Re: [PATCH] RDMA/ucma: Put a lock around every call to the rdma_cm layer

[Jason Gunthorpe <jgg@ziepe.ca>]

On Tue, Feb 18, 2020 at 09:04:36PM +0000, Jason Gunthorpe wrote:
> The rdma_cm must be used single threaded.
> 
> This appears to be a bug in the design, as it does have lots of locking
> that seems like it should allow concurrency. However, when it is all said
> and done every single place that uses the cma_exch() scheme is broken, and
> all the unlocked reads from the ucma of the cm_id data are wrong too.
> 
> syzkaller has been finding endless bugs related to this.
> 
> Fixing this in any elegant way is some enormous amount of work. Take a
> very big hammer and put a mutex around everything to do with the
> ucma_context at the top of every syscall.
> 
> Fixes: 75216638572f ("RDMA/cma: Export rdma cm interface to userspace")
> Reported-by: syzbot+adb15cf8c2798e4e0db4@syzkaller.appspotmail.com
> Reported-by: syzbot+e5579222b6a3edd96522@syzkaller.appspotmail.com
> Reported-by: syzbot+4b628fcc748474003457@syzkaller.appspotmail.com
> Reported-by: syzbot+29ee8f76017ce6cf03da@syzkaller.appspotmail.com
> Reported-by: syzbot+6956235342b7317ec564@syzkaller.appspotmail.com
> Reported-by: syzbot+b358909d8d01556b790b@syzkaller.appspotmail.com
> Reported-by: syzbot+6b46b135602a3f3ac99e@syzkaller.appspotmail.com
> Reported-by: syzbot+8458d13b13562abf6b77@syzkaller.appspotmail.com
> Reported-by: syzbot+bd034f3fdc0402e942ed@syzkaller.appspotmail.com
> Reported-by: syzbot+c92378b32760a4eef756@syzkaller.appspotmail.com
> Reported-by: syzbot+68b44a1597636e0b342c@syzkaller.appspotmail.com
> Cc: Eric Biggers <ebiggers@kernel.org>
> Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>
> ---
>  drivers/infiniband/core/ucma.c | 50 ++++++++++++++++++++++++++++++++--
>  1 file changed, 48 insertions(+), 2 deletions(-)

It has had some testing on the Mellanox test suite, so applied to
for-next.

I did not put this in -rc or cc stable since it seems like it should
have more testing

Jason