On Sep 04, 2009 22:21 -0500, Eric Sandeen wrote:
> Today, the ext4 allocator will happily allocate blocks past
> 232 for indirect-block files, which results in the block
> numbers getting truncated, and corruption ensues.
>
> This patch limits such allocations to < 2^32, and adds
> WARN_ONs (maybe should be BUG_ONs) if we do get blocks
> larger than that.
Eric, thanks for making the patch.
> This should address RH Bug 519471, ext4 bitmap allocator must limit
> blocks to < 2^32
>
> * ext4_find_goal() is modified to choose a goal < UINT_MAX,
> so that our starting point is in an acceptable range.
>
> * ext4_xattr_block_set() is modified such that the goal block
> is < UINT_MAX, as above.
Using UINT_MAX probably isn't wholly safe, as I know of systems
that have e.g. 64-bit ints (though I guess none that have Linux
kernel ports). It should use (u32)~0 or ((1 << 32) - 1) directly.
> Perhaps an ext4-specific #define would be better than UINT_MAX?
I think yes, since we know the maximum value is tied specifically
to the u32 indirect block pointers, and not necessarily to an "int".
> static ext4_fsblk_t ext4_find_goal(struct inode *inode, ext4_lblk_t block,
> Indirect *partial)
> {
> + goal = ext4_find_near(inode, partial);
> + goal = goal % UINT_MAX;
> + return goal;
Using "% UINT_MAX" here will result in a 64-bit division on 32-bit
platforms, since ext4_fsblk_t is declared as an unsigned long long.
This should instead be "(u32)" or "& 0xffffffff".
> @@ -1943,6 +1943,11 @@ ext4_mb_regular_allocator(struct ext4_allocation_context *ac)
> + /* non-extent files are limited to low blocks/groups */
> + if (!(EXT4_I(ac->ac_inode)->i_flags & EXT4_EXTENTS_FL))
> + ngroups = min_t(unsigned long, ngroups,
> + (UINT_MAX / EXT4_BLOCKS_PER_GROUP(sb)));
Since EXT4_BLOCKS_PER_GROUP() is a run-time variable, but is constant
for the life of the filesystem, this could be computed once and stored
in the superblock?
> +++ b/fs/ext4/xattr.c
> @@ -810,12 +810,22 @@ inserted:
> + if (!(EXT4_I(inode)->i_flags & EXT4_EXTENTS_FL))
> + goal = goal % UINT_MAX;
As above.
Cheers, Andreas
--
Andreas Dilger
Sr. Staff Engineer, Lustre Group
Sun Microsystems of Canada, Inc.
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