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:	Sun, 11 Nov 2012 18:54:27 -0700
From:	Andreas Dilger <>
To:	"George Spelvin" <>
Subject: Re: mke2fs -O 64bit -E resize=<anything> divides by 0

On 2012-11-11, at 3:27 PM, George Spelvin wrote:
> I'm using v1.43-WIP-2012-09-22-10-g41bf599, last commit Oct. 14.
> I'm trying to create a file system with 64bit support and specify a
> maximum resize limit of 64 TiB = 2^34 blocks = 17179869184.
> (gdb) run -n -t ext4 -O 64bit -E resize=4294967296 /dev/md1
> Starting program: /root/e2fsprogs/misc/mke2fs -n -t ext4 -O 64bit -E resize=4294967295 /dev/md1
> [Thread debugging using libthread_db enabled]
> Using host libthread_db library "/lib/x86_64-linux-gnu/".
> mke2fs 1.43-WIP (22-Sep-2012)
> Program received signal SIGFPE, Arithmetic exception.
> 0x0000000000405f5a in parse_extended_opts (opts=<optimized out>, 
>   param=0x64e200) at mke2fs.c:800
> 800                             gdpb = EXT2_DESC_PER_BLOCK(param);

This is definitely a bug in the code to do a divide-by-zero.

However, it should be pointed out that the "resize" option does not
make sense for filesystems larger than 16TB.  The mechanism used for
resizing beyond 16TB is different and does not need to reserve blocks.

Cheers, Andreas.

> The issue is that 
> #define EXT2_DESC_PER_BLOCK(s)          (EXT2_BLOCK_SIZE(s) / EXT2_DESC_SIZE(s))
> #define EXT2_DESC_SIZE(s)                                                \
>      ((EXT2_SB(s)->s_feature_incompat & EXT4_FEATURE_INCOMPAT_64BIT) ? \
>       (s)->s_desc_size : EXT2_MIN_DESC_SIZE)
> and s_desc_size is 0 because parse_extended_opts is called from PRS which
> is called very early in main() at line 2320, while s_desc_size is set up
> in ext2fs_initialize, which is not called from main() until mke2fs.c:2353.
> As a temporary workaround, I notice that ext2fs_initialize sets s_desc_size to
> the fixed value EXT2_MIN_DESC_SIZE_64BIT, so I changed the #define as follows:
> #define EXT2_DESC_SIZE(s)                                                \
>      ((EXT2_SB(s)->s_feature_incompat & EXT4_FEATURE_INCOMPAT_64BIT) ? \
>       (s)->s_desc_size ?: EXT2_MIN_DESC_SIZE_64BIT : EXT2_MIN_DESC_SIZE)
> ... which seems to work.
> (One point that occurred to me while wrestling with this is that the
> default resize limit of initial size * 1000 should perhaps be clamped
> to 2^32 if 64bit is not enabled.)
> --
> To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
> the body of a message to
> More majordomo info at

Cheers, Andreas

To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
the body of a message to
More majordomo info at

Powered by blists - more mailing lists