On 01/04/2016 12:29 PM, James Hogan wrote:
commit 6f06a2c45d8d714ea3b11a360b4a7191e52acaa4 upstream. When EVA is in use, __copy_from_user() was unconditionally using the EVA instructions to read the user address space, however this can also be used for kernel access. If the address isn't a valid user address it will cause an address error or TLB exception, and if it is then user memory may be read instead of kernel memory. For example in the following stack trace from Linux v3.10 (changes since then will prevent this particular one still happening) kernel_sendmsg() set the user address limit to KERNEL_DS, and tcp_sendmsg() goes on to use __copy_from_user() with a kernel address in KSeg0. [<8002d434>] __copy_fromuser_common+0x10c/0x254 [<805710e0>] tcp_sendmsg+0x5f4/0xf00 [<804e8e3c>] sock_sendmsg+0x78/0xa0 [<804e8f28>] kernel_sendmsg+0x24/0x38 [<804ee0f8>] sock_no_sendpage+0x70/0x7c [<8017c820>] pipe_to_sendpage+0x80/0x98 [<8017c6b0>] splice_from_pipe_feed+0xa8/0x198 [<8017cc54>] __splice_from_pipe+0x4c/0x8c [<8017e844>] splice_from_pipe+0x58/0x78 [<8017e884>] generic_splice_sendpage+0x20/0x2c [<8017d690>] do_splice_from+0xb4/0x110 [<8017d710>] direct_splice_actor+0x24/0x30 [<8017d394>] splice_direct_to_actor+0xd8/0x208 [<8017d51c>] do_splice_direct+0x58/0x7c [<8014eaf4>] do_sendfile+0x1dc/0x39c [<8014f82c>] SyS_sendfile+0x90/0xf8 Add the eva_kernel_access() check in __copy_from_user() like the one in copy_from_user().
I think that the best way to fix this problem is - stop skb_do_copy_data_nocache() using __copy_from_user_nocache(). All TCP/IP stuff (beyond SCTP) doesn't use "accelerated" __copy*() functions. Adding a user space check in __copy_from_user() kills the original design. And splitting a user space processing in two places (skb_do_copy_data_nocache() calls access_ok(), BTW) - and it is also a bad thing in my mind.
- Leonid.
