Re: [PATCH] btrfs: prevent heap corruption in btrfs_ioctl_space_info()

[Josef Bacik <josef@redhat.com>]

On Wed, Feb 09, 2011 at 09:12:46AM -0500, Dan Rosenberg wrote:
> Commit bf5fc093c5b625e4259203f1cee7ca73488a5620 refactored
> btrfs_ioctl_space_info() and introduced several security issues.
> 
> space_args.space_slots is an unsigned 64-bit type controlled by a
> possibly unprivileged caller.  The comparison as a signed int type
> allows providing values that are treated as negative and cause the
> subsequent allocation size calculation to wrap, or be truncated to 0.
> By providing a size that's truncated to 0, kmalloc() will return
> ZERO_SIZE_PTR.  It's also possible to provide a value smaller than the
> slot count.  The subsequent loop ignores the allocation size when
> copying data in, resulting in a heap overflow or write to ZERO_SIZE_PTR.
> 
> The fix changes the slot count type and comparison typecast to u64,
> which prevents truncation or signedness errors, and also ensures that we
> don't copy more data than we've allocated in the subsequent loop.  Note
> that zero-size allocations are no longer possible since there is already
> an explicit check for space_args.space_slots being 0 and truncation of
> this value is no longer an issue.
> 
> Signed-off-by: Dan Rosenberg <drosenberg@vsecurity.com>

Reviewed-by: Josef Bacik <josef@redhat.com>

Thanks,

Josef