Dict proxy client returning empty string instead of multiline string

[Aki Tuomi]

Hi!

This does sound like a bug, we'll have look.

Aki


On 17.10.2016 01:26, Pierre Jaury wrote:
> I dived a little bit further into the rabbit hole, up to the point where
> debugging has become unpracticle but I still haven't found the root
> cause for sure.
>
> I read most of the code for "p_strdup" based on datastack memory pools
> (which are used for dictionary lookups both with doveadm and by extdata)
> and it seems ok. Still, after "t_malloc_real" is called in "t_malloc0",
> the allocated buffer has the same address as the source string.
>
> The only sensible explanation I can come up with is that during
> unescaping, strings are not allocated properly, leading to the memory
> pool reusing the string address and zeroing it in the process before the
> string copy operation.
>
> I will follow on this path tomorrow, any lead is more than welcome.
>
> kaiyou.
>
> On 10/16/2016 11:16 PM, Pierre Jaury wrote:
>> Hello,
>>
>> I am using a dict proxy for my sieve extdata plugin to access some
>> fields from an SQLite database (autoreply text and other
>> database-configured items).
>>
>> All tests are performed against version 2.2.25.
>>
>>   $ dovecot --version
>>   2.2.25 (7be1766)
>>
>> My configuration looks like:
>>
>>   dict {
>>     sieve = sqlite:/etc/dovecot/pigeonhole-sieve.dict
>>   }
>>
>>   [...]
>>   sieve_extdata_dict_uri = proxy::sieve
>>
>> I am able to read pretty much any attribute without any issue, except
>> when the value contains a special character like "\r" or "\n". By using
>> the doveadm dict client, I narrowed it down to the dictionary management
>> part (either server, protocol or client).
>>
>> I was suspecting escaping functions from "lib/strescape.c" (mostly
>> str_tabescape and its counterpart, used by "lib-dict/client.c"), so I
>> monitored socket communications. It seems that escaping is done properly
>> on the server and the socket is not an issue either.
>>
>> The following strace dump results from running "doveadm dict get"
>> against the dict socket:
>>
>>   connect(8, {sa_family=AF_UNIX, sun_path="..."}, 110) = 0
>>   fstat(8, {st_mode=S_IFSOCK|0777, st_size=0, ...}) = 0
>>   [...]
>>   write(8, "H2\t0\t0\tadmin at domain.tld\tsieve\n", 30) = 30
>>   [...]
>>   read(8, "Otest\1r\1ntest\n", 8192)      = 14
>>
>> Indeed "\1r" and "\1n" are the escape sequences used by
>> "lib/strescape.c". I went deeped and debugged the call to "dict_lookup"
>> performed by doveadm. Indeed the client gets the proper string from the
>> socket and to my surprise, it is properly unescaped.
>>
>> Then, in "client_dict_lookup" ("lib-dict/dict-client.c"), the call to
>> "p_strdup" returns an empty string (null byte set at the target address).
>>
>> Before the call to the dict "->lookup" attribute (client_dict_lookup):
>>
>>    RAX: 0x7ffff73a37c0 (push   r14)
>>    RBX: 0x6831b8 ("priv/reply_body")
>>    RCX: 0x7fffffffe240 --> 0x682a60 --> 0x6831b8 ("priv/reply_body")
>>    RDX: 0x6831b8 ("priv/reply_body")
>>    RSI: 0x683288 --> 0x7ffff7653120 --> 0x7ffff73ea620 ([...])
>>    RDI: 0x690ad0 --> 0x7ffff7400713 --> 0x75250079786f7270 ('proxy')
>>
>>    0x7ffff73a1f10 <dict_lookup+32>:	mov    rcx,r11 (value_r)
>>    0x7ffff73a1f13 <dict_lookup+35>:	mov    rdx,r8 (key)
>>    0x7ffff73a1f16 <dict_lookup+38>:	mov    rsi,r10 (pool)
>>    0x7ffff73a1f19 <dict_lookup+41>:	mov    rdi,r9 (dict)
>>    0x7ffff73a1f1c <dict_lookup+44>:	add    rsp,0x8
>> => 0x7ffff73a1f20 <dict_lookup+48>:	jmp    rax
>>
>> Before the call to p_strdup in "client_dict_lookup":
>>
>>    RSI: 0x6832d8 ("test\r\ntest") (lookup.result.value)
>>    RDI: 0x683288 --> 0x7ffff7653120 --> [...] (pool)
>>    RAX: 0x0 (result)
>>
>>    0x7ffff73a384f:	nop
>>    0x7ffff73a3850:	mov    rsi,QWORD PTR [rsp+0x8]
>>    0x7ffff73a3855:	mov    rdi,r14
>> => 0x7ffff73a3858:	call   0x7ffff736d3c0 <p_strdup at plt>
>>    0x7ffff73a385d:	mov    QWORD PTR [r13+0x0],rax
>>    0x7ffff73a3861:	mov    rsi,QWORD PTR [rsp+0x18]
>>    0x7ffff73a3866:	xor    rsi,QWORD PTR fs:0x28
>>    0x7ffff73a386f:	mov    eax,ebx
>>
>> After the call:
>>
>>    0x7ffff73a3850:	mov    rsi,QWORD PTR [rsp+0x8]
>>    0x7ffff73a3855:	mov    rdi,r14
>>    0x7ffff73a3858:	call   0x7ffff736d3c0 <p_strdup at plt>
>> => 0x7ffff73a385d:	mov    QWORD PTR [r13+0x0],rax
>>    0x7ffff73a3861:	mov    rsi,QWORD PTR [rsp+0x18]
>>    0x7ffff73a3866:	xor    rsi,QWORD PTR fs:0x28
>>    0x7ffff73a386f:	mov    eax,ebx
>>    0x7ffff73a3871:	jne    0x7ffff73a38da
>>
>>    RSI: 0x0
>>    RDI: 0x6832d8 --> 0x0
>>    RAX: 0x6832d8 --> 0x0 (result)
>>
>> It is worth noting that I can reproduce the exact same execution flow
>> with a non-multiline result string (lookup.result.value) that is
>> properly copied by "p_strdup" and returned in RAX, then displayed by
>> doveadm.
>>
>> I am not familiar with the pooling mechanism hidden behind the call to
>> p_strdump and not quite sure why this behaviour is emerging. Maybe I am
>> even miles away from an understanding of the issue here, but it sounds
>> to me like something is wrong in the way "p_strdup" performs the copy.
>>
>> Hope this helps,
>> kaiyou.
>>
>>
>>