BUG: unable to handle page fault for address = ADDR

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: c392798a Add linux-next specific files for 20190424
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=14772c42a00000
kernel config: https://syzkaller.appspot.com/x/.config?x=37a4076eb047eef5
dashboard link: https://syzkaller.appspot.com/bug?extid=45474c076a4927533d2e
compiler: gcc (GCC) 9.0.0 20181231 (experimental)
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1369c242a00000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=12ee2e88a00000

The bug was bisected to:

commit bcdd0ca8cb8730573afebcaae4138f8f4c8eaa20
Author: Tetsuo Handa <penguin...@I-love.SAKURA.ne.jp>
Date: Wed Apr 25 11:12:31 2018 +0000

tty: Use __GFP_NOFAIL for tty_ldisc_get()

bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=157d9014a00000
final crash: https://syzkaller.appspot.com/x/report.txt?x=177d9014a00000
console output: https://syzkaller.appspot.com/x/log.txt?x=137d9014a00000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+45474c...@syzkaller.appspotmail.com
Fixes: bcdd0ca8cb87 ("tty: Use __GFP_NOFAIL for tty_ldisc_get()")

do_syscall_64+0x103/0x670 arch/x86/entry/common.c:298
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x441149
Code: e8 5c ae 02 00 48 83 c4 18 c3 0f 1f 80 00 00 00 00 48 89 f8 48 89 f7
48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff
ff 0f 83 bb 0a fc ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007fffd8ae1c38 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 0000000000441149
RDX: 0000000020000140 RSI: 0000000000005423 RDI: 0000000000000003
RBP: 00007fffd8ae1c50 R08: 0000000000000001 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: ffffffffffffffff
R13: 0000000000000004 R14: 0000000000000000 R15: 0000000000000000
BUG: unable to handle page fault for address = fffffffffffffff4
#PF: supervisor-privileged read access from kernel code
#PF: error_code(0x0000) - not-present page
PGD 8870067 P4D 8870067 PUD 8872067 PMD 0
Oops: 0000 [#1] PREEMPT SMP KASAN
CPU: 1 PID: 7949 Comm: syz-executor714 Not tainted 5.1.0-rc6-next-20190424
#30
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
RIP: 0010:slhc_free+0x31/0xb0 drivers/net/slip/slhc.c:159
Code: 54 49 89 fc e8 c0 b3 15 fd 4d 85 e4 74 77 e8 b6 b3 15 fd 4c 89 e2 48
b8 00 00 00 00 00 fc ff df 48 c1 ea 03 80 3c 02 00 75 6d <4d> 8b 2c 24 4d
85 ed 74 0d e8 91 b3 15 fd 4c 89 ef e8 09 5b 4e fd
RSP: 0018:ffff8880a3e7f9f0 EFLAGS: 00010246
RAX: dffffc0000000000 RBX: fffffffffffffff4 RCX: 1ffff1101426e1c6
RDX: 1ffffffffffffffe RSI: ffffffff845b7bea RDI: fffffffffffffff4
RBP: ffff8880a3e7fa00 R08: ffff8880a1370540 R09: ffff8880a1370e30
R10: 0000000000000000 R11: 0000000000000000 R12: fffffffffffffff4
R13: ffff88809f531040 R14: 00000000ffffff97 R15: ffff8880a3dff2c0
FS: 0000555556f4d880(0000) GS:ffff8880ae900000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: fffffffffffffff4 CR3: 000000008b56d000 CR4: 00000000001406e0
Call Trace:
sl_alloc_bufs drivers/net/slip/slip.c:196 [inline]
slip_open+0xe16/0x1138 drivers/net/slip/slip.c:821
tty_ldisc_open.isra.0+0x8b/0xe0 drivers/tty/tty_ldisc.c:469
tty_set_ldisc+0x2d7/0x690 drivers/tty/tty_ldisc.c:596
tiocsetd drivers/tty/tty_io.c:2332 [inline]
tty_ioctl+0x5dc/0x15c0 drivers/tty/tty_io.c:2592
vfs_ioctl fs/ioctl.c:46 [inline]
file_ioctl fs/ioctl.c:509 [inline]
do_vfs_ioctl+0xd6e/0x1390 fs/ioctl.c:696
ksys_ioctl+0xab/0xd0 fs/ioctl.c:713
__do_sys_ioctl fs/ioctl.c:720 [inline]
__se_sys_ioctl fs/ioctl.c:718 [inline]
__x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:718
do_syscall_64+0x103/0x670 arch/x86/entry/common.c:298
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x441149
Code: e8 5c ae 02 00 48 83 c4 18 c3 0f 1f 80 00 00 00 00 48 89 f8 48 89 f7
48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff
ff 0f 83 bb 0a fc ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007fffd8ae1c38 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 0000000000441149
RDX: 0000000020000140 RSI: 0000000000005423 RDI: 0000000000000003
RBP: 00007fffd8ae1c50 R08: 0000000000000001 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: ffffffffffffffff
R13: 0000000000000004 R14: 0000000000000000 R15: 0000000000000000
Modules linked in:
CR2: fffffffffffffff4
---[ end trace c314d2d667c67584 ]---
RIP: 0010:slhc_free+0x31/0xb0 drivers/net/slip/slhc.c:159
Code: 54 49 89 fc e8 c0 b3 15 fd 4d 85 e4 74 77 e8 b6 b3 15 fd 4c 89 e2 48
b8 00 00 00 00 00 fc ff df 48 c1 ea 03 80 3c 02 00 75 6d <4d> 8b 2c 24 4d
85 ed 74 0d e8 91 b3 15 fd 4c 89 ef e8 09 5b 4e fd
RSP: 0018:ffff8880a3e7f9f0 EFLAGS: 00010246
RAX: dffffc0000000000 RBX: fffffffffffffff4 RCX: 1ffff1101426e1c6
RDX: 1ffffffffffffffe RSI: ffffffff845b7bea RDI: fffffffffffffff4
RBP: ffff8880a3e7fa00 R08: ffff8880a1370540 R09: ffff8880a1370e30
R10: 0000000000000000 R11: 0000000000000000 R12: fffffffffffffff4
R13: ffff88809f531040 R14: 00000000ffffff97 R15: ffff8880a3dff2c0
FS: 0000555556f4d880(0000) GS:ffff8880ae900000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: fffffffffffffff4 CR3: 000000008b56d000 CR4: 00000000001406e0


---
This bug is generated by a bot. It may contain errors.
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For information about bisection process see: https://goo.gl/tpsmEJ#bisection
syzbot can test patches for this bug, for details see:
https://goo.gl/tpsmEJ#testing-patches

[Linus Torvalds]

On Thu, Apr 25, 2019 at 3:16 PM syzbot
<syzbot+45474c...@syzkaller.appspotmail.com> wrote:
>
> The bug was bisected to:
>
> commit bcdd0ca8cb8730573afebcaae4138f8f4c8eaa20
> Author: Tetsuo Handa <penguin...@I-love.SAKURA.ne.jp>
> Date: Wed Apr 25 11:12:31 2018 +0000
>
> tty: Use __GFP_NOFAIL for tty_ldisc_get()

I think this just makes slhc_init() fail more easily, but the bug was
pre-existing.

The *real* source of the bug seems to be

4ab42d78e37a ("ppp, slip: Validate VJ compression slot parameters
completely")

from back in 2015.

We have (in drivers/net/slip/slip.c: sl_alloc_bufs())

slcomp = slhc_init(16, 16);
if (IS_ERR(slcomp))
goto err_exit;
....
err_exit:
#ifdef SL_INCLUDE_CSLIP
kfree(cbuff);
slhc_free(slcomp);
#endif

so we do "slhc_free()" on an error pointer, which results in

BUG: unable to handle page fault for address = fffffffffffffff4

and the fix might be something like the appended whitespace-damaged
trivial one-liner: just make slhc_free() silently ignore an error
pointer, to match the slhc_init() return behavior.

Ben? David?

Linus

diff --git a/drivers/net/slip/slhc.c b/drivers/net/slip/slhc.c
index f4e93f5fc204..ea90db3c7705 100644
--- a/drivers/net/slip/slhc.c
+++ b/drivers/net/slip/slhc.c
@@ -153,7 +153,7 @@ slhc_init(int rslots, int tslots)
void
slhc_free(struct slcompress *comp)
{
- if ( comp == NULLSLCOMPR )
+ if ( IS_ERR_OR_NULL(comp) )
return;

if ( comp->tstate != NULLSLSTATE )

[Ben Hutchings]

On Thu, 2019-04-25 at 16:13 -0700, Linus Torvalds wrote:
[...]

> so we do "slhc_free()" on an error pointer, which results in
>
> BUG: unable to handle page fault for address = fffffffffffffff4
>
> and the fix might be something like the appended whitespace-damaged
> trivial one-liner: just make slhc_free() silently ignore an error
> pointer, to match the slhc_init() return behavior.
>
> Ben? David?

This looks sensible to me.

Ben.

> Linus
>
> diff --git a/drivers/net/slip/slhc.c b/drivers/net/slip/slhc.c
> index f4e93f5fc204..ea90db3c7705 100644
> --- a/drivers/net/slip/slhc.c
> +++ b/drivers/net/slip/slhc.c
> @@ -153,7 +153,7 @@ slhc_init(int rslots, int tslots)
> void
> slhc_free(struct slcompress *comp)
> {
> - if ( comp == NULLSLCOMPR )
> + if ( IS_ERR_OR_NULL(comp) )
> return;
>
> if ( comp->tstate != NULLSLSTATE )

--
Ben Hutchings
It is impossible to make anything foolproof
because fools are so ingenious.

[Linus Torvalds]

On Fri, Apr 26, 2019 at 4:36 AM Ben Hutchings <b...@decadent.org.uk> wrote:
>
> This looks sensible to me.

I've just applied it directly to my tree. It looks like slip is
largely a thing of the past, there have been no slip-specific patches
for the last year (all changes in the last year have been due to
treewide changes that weren't slip-specific).

Linus