Hi Masami,
yes, that patch looks like a good compromise between the
original code and the new patch. To reduce the number of if
statements involving ret we would need to move more things
around and I think it's best to avoid that (as you also said).
I'd say you can update this for the other kernel stable trees
as well.
Thank you!
Andreas
P.S.: Do we need to explain in the commit message why
backporting is needed?
> On 14. Feb 2019, at 15:30, Masami Hiramatsu <mhiramat@xxxxxxxxxx> wrote:
>
> Hi Andreas,
>
> I've update this patch to include "ret == maxlen" case fix
> as similar to the latest kernel code.
>
> Please review it. If it is OK, I'll update patches for other
> stable trees.
>
> Thank you,
>
> On Thu, 14 Feb 2019 23:24:29 +0900
> Masami Hiramatsu <mhiramat@xxxxxxxxxx> wrote:
>
>> From: Andreas Ziegler <andreas.ziegler@xxxxxx>
>>
>> commit 0722069a5374b904ec1a67f91249f90e1cfae259 upstream.
>>
>> When printing multiple uprobe arguments as strings the output for the
>> earlier arguments would also include all later string arguments.
>>
>> This is best explained in an example:
>>
>> Consider adding a uprobe to a function receiving two strings as
>> parameters which is at offset 0xa0 in strlib.so and we want to print
>> both parameters when the uprobe is hit (on x86_64):
>>
>> $ echo 'p:func /lib/strlib.so:0xa0 +0(%di):string +0(%si):string' > \
>> /sys/kernel/debug/tracing/uprobe_events
>>
>> When the function is called as func("foo", "bar") and we hit the probe,
>> the trace file shows a line like the following:
>>
>> [...] func: (0x7f7e683706a0) arg1="foobar" arg2="bar"
>>
>> Note the extra "bar" printed as part of arg1. This behaviour stacks up
>> for additional string arguments.
>>
>> The strings are stored in a dynamically growing part of the uprobe
>> buffer by fetch_store_string() after copying them from userspace via
>> strncpy_from_user(). The return value of strncpy_from_user() is then
>> directly used as the required size for the string. However, this does
>> not take the terminating null byte into account as the documentation
>> for strncpy_from_user() cleary states that it "[...] returns the
>> length of the string (not including the trailing NUL)" even though the
>> null byte will be copied to the destination.
>>
>> Therefore, subsequent calls to fetch_store_string() will overwrite
>> the terminating null byte of the most recently fetched string with
>> the first character of the current string, leading to the
>> "accumulation" of strings in earlier arguments in the output.
>>
>> Fix this by incrementing the return value of strncpy_from_user() by
>> one if we did not hit the maximum buffer size.
>>
>> Link: http://lkml.kernel.org/r/20190116141629.5752-1-andreas.ziegler@xxxxxx
>>
>> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
>> Cc: stable@xxxxxxxxxxxxxxx
>> Fixes: 5baaa59ef09e ("tracing/probes: Implement 'memory' fetch method for uprobes")
>> Acked-by: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
>> Signed-off-by: Andreas Ziegler <andreas.ziegler@xxxxxx>
>> Signed-off-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>
>> Signed-off-by: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
>> ---
>> kernel/trace/trace_uprobe.c | 9 ++++++++-
>> 1 file changed, 8 insertions(+), 1 deletion(-)
>>
>> diff --git a/kernel/trace/trace_uprobe.c b/kernel/trace/trace_uprobe.c
>> index e696667da29a..bf93ae152c22 100644
>> --- a/kernel/trace/trace_uprobe.c
>> +++ b/kernel/trace/trace_uprobe.c
>> @@ -141,7 +141,14 @@ static void FETCH_FUNC_NAME(memory, string)(struct pt_regs *regs,
>>
>> ret = strncpy_from_user(dst, src, maxlen);
>> if (ret == maxlen)
>> - dst[--ret] = '\0';
>> + dst[ret - 1] = '\0';
>> + else if (ret >= 0)
>> + /*
>> + * Include the terminating null byte. In this case it
>> + * was copied by strncpy_from_user but not accounted
>> + * for in ret.
>> + */
>> + ret++;
>>
>> if (ret < 0) { /* Failed to fetch string */
>> ((u8 *)get_rloc_data(dest))[0] = '\0';
>>
>
>
> --
> Masami Hiramatsu <mhiramat@xxxxxxxxxx>
