On Thursday 22 of March 2018, Arkadiusz Miśkiewicz wrote:
I have a problem with some messages passed from exim to dovecot lmtp service:
From exim debug:
using socket /var/run/dovecot/lmtp LMTP<< 220 mbox8 ready LMTP>> LHLO mbox8... LMTP<< 250-mbox8 LMTP<< 250-STARTTLS LMTP<< 250-8BITMIME LMTP<< 250-ENHANCEDSTATUSCODES LMTP<< 250 PIPELINING LMTP>> MAIL FROM:... LMTP<< 250 2.1.0 OK LMTP>> RCPT TO:... LMTP<< 250 2.1.5 OK LMTP>> DATA LMTP<< 354 OK LMTP>> writing message and terminating "." cannot use sendfile for body: terminating dot wanted writing data block fd=6 size=6585 timeout=300 LMTP>> QUIT LMTP<< 421 4.4.2 mbox8 Disconnected client for inactivity
now above "writting message and terminating" according to exim strace looks like this:
13413 22:07:24 write(2, " LMTP>> writing message and terminating \".\"\n", 45) = 45 <0.000018> 13413 22:07:24 stat("/etc/localtime", {st_mode=S_IFREG|0644, st_size=2705, ...}) = 0 <0.000025> 13413 22:07:24 write(2, "cannot use sendfile for body: terminating dot wanted\n", 53) = 53 <0.000022> 13413 22:07:24 lseek(3, 19, SEEK_SET) = 19 <0.000015> [...] 13413 22:07:24 write(2, "writing data block fd=6 size=6585 timeout=300\n", 46) = 46 <0.000019> 13413 22:07:24 alarm(300) = 0 <0.000013> 13413 22:07:24 write(6, "Return-path: [...] \nwrap\"><br></span></div>.\n", 6585) = 6585 <0.000023>
and then exim waits for dovecot lmtp to say it accepted message but lmtp never does that.
Isn't .\n always enough for dovecot to signal end of message? Because exim wrote full message to dovecot lmtp unix socket.
Now the interesting this - exim does only one write() with 6585 bytes to write that message to lmtp. If exim needs more than one write() to do that (message is larger by some buffer) then it succeeds, dovecot accepts it.
Could dovecot lmtp handling for single write() case be broken?
dovecot 2.2.35
And reproducer. Both messages have ".\n" as ending but one has \r\n before it.
#!/usr/bin/python3
import socket
c = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM) c.connect("/var/run/dovecot/lmtp") print(c.recv(1024)) print("LHLO") c.send(b"LHLO mbox8\r\n") print(c.recv(1024)) print("MAIL FROM") c.send(b"MAIL FROM:someone@example.com\r\n") print(c.recv(1024)) print("RCPT TO") c.send(b"RCPT TO:arekm@example.com\r\n") print(c.recv(1024)) print("DATA") c.send(b"DATA\r\n") print(c.recv(1024)) print("body...")
msg_fail = b"testtest<br></span></div>.\n" msg_ok = b"01, 41.82, 30.14\r\n.\n"
#c.send(msg_ok)
c.send(msg_fail)
print(c.recv(1024))
c.close()
-- Arkadiusz Miśkiewicz, arekm / ( maven.pl | pld-linux.org )