lkml.org 
[lkml]   [2019]   [Jan]   [17]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: uprobes: bug in comm/string output?
From
Date
On 17.01.19 09:00, Masami Hiramatsu wrote:
> On Thu, 17 Jan 2019 15:13:09 +0900
> Masami Hiramatsu <mhiramat@kernel.org> wrote:
>
>> On Wed, 16 Jan 2019 11:16:07 +0100
>> Andreas Ziegler <andreas.ziegler@fau.de> wrote:
>>
>>>
>>> I went into this a bit deeper today, and right now it is simply failing
>>> to parse the code because there is no FETCH_OP_COMM case in
>>> process_fetch_insn() for uprobes so that will return -EILSEQ, leading to
>>> a make_data_loc(0, ...) in store_trace_args(). If we just add
>>> FETCH_OP_COMM and let val point to current->comm (that's what
>>> trace_kprobe.c does), we get an -EFAULT return value from
>>> fetch_store_string because strncpy_from_user() checks if the argument is
>>> in user space.
>>
>> Correct. I missed to add OP_COMM support. And uprobe's fetch_store_string
>> is only for user space strings.
>>
>>> So I think we might need a special case for that, something like
>>> FETCH_OP_ST_COMM_STRING which is only used for FETCH_OP_COMM and copies
>>> current->comm over to the dynamic area. The implementation could be
>>> similar to the old fetch_comm_string implementation before your rewrite.
>>
>> Hmm, instead, I would like to add current->comm checker and only allows
>> to copy that. That would be simpler and enough.
>>
>> Could you test below patch?
>>
>>
>> tracing: uprobes: Re-enable $comm support for uprobe events
>>
>> From: Masami Hiramatsu <mhiramat@kernel.org>
>>
>> Since commit 533059281ee5 ("tracing: probeevent: Introduce new
>> argument fetching code") dropped the $comm support from uprobe
>> events, this re-enable it.

this should read 're-enables'.

>>
>> For $comm support, use strncpy() instead of strncpy_from_user()
^
we're using strlcpy(), not strncpy().

>> to copy current task's comm. Because it is in the kernel space,
>> strncpy_from_user() always fails to copy the comm.
>> This also use strlen() instead of strlen_user() to measure the
^ ^
'uses', and the function should be 'strnlen_user()'.

>> length of the comm.
>>
>> Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
>> Reported-by: Andreas Ziegler <andreas.ziegler@fau.de>
>> ---
>> kernel/trace/trace_uprobe.c | 13 +++++++++++--
>> 1 file changed, 11 insertions(+), 2 deletions(-)
>>
>> diff --git a/kernel/trace/trace_uprobe.c b/kernel/trace/trace_uprobe.c
>> index e335576b9411..97d134e83e0f 100644
>> --- a/kernel/trace/trace_uprobe.c
>> +++ b/kernel/trace/trace_uprobe.c
>> @@ -156,7 +156,10 @@ fetch_store_string(unsigned long addr, void *dest, void *base)
>> if (unlikely(!maxlen))
>> return -ENOMEM;
>>
>> - ret = strncpy_from_user(dst, src, maxlen);
>> + if (addr == (unsigned long)current->comm)
>> + ret = strlcpy(dst, current->comm, maxlen);
>> + else
>> + ret = strncpy_from_user(dst, src, maxlen);
>> if (ret >= 0) {
>> if (ret == maxlen)
>> dst[ret - 1] = '\0';
>> @@ -173,7 +176,10 @@ fetch_store_strlen(unsigned long addr)
>> int len;
>> void __user *vaddr = (void __force __user *) addr;
>>
>> - len = strnlen_user(vaddr, MAX_STRING_SIZE);
>> + if (addr == (unsigned long)current->comm)
>> + len = strlen(current->comm);
>
> To balance with the strnlen_user, we must increse the len in this block.
> (strlen doesn't count the final '\0', but strnlen_user counts it)
>

yes, we need to add a '+ 1' here.

With the typos and this one fixed, this is

Acked-by: Andreas Ziegler <andreas.ziegler@fau.de>

> Thank you,
>
>> + else
>> + len = strnlen_user(vaddr, MAX_STRING_SIZE);
>>
>> return (len > MAX_STRING_SIZE) ? 0 : len;
>> }
>> @@ -213,6 +219,9 @@ process_fetch_insn(struct fetch_insn *code, struct pt_regs *regs, void *dest,
>> case FETCH_OP_IMM:
>> val = code->immediate;
>> break;
>> + case FETCH_OP_COMM:
>> + val = (unsigned long)current->comm;
>> + break;
>> case FETCH_OP_FOFFS:
>> val = translate_user_vaddr(code->immediate);
>> break;
>
>

\
 
 \ /
  Last update: 2019-01-17 09:09    [W:0.079 / U:3.372 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site