Messages in this thread | | | Date | Sun, 10 Jul 2022 09:12:51 -0500 | From | Tyler Hicks <> | Subject | Re: [PATCH] net/9p: Initialize the iounit field during fid creation |
| |
On 2022-07-10 22:21:33, Dominique Martinet wrote: > Tyler Hicks wrote on Sat, Jul 09, 2022 at 03:00:05PM -0500: > > Ensure that the fid's iounit field is set to zero when a new fid is > > created. Certain 9P operations, such as OPEN and CREATE, allow the > > server to reply with an iounit size which the client code assigns to the > > fid struct shortly after the fid is created in p9_fid_create(). Other > > operations that follow a call to p9_fid_create(), such as an XATTRWALK, > > don't include an iounit value in the reply message from the server. In > > the latter case, the iounit field remained uninitialized. Depending on > > allocation patterns, the iounit value could have been something > > reasonable that was carried over from previously freed fids or, in the > > worst case, could have been arbitrary values from non-fid related usages > > of the memory location. > > > > The bug was detected in the Windows Subsystem for Linux 2 (WSL2) kernel > > after the uninitialized iounit field resulted in the typical sequence of > > two getxattr(2) syscalls, one to get the size of an xattr and another > > after allocating a sufficiently sized buffer to fit the xattr value, to > > hit an unexpected ERANGE error in the second call to getxattr(2). An > > uninitialized iounit field would sometimes force rsize to be smaller > > than the xattr value size in p9_client_read_once() and the 9P server in > > WSL refused to chunk up the READ on the attr_fid and, instead, returned > > ERANGE to the client. The virtfs server in QEMU seems happy to chunk up > > the READ and this problem goes undetected there. However, there are > > likely other non-xattr implications of this bug that could cause > > inefficient communication between the client and server. > > > > Cc: stable@vger.kernel.org > > Signed-off-by: Tyler Hicks <tyhicks@linux.microsoft.com> > > Thanks for the fix!
No problem!
> > > --- > > > > Note that I haven't had a chance to identify when this bug was > > introduced so I don't yet have a proper Fixes tag. The history looked a > > little tricky to me but I'll have another look in the coming days. We > > started hitting this bug after trying to move from linux-5.10.y to > > linux-5.15.y but I didn't see any obvious changes between those two > > series. I'm not confident of this theory but perhaps the fid refcounting > > changes impacted the fid allocation patterns enough to uncover the > > latent bug? > > > > net/9p/client.c | 1 + > > 1 file changed, 1 insertion(+) > > > > diff --git a/net/9p/client.c b/net/9p/client.c > > index 8bba0d9cf975..1dfceb9154f7 100644 > > --- a/net/9p/client.c > > +++ b/net/9p/client.c > > @@ -899,6 +899,7 @@ static struct p9_fid *p9_fid_create(struct p9_client *clnt) > > fid->clnt = clnt; > > fid->rdir = NULL; > > fid->fid = 0; > > + fid->iounit = 0; > > ugh, this isn't the first we've missed so I'll be tempted to agree with > Christophe -- let's make that a kzalloc and only set non-zero fields.
Agreed - This is the better approach. V2 will be sent out shortly.
Tyler
> > -- > Dominique >
| |