Bugs item #3004787, was opened at 2010-05-20 16:07
Message generated for change (Tracker Item Submitted) made by kilpatds
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Category: TFTP
Group: wrong behaviour
Status: Open
Resolution: None
Priority: 5
Private: No
Submitted By: Douglas Kilpatrick (kilpatds)
Assigned to: Daniel Stenberg (bagder)
Summary: Curl's tftp does not properly handle block number wrap.

Initial Comment:
In the tftp protocol, the block count is a 16-bit unsigned variable, that starts at 1 Obviously, this will wrap after around 65k blocks. In a non-multicast situation, that's usually not a problem as the protocol only allows one outstanding packet at any given point in time. So ... block# 65535 is followed by block# 0.

However, curl doesn't seem to support this correctly. The tftp binary is the simple (doesn't support options) system binary, also using a 512 block size.

$ ls -l /tftpboot/foo4
-rw-r--r-- 1 root root 33554944 May 17 14:53 /tftpboot/foo4
$ rm -f foo4 && tftp localhost -c get foo4 && ls -l foo4
-rw-rw-r-- 1 dkilpatr dkilpatr 33554944 May 20 11:59 foo4
$ rm -f foo4 && ~/bin/curl -s -o foo4 tftp://localhost/foo4 && ls -l foo4
-rw-rw-r-- 1 dkilpatr dkilpatr 33554432 May 20 11:59 foo4
$ ~/bin/curl -V
curl 7.20.1 (x86_64-unknown-linux-gnu) libcurl/7.20.1 OpenSSL/0.9.8b zlib/1.2.3 libidn/0.6.5
Protocols: dict file ftp ftps http https imap imaps ldap pop3 pop3s rtsp smtp smtps telnet tftp
Features: IDN IPv6 Largefile NTLM SSL libz
$ echo $(( 33554944 / 512 ))
65537
$ echo $(( 33554432 / 512 ))
65536

That 65536 blocks were saved is somewhat surprising... the block number starts at 1, and so only 65535 blocks are transfered before the blocknumber wraps.

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Received on 2010-05-20