lists.openwall.net   lists  /  announce  owl-users  owl-dev  john-users  john-dev  passwdqc-users  yescrypt  popa3d-users  /  oss-security  kernel-hardening  musl  sabotage  tlsify  passwords  /  crypt-dev  xvendor  /  Bugtraq  Full-Disclosure  linux-kernel  linux-netdev  linux-ext4  linux-hardening  linux-cve-announce  PHC 
Open Source and information security mailing list archives
 
Hash Suite: Windows password security audit tool. GUI, reports in PDF.
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Date:	Fri, 13 Apr 2012 10:10:22 +1000
From:	Dave Chinner <david@...morbit.com>
To:	Jouni Siren <jouni.siren@....fi>
Cc:	linux-ext4@...r.kernel.org
Subject: Re: Bug: Large writes can fail on ext4 if the write buffer is not
 empty

On Thu, Apr 12, 2012 at 05:47:41PM +0300, Jouni Siren wrote:
> Hi,
> 
> I recently ran into problems when writing large blocks of data (more than about 2 GB) with a single call, if there is already some data in the write buffer. The problem seems to be specific to ext4, or at least it does not happen when writing to nfs on the same system. Also, the problem does not happen, if the write buffer is flushed before the large write.
> 
> The following C++ program should write a total of 4294967304 bytes, but I end up with a file of size 2147483664.
> 
> #include <fstream>
> 
> int
> main(int argc, char** argv)
> {
>   std::streamsize data_size = (std::streamsize)1 << 31;
>   char* data = new char[data_size];
> 
>   std::ofstream output("test.dat", std::ios_base::binary);
>   output.write(data, 8);
>   output.write(data, data_size);
>   output.write(data, data_size);
>   output.close();
> 
>   delete[] data;
>   return 0;
> }
> 
> 
> The relevant part of strace is the following:
> 
> open("test.dat", O_WRONLY|O_CREAT|O_TRUNC, 0666) = 3
> writev(3, [{"\0\0\0\0\0\0\0\0", 8}, {"", 2147483648}], 2) = -2147483640
> writev(3, [{0xffffffff80c6d258, 2147483648}, {"", 2147483648}], 2) = -1 EFAULT (Bad address)

EFAULT - your user buffer is too large.

IOWs, you can't do IO in chunks of 2GB or greater in a single buffer
or iovec. This limit is imposed by the VFS to prevent overflows in
badly implemented filesystem code.

Just do mulitple smaller IOs - it will be just as to do a single 2GB
IO....

Cheers,

Dave.

-- 
Dave Chinner
david@...morbit.com
--
To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html

Powered by blists - more mailing lists