Messages in this thread | | | From | Christian Schoenebeck <> | Subject | Re: [PATCH v2 3/3] 9p/net: xen: fix false positive printf format overflow warning | Date | Wed, 25 Oct 2023 19:24:11 +0200 |
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On Wednesday, October 25, 2023 12:34:45 PM CEST Dominique Martinet wrote: > Use the constant to make the compiler happy about this warning: > net/9p/trans_xen.c: In function ‘xen_9pfs_front_changed’: > net/9p/trans_xen.c:444:39: warning: ‘%d’ directive writing between 1 and 11 bytes into a region of size 8 [-Wformat-overflow=] > 444 | sprintf(str, "ring-ref%d", i); > | ^~ > In function ‘xen_9pfs_front_init’, > inlined from ‘xen_9pfs_front_changed’ at net/9p/trans_xen.c:516:8, > inlined from ‘xen_9pfs_front_changed’ at net/9p/trans_xen.c:504:13: > net/9p/trans_xen.c:444:30: note: directive argument in the range [-2147483644, 2147483646] > 444 | sprintf(str, "ring-ref%d", i); > | ^~~~~~~~~~~~ > net/9p/trans_xen.c:444:17: note: ‘sprintf’ output between 10 and 20 bytes into a destination of size 16 > 444 | sprintf(str, "ring-ref%d", i); > | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > net/9p/trans_xen.c: In function ‘xen_9pfs_front_changed’: > net/9p/trans_xen.c:450:45: warning: ‘%d’ directive writing between 1 and 11 bytes into a region of size 2 [-Wformat-overflow=] > 450 | sprintf(str, "event-channel-%d", i); > | ^~ > In function ‘xen_9pfs_front_init’, > inlined from ‘xen_9pfs_front_changed’ at net/9p/trans_xen.c:516:8, > inlined from ‘xen_9pfs_front_changed’ at net/9p/trans_xen.c:504:13: > net/9p/trans_xen.c:450:30: note: directive argument in the range [-2147483644, 2147483646] > 450 | sprintf(str, "event-channel-%d", i); > | ^~~~~~~~~~~~~~~~~~ > net/9p/trans_xen.c:450:17: note: ‘sprintf’ output between 16 and 26 bytes into a destination of size 16 > 450 | sprintf(str, "event-channel-%d", i); > | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > > There is no change in logic: there only are a constant number of rings, > and there also already is a BUILD_BUG_ON that checks if that constant > goes over 9 as anything bigger would no longer fit the event-channel-%d > destination size. > > In theory having that size as part of the struct means it could be > modified by another thread and makes the compiler lose track of possible > values for 'i' here, using the constant directly here makes it work. > > Signed-off-by: Dominique Martinet <asmadeus@codewreck.org> > Message-ID: <20231023233704.1185154-4-asmadeus@codewreck.org> > ---
Reviewed-by: Christian Schoenebeck <linux_oss@crudebyte.com>
> v1->v2: > - use constant directly instead of going through a local variable > > net/9p/trans_xen.c | 15 +++++++-------- > 1 file changed, 7 insertions(+), 8 deletions(-) > > diff --git a/net/9p/trans_xen.c b/net/9p/trans_xen.c > index 1fffe2bed5b0..dfdbe1ca5338 100644 > --- a/net/9p/trans_xen.c > +++ b/net/9p/trans_xen.c > @@ -54,7 +54,6 @@ struct xen_9pfs_front_priv { > char *tag; > struct p9_client *client; > > - int num_rings; > struct xen_9pfs_dataring *rings; > }; > > @@ -131,7 +130,7 @@ static int p9_xen_request(struct p9_client *client, struct p9_req_t *p9_req) > if (list_entry_is_head(priv, &xen_9pfs_devs, list)) > return -EINVAL; > > - num = p9_req->tc.tag % priv->num_rings; > + num = p9_req->tc.tag % XEN_9PFS_NUM_RINGS; > ring = &priv->rings[num]; > > again: > @@ -279,7 +278,7 @@ static void xen_9pfs_front_free(struct xen_9pfs_front_priv *priv) > list_del(&priv->list); > write_unlock(&xen_9pfs_lock); > > - for (i = 0; i < priv->num_rings; i++) { > + for (i = 0; i < XEN_9PFS_NUM_RINGS; i++) { > struct xen_9pfs_dataring *ring = &priv->rings[i]; > > cancel_work_sync(&ring->work); > @@ -408,15 +407,14 @@ static int xen_9pfs_front_init(struct xenbus_device *dev) > if (p9_xen_trans.maxsize > XEN_FLEX_RING_SIZE(max_ring_order)) > p9_xen_trans.maxsize = XEN_FLEX_RING_SIZE(max_ring_order) / 2; > > - priv->num_rings = XEN_9PFS_NUM_RINGS; > - priv->rings = kcalloc(priv->num_rings, sizeof(*priv->rings), > + priv->rings = kcalloc(XEN_9PFS_NUM_RINGS, sizeof(*priv->rings), > GFP_KERNEL); > if (!priv->rings) { > kfree(priv); > return -ENOMEM; > } > > - for (i = 0; i < priv->num_rings; i++) { > + for (i = 0; i < XEN_9PFS_NUM_RINGS; i++) { > priv->rings[i].priv = priv; > ret = xen_9pfs_front_alloc_dataring(dev, &priv->rings[i], > max_ring_order); > @@ -434,10 +432,11 @@ static int xen_9pfs_front_init(struct xenbus_device *dev) > if (ret) > goto error_xenbus; > ret = xenbus_printf(xbt, dev->nodename, "num-rings", "%u", > - priv->num_rings); > + XEN_9PFS_NUM_RINGS); > if (ret) > goto error_xenbus; > - for (i = 0; i < priv->num_rings; i++) { > + > + for (i = 0; i < XEN_9PFS_NUM_RINGS; i++) { > char str[16]; > > BUILD_BUG_ON(XEN_9PFS_NUM_RINGS > 9); >
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