2022-11-16 02:11:06

by Xiu Jianfeng

Subject: [PATCH] ftrace: Fix null pointer dereference in ftrace_add_mod()

The @ftrace_mod is allocated by kzalloc(), so both the members {prev,next}
of @ftrace_mode->list are NULL, it's not a valid state to call list_del().
If kstrdup() for @ftrace_mod->{func|module} fails, it goes to @out_free
tag and calls free_ftrace_mod() to destroy @ftrace_mod, then list_del()
will write prev->next and next->prev, where null pointer dereference
happens.

BUG: kernel NULL pointer dereference, address: 0000000000000008
Oops: 0002 [#1] PREEMPT SMP NOPTI
Call Trace:
<TASK>
ftrace_mod_callback+0x20d/0x220
? do_filp_open+0xd9/0x140
ftrace_process_regex.isra.51+0xbf/0x130
ftrace_regex_write.isra.52.part.53+0x6e/0x90
vfs_write+0xee/0x3a0
? __audit_filter_op+0xb1/0x100
? auditd_test_task+0x38/0x50
ksys_write+0xa5/0xe0
do_syscall_64+0x3a/0x90
entry_SYSCALL_64_after_hwframe+0x63/0xcd
Kernel panic - not syncing: Fatal exception

So call INIT_LIST_HEAD() to initialize the list member to fix this issue.

Fixes: 673feb9d76ab ("ftrace: Add :mod: caching infrastructure to trace_array")
Signed-off-by: Xiu Jianfeng <[email protected]>
---
kernel/trace/ftrace.c | 1 +
1 file changed, 1 insertion(+)

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 705b990d264d..9af0c4065b4e 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -1289,6 +1289,7 @@ static int ftrace_add_mod(struct trace_array *tr,
if (!ftrace_mod)
return -ENOMEM;

+ INIT_LIST_HEAD(&ftrace_mod->list);
ftrace_mod->func = kstrdup(func, GFP_KERNEL);
ftrace_mod->module = kstrdup(module, GFP_KERNEL);
ftrace_mod->enable = enable;
--
2.17.1

2022-11-17 22:37:33

by Steven Rostedt

Subject: Re: [PATCH] ftrace: Fix null pointer dereference in ftrace_add_mod()

On Wed, 16 Nov 2022 09:52:07 +0800
Xiu Jianfeng <[email protected]> wrote:

> The @ftrace_mod is allocated by kzalloc(), so both the members {prev,next}
> of @ftrace_mode->list are NULL, it's not a valid state to call list_del().
> If kstrdup() for @ftrace_mod->{func|module} fails, it goes to @out_free
> tag and calls free_ftrace_mod() to destroy @ftrace_mod, then list_del()
> will write prev->next and next->prev, where null pointer dereference
> happens.
>
> BUG: kernel NULL pointer dereference, address: 0000000000000008
> Oops: 0002 [#1] PREEMPT SMP NOPTI
> Call Trace:
> <TASK>
> ftrace_mod_callback+0x20d/0x220
> ? do_filp_open+0xd9/0x140
> ftrace_process_regex.isra.51+0xbf/0x130
> ftrace_regex_write.isra.52.part.53+0x6e/0x90
> vfs_write+0xee/0x3a0
> ? __audit_filter_op+0xb1/0x100
> ? auditd_test_task+0x38/0x50
> ksys_write+0xa5/0xe0
> do_syscall_64+0x3a/0x90
> entry_SYSCALL_64_after_hwframe+0x63/0xcd
> Kernel panic - not syncing: Fatal exception
>
> So call INIT_LIST_HEAD() to initialize the list member to fix this issue.
>
> Fixes: 673feb9d76ab ("ftrace: Add :mod: caching infrastructure to trace_array")
> Signed-off-by: Xiu Jianfeng <[email protected]>
> ---


Queued. Thanks Xiu!

-- Steve