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

[Luiz Augusto von Dentz]

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.

>                 }
>
>                 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