<ffffffff815e3cdd>] ksys_write+0x9d/0x160 fs/read_write.c:631
> >     [<ffffffff845e0645>] do_syscall_x64 arch/x86/entry/common.c:50 [inline]
> >     [<ffffffff845e0645>] do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
> >     [<ffffffff84600087>] entry_SYSCALL_64_after_hwframe+0x63/0xcd
> > ====================================
> >
> > HCI core will uses hci_rx_work() to process frame, which is queued to
> > the hdev->rx_q tail in hci_recv_frame() by HCI driver.
> >
> > Yet the problem is that, HCI core does not free the skb after handling
> > ACL data packets. To be more specific, when start fragment does not
> > contain the L2CAP length, HCI core just reads possible bytes and
> > finishes frame process in l2cap_recv_acldata(), without freeing the skb,
> > which triggers the above memory leak.
> >
> > This patch solves it by releasing the relative skb, after processing the
> > above case in l2cap_recv_acldata()
> >
> > Fixes: 4d7ea8ee90e4 ("Bluetooth: L2CAP: Fix handling fragmented length")
> > Link: https://lore.kernel.org/all/0000000000000d0b1905e6aaef64@xxxxxxxxxx/
> > Reported-and-tested-by: syzbot+8f819e36e01022991cfa@xxxxxxxxxxxxxxxxxxxxxxxxx
> > Signed-off-by: Hawkins Jiawei <yin31149@xxxxxxxxx>
> > ---
> >  net/bluetooth/l2cap_core.c | 7 +++----
> >  1 file changed, 3 insertions(+), 4 deletions(-)
> >
> > diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c
> > index 1f34b82ca0ec..e0a00854c02e 100644
> > --- a/net/bluetooth/l2cap_core.c
> > +++ b/net/bluetooth/l2cap_core.c
> > @@ -8426,9 +8426,8 @@ void l2cap_recv_acldata(struct hci_conn *hcon, struct sk_buff *skb, u16 flags)
> >                  * expected length.
> >                  */
> >                 if (skb->len < L2CAP_LEN_SIZE) {
> > -                       if (l2cap_recv_frag(conn, skb, conn->mtu) < 0)
> > -                               goto drop;
> > -                       return;
> > +                       l2cap_recv_frag(conn, skb, conn->mtu);
> > +                       goto drop;
>
> Let us use break; instead of goto drop since we have copied the skb into rx_sbk.
Thanks for your suggestion. I will refactor this patch as you suggested.

>
> >                 }
> >
> >                 len = get_unaligned_le16(skb->data) + L2CAP_HDR_SIZE;
> > @@ -8472,7 +8471,7 @@ void l2cap_recv_acldata(struct hci_conn *hcon, struct sk_buff *skb, u16 flags)
> >
> >                         /* Header still could not be read just continue */
> >                         if (conn->rx_skb->len < L2CAP_LEN_SIZE)
> > -                               return;
> > +                               goto drop;
> >                 }
> >
> >                 if (skb->len > conn->rx_len) {
> > --
> > 2.25.1
> >
>
>
> --
> Luiz Augusto von Dentz