Re: [PATCH][v2] proc: use vmalloc for our kernel buffer

Josef Bacik
2020-08-13T15:40:08Z

On 8/13/20 11:37 AM, Christoph Hellwig wrote:
> On Thu, Aug 13, 2020 at 11:33:56AM -0400, Josef Bacik wrote:
>> Since
>>
>> sysctl: pass kernel pointers to ->proc_handler
>>
>> we have been pre-allocating a buffer to copy the data from the proc
>> handlers into, and then copying that to userspace. The problem is this
>> just blind kmalloc()'s the buffer size passed in from the read, which in
>> the case of our 'cat' binary was 64kib. Order-4 allocations are not
>> awesome, and since we can potentially allocate up to our maximum order,
>> use vmalloc for these buffers.
>>
>> Fixes: 32927393dc1c ("sysctl: pass kernel pointers to ->proc_handler")
>> Signed-off-by: Josef Bacik <josef@toxicpanda.com>
>> ---
>> v1->v2:
>> - Make vmemdup_user_nul actually do the right thing...sorry about that.
>>
>> fs/proc/proc_sysctl.c | 6 +++---
>> include/linux/string.h | 1 +
>> mm/util.c | 27 +++++++++++++++++++++++++++
>> 3 files changed, 31 insertions(+), 3 deletions(-)
>>
>> diff --git a/fs/proc/proc_sysctl.c b/fs/proc/proc_sysctl.c
>> index 6c1166ccdaea..207ac6e6e028 100644
>> --- a/fs/proc/proc_sysctl.c
>> +++ b/fs/proc/proc_sysctl.c
>> @@ -571,13 +571,13 @@ static ssize_t proc_sys_call_handler(struct file *filp, void __user *ubuf,
>> goto out;
>>
>> if (write) {
>> - kbuf = memdup_user_nul(ubuf, count);
>> + kbuf = vmemdup_user_nul(ubuf, count);
>
> Given that this can also do a kmalloc and thus needs to be paired
> with kvfree shouldn't it be kvmemdup_user_nul?
>

There's an existing vmemdup_user that does kvmalloc, so I followed the existing
naming convention. Do you want me to change them both? Thanks,

Josef