Messages in this thread | | | From | Christian Schoenebeck <> | Subject | Re: [PATCH v2] net/9p: Initialize the iounit field during fid creation | Date | Sun, 10 Jul 2022 16:48:29 +0200 |
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On Sonntag, 10. Juli 2022 16:14:02 CEST Tyler Hicks wrote: > 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 > p9_fid struct shortly after the fid is created by p9_fid_create(). On > the other hand, an XATTRWALK operation doesn't allow for the server to > specify an iounit value. The iounit field of the newly allocated p9_fid > struct remained uninitialized in that case. 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. > > Fixes: ebf46264a004 ("fs/9p: Add support user. xattr") > Cc: stable@vger.kernel.org > Signed-off-by: Tyler Hicks <tyhicks@linux.microsoft.com>
Reviewed-by: Christian Schoenebeck <linux_oss@crudebyte.com>
> --- > > v2: > - Add Fixes tag > - Improve commit message clarity to make it clear that this only affects > xattr get/set > - kzalloc() the entire fid struct instead of individually zeroing each > member > - Thanks to Christophe JAILLET for the suggestion > v1: https://lore.kernel.org/lkml/20220710062557.GA272934@sequoia/ > > net/9p/client.c | 5 +---- > 1 file changed, 1 insertion(+), 4 deletions(-) > > diff --git a/net/9p/client.c b/net/9p/client.c > index 8bba0d9cf975..371519e7b885 100644 > --- a/net/9p/client.c > +++ b/net/9p/client.c > @@ -889,16 +889,13 @@ static struct p9_fid *p9_fid_create(struct p9_client > *clnt) struct p9_fid *fid; > > p9_debug(P9_DEBUG_FID, "clnt %p\n", clnt); > - fid = kmalloc(sizeof(*fid), GFP_KERNEL); > + fid = kzalloc(sizeof(*fid), GFP_KERNEL); > if (!fid) > return NULL; > > - memset(&fid->qid, 0, sizeof(fid->qid)); > fid->mode = -1; > fid->uid = current_fsuid(); > fid->clnt = clnt; > - fid->rdir = NULL; > - fid->fid = 0; > refcount_set(&fid->count, 1); > > idr_preload(GFP_KERNEL);
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