From: Jens Axboe <axboe@xxxxxxxxx>
commit fd7276189450110ed835eb0a334e62d2f1c4e3be upstream.
powerpc sets up PF_KTHREAD and PF_IO_WORKER with a NULL pt_regs, which
from my (arguably very short) checking is not commonly done for other
archs. This is fine, except when PF_IO_WORKER's have been created and
the task does something that causes a coredump to be generated. Then we
get this crash:
Kernel attempted to read user page (160) - exploit attempt? (uid: 1000)
BUG: Kernel NULL pointer dereference on read at 0x00000160
Faulting instruction address: 0xc0000000000c3a60
Oops: Kernel access of bad area, sig: 11 [#1]
LE PAGE_SIZE=64K MMU=Radix SMP NR_CPUS=32 NUMA pSeries
Modules linked in: bochs drm_vram_helper drm_kms_helper xts binfmt_misc ecb ctr syscopyarea sysfillrect cbc sysimgblt drm_ttm_helper aes_generic ttm sg libaes evdev joydev virtio_balloon vmx_crypto gf128mul drm dm_mod fuse loop configfs drm_panel_orientation_quirks ip_tables x_tables autofs4 hid_generic usbhid hid xhci_pci xhci_hcd usbcore usb_common sd_mod
CPU: 1 PID: 1982 Comm: ppc-crash Not tainted 6.3.0-rc2+ #88
Hardware name: IBM pSeries (emulated by qemu) POWER9 (raw) 0x4e1202 0xf000005 of:SLOF,HEAD hv:linux,kvm pSeries
NIP: c0000000000c3a60 LR: c000000000039944 CTR: c0000000000398e0
REGS: c0000000041833b0 TRAP: 0300 Not tainted (6.3.0-rc2+)
MSR: 800000000280b033 <SF,VEC,VSX,EE,FP,ME,IR,DR,RI,LE> CR: 88082828 XER: 200400f8
...
NIP memcpy_power7+0x200/0x7d0
LR ppr_get+0x64/0xb0
Call Trace:
ppr_get+0x40/0xb0 (unreliable)
__regset_get+0x180/0x1f0
regset_get_alloc+0x64/0x90
elf_core_dump+0xb98/0x1b60
do_coredump+0x1c34/0x24a0
get_signal+0x71c/0x1410
do_notify_resume+0x140/0x6f0
interrupt_exit_user_prepare_main+0x29c/0x320
interrupt_exit_user_prepare+0x6c/0xa0
interrupt_return_srr_user+0x8/0x138
Because ppr_get() is trying to copy from a PF_IO_WORKER with a NULL
pt_regs.
Check for a valid pt_regs in both ppc_get/ppr_set, and return an error
if not set. The actual error value doesn't seem to be important here, so
just pick -EINVAL.
Fixes: fa439810cc1b ("powerpc/ptrace: Enable support for NT_PPPC_TAR, NT_PPC_PPR, NT_PPC_DSCR")
Cc: stable@xxxxxxxxxxxxxxx # v4.8+
Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
[mpe: Trim oops in change log, add Fixes & Cc stable]
Signed-off-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Link: https://msgid.link/d9f63344-fe7c-56ae-b420-4a1a04a2ae4c@xxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/powerpc/kernel/ptrace/ptrace-view.c | 6 ++++++
1 file changed, 6 insertions(+)
--- a/arch/powerpc/kernel/ptrace/ptrace-view.c
+++ b/arch/powerpc/kernel/ptrace/ptrace-view.c
@@ -290,6 +290,9 @@ static int gpr_set(struct task_struct *t
static int ppr_get(struct task_struct *target, const struct user_regset *regset,
struct membuf to)
{
+ if (!target->thread.regs)
+ return -EINVAL;
+
return membuf_write(&to, &target->thread.regs->ppr, sizeof(u64));
}
@@ -297,6 +300,9 @@ static int ppr_set(struct task_struct *t
unsigned int pos, unsigned int count, const void *kbuf,
const void __user *ubuf)
{
+ if (!target->thread.regs)
+ return -EINVAL;
+
return user_regset_copyin(&pos, &count, &kbuf, &ubuf,
&target->thread.regs->ppr, 0, sizeof(u64));
}
