GPF in process_one_work (flush_to_ldisc)

[Dmitry Vyukov]

Hello,

The following program triggers GPF:


// autogenerated by syzkaller (http://github.com/google/syzkaller)
#include <syscall.h>
#include <string.h>
#include <stdint.h>

int main()
{
long r0 = syscall(SYS_mmap, 0x20000000ul, 0x10000ul, 0x3ul,
0x32ul, 0xfffffffffffffffful, 0x0ul);
long r1 = syscall(SYS_pipe2, 0x20000000ul, 0x80000ul, 0, 0, 0, 0);
long r2 = -1;
if (r1 != -1)
r2 = *(uint32_t*)0x20000000;
long r3 = -1;
if (r1 != -1)
r3 = *(uint32_t*)0x20000004;
long r6 = syscall(SYS_open, "/dev/ptmx", 0x1ul, 0x0ul, 0, 0, 0);
long r10 = syscall(SYS_write, r6, 0x20001000ul, 0x1000ul, 0, 0, 0);
*(uint32_t*)0x20003000 = 0x17;
long r12 = syscall(SYS_ioctl, r6, 0x5423ul, 0x20003000ul, 0, 0, 0);
long r18 = syscall(SYS_mmap, 0x20002000ul, 0x1000ul, 0x3ul,
0x32ul, r2, 0x0ul);
long r20 = syscall(SYS_mmap, 0x20002000ul, 0x1000ul, 0x3ul,
0x32ul, 0xfffffffffffffffful, 0x0ul);
*(uint64_t*)0x20002000 = 0x2000225e;
*(uint64_t*)0x20002008 = 0x56;
*(uint64_t*)0x20002010 = 0x20002bc6;
*(uint64_t*)0x20002018 = 0xe7;
*(uint64_t*)0x20002020 = 0x20002fd7;
*(uint64_t*)0x20002028 = 0x29;
*(uint64_t*)0x20002030 = 0x20002f39;
*(uint64_t*)0x20002038 = 0xc7;
long r33 = syscall(SYS_writev, r3, 0x20002000ul, 0x4ul, 0, 0, 0);
long r34 = syscall(SYS_dup2, r2, r6, 0, 0, 0, 0);
return 0;
}



BUG: unable to handle kernel NULL pointer dereference at (null)
IP: [< (null)>] (null)
PGD 3752d067 PUD 37a7b067 PMD 0
Oops: 0010 [#1] SMP KASAN
Modules linked in:
CPU: 2 PID: 148 Comm: kworker/u10:2 Not tainted 4.4.0-rc2+ #51
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
Workqueue: events_unbound flush_to_ldisc
task: ffff88006da94440 ti: ffff88006db60000 task.ti: ffff88006db60000
RIP: 0010:[<0000000000000000>] [< (null)>] (null)
RSP: 0018:ffff88006db67b50 EFLAGS: 00010246
RAX: 0000000000000102 RBX: ffff88003ab32f88 RCX: 0000000000000102
RDX: 0000000000000000 RSI: ffff88003ab330a6 RDI: ffff88003aabd388
RBP: ffff88006db67c48 R08: ffff88003ab32f9c R09: ffff88003ab31fb0
R10: ffff88003ab32fa8 R11: 0000000000000000 R12: dffffc0000000000
R13: ffff88006db67c20 R14: ffffffff863df820 R15: ffff88003ab31fb8
FS: 0000000000000000(0000) GS:ffff88006dc00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b
CR2: 0000000000000000 CR3: 0000000037938000 CR4: 00000000000006e0
Stack:
ffffffff829f46f1 ffff88006da94bf8 ffff88006da94bf8 0000000000000000
ffff88003ab31fb0 ffff88003aabd438 ffff88003ab31ff8 ffff88006430fd90
ffff88003ab32f9c ffffed0007557a87 1ffff1000db6cf78 ffff88003ab32078
Call Trace:
[<ffffffff8127cf91>] process_one_work+0x8f1/0x17a0 kernel/workqueue.c:2030
[<ffffffff8127df14>] worker_thread+0xd4/0x1180 kernel/workqueue.c:2162
[<ffffffff8128faaf>] kthread+0x1cf/0x270 drivers/block/aoe/aoecmd.c:1302
[<ffffffff852a7c2f>] ret_from_fork+0x3f/0x70 arch/x86/entry/entry_64.S:468
Code: Bad RIP value.
RIP [< (null)>] (null)
RSP <ffff88006db67b50>
CR2: 0000000000000000
---[ end trace a587f8947e54d6ea ]---


strace output:

execve("./a.out", ["./a.out"], [/* 14 vars */]) = 0
brk(0) = 0x1590000
brk(0x15911c0) = 0x15911c0
arch_prctl(ARCH_SET_FS, 0x1590880) = 0
readlink("/proc/self/exe", "/root/a.out", 4096) = 11
brk(0x15b21c0) = 0x15b21c0
brk(0x15b3000) = 0x15b3000
access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory)
mmap(0x20000000, 65536, PROT_READ|PROT_WRITE,
MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x20000000
pipe2([3, 4], O_CLOEXEC) = 0
open("/dev/ptmx", O_WRONLY) = 5
write(5, "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"...,
4096) = 4096
ioctl(5, TIOCSETD, [23]) = 0
mmap(0x20002000, 4096, PROT_READ|PROT_WRITE,
MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, 3, 0) = 0x20002000
mmap(0x20002000, 4096, PROT_READ|PROT_WRITE,
MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x20002000
writev(4, [{"\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"...,
86}, {"\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"...,
231}, {"\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"...,
41}, {"\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"...,
199}], 4) = 557
dup2(3, 5

at this point VM hangs.

On commit 6ffeba9607343f15303a399bc402a538800d89d9 (Now 24).

[Peter Hurley]

+ James Freyensee (author of N_TRACESINK line discipline)

On 11/26/2015 09:17 AM, Dmitry Vyukov wrote:
> Hello,
>
> The following program triggers GPF:

Thanks for the report, Dmitry.
Patch attached should fix the GPF.

The GPF happens because the N_TRACESINK line discipline does not
define a receive_buf() method, so the function ptr is NULL.
I audited every ldisc method invocation in case there were other similar
lurking GPFs, but every other method is first checked for NULL.

Thanks again.

Regards,
Peter Hurley

--- >% ---
Subject: [PATCH] tty: Fix GPF in flush_to_ldisc()

A line discipline which does not define a receive_buf() method can
can cause a GPF if data is ever received [1]. Oddly, this was known
to the author of N_TRACESINK in 2011, but never fixed.

[1] GPF report

Reported-by: Dmitry Vyukov <dvy...@google.com>
Signed-off-by: Peter Hurley <pe...@hurleysoftware.com>
---
drivers/tty/tty_buffer.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/tty/tty_buffer.c b/drivers/tty/tty_buffer.c
index 9a479e6..3cd31e0 100644
--- a/drivers/tty/tty_buffer.c
+++ b/drivers/tty/tty_buffer.c
@@ -450,7 +450,7 @@ receive_buf(struct tty_struct *tty, struct tty_buffer *head, int count)
count = disc->ops->receive_buf2(tty, p, f, count);
else {
count = min_t(int, count, tty->receive_room);
- if (count)
+ if (count && disc->ops->receive_buf)
disc->ops->receive_buf(tty, p, f, count);
}
return count;
--
2.6.3