Re: [Dovecot] attachment sis + EMLINK (too many links) = segfault bug (2.2.12)

[Pavel Stano]

Hi,

attached patch fix problem with segfault when EMLINK happend when file
has too many hard link.



On Fri, 30 May 2014 17:02:47 +0200 Pavel Stano <st...@websupport.sk>
wrote:

> Hi,
> 
> we use attachment dedup with lots of emails (still migrating to it
> from maildir).
> We use netapp storage with wafl filesystem over nfs.
> Problem is that netapp has hard limit of 100k hardlinks to one file.
> And we encountered it.
> 
> Problem is that dovecot start do segfault (lmtp,dsync,pop3 etc) when
> it happend when tried to deliver new emails with that attachment.
> Here is strace of dsync:
> 
> 6740
> link("/nfsmnt/mailatch1/f9/10/hashes/f9108ddaa156ac15738e41ed3bedec1eda50175d",
> "/nfsmnt/mailatch1/f9/10/f9108ddaa156ac15738e41ed3bedec1eda50175d-7bb7a20ddb598853541a000028db4a9f")
> = -1 EMLINK (Too many links) 6740  --- SIGSEGV (Segmentation fault) @
> 0 (0) ---
> 
> ls -lh:
> -rw------- 100000 vmail vmail 4.7K Apr 28
> 16:54 /nfsmnt/mailatch1/f9/10/hashes/f9108ddaa156ac15738e41ed3bedec1eda50175d
> 
> We were using mail_attachment_min_size=4kb, we solve it by increasing
> it to 8kb.
> 
> It would be nice to somehow fix this problem. Like not crash when
> EMLINK happend and maybe do not deduplicate attachments but deliver
> email without dedup.
> Or create second file in hashes/ and start hardlinking it instead of
> original.
> 
> AFAIK ext4 has also hard-link limit 64k
> (http://en.wikipedia.org/wiki/Hard_link#Limitations_of_hard_links)
> So this can happen to anyone with lots of emails.
> 
> Thanks



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Pavel Stano | Troubleshooter

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diff -ru dovecot-2.2.13/src/lib-fs/fs-sis.c dovecot-2.2.13.fixed/src/lib-fs/fs-sis.c
--- dovecot-2.2.13/src/lib-fs/fs-sis.c	2014-02-04 22:28:38.000000000 +0100
+++ dovecot-2.2.13.fixed/src/lib-fs/fs-sis.c	2014-06-05 16:05:30.768976354 +0200
@@ -395,7 +395,9 @@
 			return 1;
 		}
 	}
-	o_stream_unref(&_file->output);
+    if (_file->output != NULL) {
+    	o_stream_unref(&_file->output);
+    }
 
 	if (fs_write_stream_finish(file->super, &file->fs_output) < 0) {
 		fs_sis_file_copy_error(file);

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