[Opendnssec-user] svn r6114

[Matthijs Mekking]

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Using mkstemp will not solve this attack, since you can do the same
trick for /the/zone-name (without .tmp), or any other file location
OpenDNSSEC is using.

Best regards,
  Matthijs

On 02/02/2012 01:22 PM, Bernhard Reutner-Fischer wrote:
> On 2 February 2012 10:25, Matthijs Mekking <matthijs at nlnetlabs.nl>
> wrote:
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>> 
>> Hi Bernhard,
>> 
>> mkstemp returns a file descriptor (int), while for printing the
>> zone, I expect a stream (FILE*). What symlink problems do you
>> expect?
> 
> It seems that the signer will usually not run with higher
> privileges, but still, avoiding potential symlink attacks is always
> a good thing. The zonefile-name is known, let's say i make a
> symlink called /the/zone-name.tmp to /etc/nologin (won't do much
> harm unless the signer runs as root but will prevent the signer to
> work), /dev/log, some socket that is under my control, etc. You get
> the idea.
> 
> As to the FILE*:
> 
> #include <stdlib.h> #include <stdio.h> #include <errno.h> #include
> <string.h> #include <unistd.h> #include <sys/stat.h> int main(void)
> { char template[] =
> "/var/tmp/or_var_lib_ods_tmp.DELME.12321.XXXXXX"; int fd =
> mkstemp(template); /* for some very good reason(?) i absolutely
> must use buffered I/O ..*/ FILE *file = fdopen(fd, "w"); if (file
> == NULL) { printf("ERROR: %s", strerror(errno)); 
> exit(EXIT_FAILURE); } fprintf(file, "something\n"); fclose(file); 
> chmod(template, 0640); rename(template, "/tmp/done"); 
> exit(EXIT_SUCCESS); }
> 
>> 
>> I agree that logging problems with rename() would be useful, I
>> will apply your patch.
> 
> Great, thanks!

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