Dict proxy client returning empty string instead of multiline string

[Pierre Jaury]

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.