When reiniting a tty we can end up with: [ 417.514499] Unable to handle kernel paging request for data at address 0x00002260 [ 417.515361] Faulting instruction address: 0xc0000000006fad80 cpu 0x15: Vector: 300 (Data Access) at [c00000799411f890] pc: c0000000006fad80: n_tty_receive_buf_common+0xc0/0xbd0 lr: c0000000006fad5c: n_tty_receive_buf_common+0x9c/0xbd0 sp: c00000799411fb10 msr: 900000000280b033 dar: 2260 dsisr: 40000000 current = 0xc0000079675d1e00 paca = 0xc00000000fb0d200 softe: 0 irq_happened: 0x01 pid = 5, comm = kworker/u56:0 Linux version 4.11.0-rc5-next-20170405 (mikey@bml86) (gcc version 5.4.0 20160609 (Ubuntu/IBM 5.4.0-6ubuntu1~16.04.4) ) #2 SMP Thu Apr 6 00:36:46 CDT 2017 enter ? for help [c00000799411fbe0] c0000000006ff968 tty_ldisc_receive_buf+0x48/0xe0 [c00000799411fc10] c0000000007009d8 tty_port_default_receive_buf+0x68/0xe0 [c00000799411fc50] c0000000006ffce4 flush_to_ldisc+0x114/0x130 [c00000799411fca0] c00000000010a0fc process_one_work+0x1ec/0x580 [c00000799411fd30] c00000000010a528 worker_thread+0x98/0x5d0 [c00000799411fdc0] c00000000011343c kthread+0x16c/0x1b0 [c00000799411fe30] c00000000000b4e8 ret_from_kernel_thread+0x5c/0x74
This is due to a NULL ptr dref of tty->disc_data in tty_ldisc_receive_buf() called from flush_to_ldisc() This fixes the issue by moving the disc_data read to after we take the semaphore. Then when disc_data NULL returning 0 data processed rather than dereferencing it. Cc: <sta...@vger.kernel.org> [4.10+] Signed-off-by: Michael Neuling <mi...@neuling.org> --- drivers/tty/n_tty.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c index bdf0e6e899..a2a9832a42 100644 --- a/drivers/tty/n_tty.c +++ b/drivers/tty/n_tty.c @@ -1668,11 +1668,17 @@ static int n_tty_receive_buf_common(struct tty_struct *tty, const unsigned char *cp, char *fp, int count, int flow) { - struct n_tty_data *ldata = tty->disc_data; + struct n_tty_data *ldata; int room, n, rcvd = 0, overflow; down_read(&tty->termios_rwsem); + ldata = tty->disc_data; + if (!ldata) { + up_read(&tty->termios_rwsem); + return 0; + } + while (1) { /* * When PARMRK is set, each input char may take up to 3 chars -- 2.9.3