From: "Steven Rostedt (VMware)" <[email protected]>
The following commands:
# echo 'read_max u64 size;' > synthetic_events
# echo 'hist:keys=common_pid:count=count:onmax($count).trace(read_max,count)' > events/syscalls/sys_enter_read/trigger
Causes:
BUG: kernel NULL pointer dereference, address: 0000000000000000
#PF: supervisor read access in kernel mode
#PF: error_code(0x0000) - not-present page
PGD 0 P4D 0
Oops: 0000 [#1] PREEMPT SMP
CPU: 4 PID: 1763 Comm: bash Not tainted 5.14.0-rc2-test+ #155
Hardware name: Hewlett-Packard HP Compaq Pro 6300 SFF/339A, BIOS K01
v03.03 07/14/2016
RIP: 0010:strcmp+0xc/0x20
Code: 75 f7 31 c0 0f b6 0c 06 88 0c 02 48 83 c0 01 84 c9 75 f1 4c 89 c0
c3 0f 1f 80 00 00 00 00 31 c0 eb 08 48 83 c0 01 84 d2 74 0f <0f> b6 14 07
3a 14 06 74 ef 19 c0 83 c8 01 c3 31 c0 c3 66 90 48 89
RSP: 0018:ffffb5fdc0963ca8 EFLAGS: 00010246
RAX: 0000000000000000 RBX: ffffffffb3a4e040 RCX: 0000000000000000
RDX: 0000000000000000 RSI: ffff9714c0d0b640 RDI: 0000000000000000
RBP: 0000000000000000 R08: 00000022986b7cde R09: ffffffffb3a4dff8
R10: 0000000000000000 R11: 0000000000000000 R12: ffff9714c50603c8
R13: 0000000000000000 R14: ffff97143fdf9e48 R15: ffff9714c01a2210
FS: 00007f1fa6785740(0000) GS:ffff9714da400000(0000)
knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000000 CR3: 000000002d863004 CR4: 00000000001706e0
Call Trace:
__find_event_file+0x4e/0x80
action_create+0x6b7/0xeb0
? kstrdup+0x44/0x60
event_hist_trigger_func+0x1a07/0x2130
trigger_process_regex+0xbd/0x110
event_trigger_write+0x71/0xd0
vfs_write+0xe9/0x310
ksys_write+0x68/0xe0
do_syscall_64+0x3b/0x90
entry_SYSCALL_64_after_hwframe+0x44/0xae
RIP: 0033:0x7f1fa6879e87
The problem was the "trace(read_max,count)" where the "count" should be
"$count" as "onmax()" only handles variables (although it really should be
able to figure out that "count" is a field of sys_enter_read). But there's
a path that does not find the variable and ends up passing a NULL for the
event, which ends up getting passed to "strcmp()".
Add a check for NULL to return and error on the command with:
# cat error_log
hist:syscalls:sys_enter_read: error: Couldn't create or find variable
Command: hist:keys=common_pid:count=count:onmax($count).trace(read_max,count)
^
Cc: [email protected]
Fixes: 50450603ec9cb tracing: Add 'onmax' hist trigger action support
Signed-off-by: Steven Rostedt (VMware) <[email protected]>
---
kernel/trace/trace_events_hist.c | 2 ++
1 file changed, 2 insertions(+)
diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
index 949ef09dc537..a48aa2a2875b 100644
--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c
@@ -3430,6 +3430,8 @@ trace_action_create_field_var(struct hist_trigger_data *hist_data,
event = data->match_data.event;
}
+ if (!event)
+ goto free;
/*
* At this point, we're looking at a field on another
* event. Because we can't modify a hist trigger on
--
2.31.1
On Sun, 8 Aug 2021 00:30:11 -0400
Steven Rostedt <[email protected]> wrote:
> diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
> index 949ef09dc537..a48aa2a2875b 100644
> --- a/kernel/trace/trace_events_hist.c
> +++ b/kernel/trace/trace_events_hist.c
> @@ -3430,6 +3430,8 @@ trace_action_create_field_var(struct hist_trigger_data *hist_data,
> event = data->match_data.event;
> }
>
> + if (!event)
> + goto free;
> /*
> * At this point, we're looking at a field on another
> * event. Because we can't modify a hist trigger on
> --
Tom,
Is this OK? I'm going to start running this through my tests and when
it's done, I'm going to send it off to Linus.
-- Steve
Hi Steve,
On Wed, 2021-08-11 at 10:35 -0400, Steven Rostedt wrote:
> On Sun, 8 Aug 2021 00:30:11 -0400
> Steven Rostedt <[email protected]> wrote:
>
> > diff --git a/kernel/trace/trace_events_hist.c
> > b/kernel/trace/trace_events_hist.c
> > index 949ef09dc537..a48aa2a2875b 100644
> > --- a/kernel/trace/trace_events_hist.c
> > +++ b/kernel/trace/trace_events_hist.c
> > @@ -3430,6 +3430,8 @@ trace_action_create_field_var(struct
> > hist_trigger_data *hist_data,
> > event = data->match_data.event;
> > }
> >
> > + if (!event)
> > + goto free;
> > /*
> > * At this point, we're looking at a field on another
> > * event. Because we can't modify a hist trigger on
> > --
>
> Tom,
>
> Is this OK? I'm going to start running this through my tests and when
> it's done, I'm going to send it off to Linus.
Sorry, missed this one.
But yeah, this fixes the problem, thanks!
Reviewed-by: Tom Zanussi <[email protected]>
>
> -- Steve