On 07/05/2016 04:57 PM, Jann Horn wrote:
> On Tue, Jul 05, 2016 at 05:32:30PM -0400, jeffm@xxxxxxxx wrote:
>> From: Jeff Mahoney <jeffm@xxxxxxxx>
>>
>> There are legitimate reasons to disallow mmap on certain files, notably
>> in sysfs or procfs. We shouldn't emulate mmap support on file systems
>> that don't offer support natively.
>>
>> Signed-off-by: Jeff Mahoney <jeffm@xxxxxxxx>
>> ---
>> fs/ecryptfs/file.c | 16 +++++++++++++++-
>> 1 file changed, 15 insertions(+), 1 deletion(-)
>>
>> diff --git a/fs/ecryptfs/file.c b/fs/ecryptfs/file.c
>> index 7000b96..4aaa656 100644
>> --- a/fs/ecryptfs/file.c
>> +++ b/fs/ecryptfs/file.c
>> @@ -169,6 +169,20 @@ out:
>> return rc;
>> }
>>
>> +
>> +static int ecryptfs_mmap(struct file *file, struct vm_area_struct *vma)
>> +{
>> + struct dentry *dentry = ecryptfs_dentry_to_lower(file_dentry(file));
>> + /*
>> + * Don't allow mmap on top of file systems that don't support it
>> + * natively. If FILESYSTEM_MAX_STACK_DEPTH > 2 or ecryptfs
>> + * allows recursive mounting, this will need to be extended.
>
> Or if another new stacking filesystem appears whose f_op->mmap just forwards
> to lower_f_op->mmap - but thinking about it, in that scenario, my patch
> would stop working, too.
>
> At this point, I dislike both this patch and my own one because of their
> lack of robustness. Well, at least e54ad7f1ee263ffa5a2de9c609d58dfa27b21cd9
> should be solid. :/
I agree that neither approach provides long term protection from the
attack but they fix the immediate issue at hand. Therefore, I think we
need to move forward with what we have now.
Tyler
>
>
>> + */
>> + if (!d_inode(dentry)->i_fop->mmap)
>> + return -ENODEV;
>> + return generic_file_mmap(file, vma);
>> +}
>> +
>> /**
>> * ecryptfs_open
>> * @inode: inode speciying file to open
>> @@ -403,7 +417,7 @@ const struct file_operations ecryptfs_main_fops = {
>> #ifdef CONFIG_COMPAT
>> .compat_ioctl = ecryptfs_compat_ioctl,
>> #endif
>> - .mmap = generic_file_mmap,
>> + .mmap = ecryptfs_mmap,
>> .open = ecryptfs_open,
>> .flush = ecryptfs_flush,
>> .release = ecryptfs_release,
>> --
>> 2.7.1
>>
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