Dan Carpenter
2021-Jun-14 10:43 UTC
[Nouveau] [PATCH] drm/nouveau/core/object: fix double free on error in nvkm_ioctl_new()
If nvkm_object_init() fails then we should not call nvkm_object_fini()
because it results in calling object->func->fini(object, suspend) twice.
Once inside the nvkm_object_init() function and once inside the
nvkm_object_fini() function.
Fixes: fbd58ebda9c8 ("drm/nouveau/object: merge with handle")
Signed-off-by: Dan Carpenter <dan.carpenter at oracle.com>
---
This is something that I spotted while looking for reference counting
bugs. I have tried running it, but it does not fix my crashes. My
system is basically unusable. It's something to do with the new version
of Firefox which triggers the refcount_t underflow, but switching to
Epiphany doesn't solve the issue either.
drivers/gpu/drm/nouveau/nvkm/core/ioctl.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/gpu/drm/nouveau/nvkm/core/ioctl.c
b/drivers/gpu/drm/nouveau/nvkm/core/ioctl.c
index d777df5a64e6..87c761fb475a 100644
--- a/drivers/gpu/drm/nouveau/nvkm/core/ioctl.c
+++ b/drivers/gpu/drm/nouveau/nvkm/core/ioctl.c
@@ -134,8 +134,8 @@ nvkm_ioctl_new(struct nvkm_client *client,
return 0;
}
ret = -EEXIST;
+ nvkm_object_fini(object, false);
}
- nvkm_object_fini(object, false);
}
nvkm_object_del(&object);
--
2.30.2
Dan Carpenter
2021-Jun-14 11:05 UTC
[Nouveau] [PATCH] drm/nouveau/core/object: fix double free on error in nvkm_ioctl_new()
On Mon, Jun 14, 2021 at 01:43:27PM +0300, Dan Carpenter wrote:> If nvkm_object_init() fails then we should not call nvkm_object_fini() > because it results in calling object->func->fini(object, suspend) twice. > Once inside the nvkm_object_init() function and once inside the > nvkm_object_fini() function. > > Fixes: fbd58ebda9c8 ("drm/nouveau/object: merge with handle") > Signed-off-by: Dan Carpenter <dan.carpenter at oracle.com> > --- > This is something that I spotted while looking for reference counting > bugs. I have tried running it, but it does not fix my crashes. My > system is basically unusable. It's something to do with the new version > of Firefox which triggers the refcount_t underflow, but switching to > Epiphany doesn't solve the issue either. > > drivers/gpu/drm/nouveau/nvkm/core/ioctl.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/gpu/drm/nouveau/nvkm/core/ioctl.c b/drivers/gpu/drm/nouveau/nvkm/core/ioctl.c > index d777df5a64e6..87c761fb475a 100644 > --- a/drivers/gpu/drm/nouveau/nvkm/core/ioctl.c > +++ b/drivers/gpu/drm/nouveau/nvkm/core/ioctl.c > @@ -134,8 +134,8 @@ nvkm_ioctl_new(struct nvkm_client *client, > return 0; > } > ret = -EEXIST; > + nvkm_object_fini(object, false); > } > - nvkm_object_fini(object, false); > }Hm... There is probably another bug here. drivers/gpu/drm/nouveau/nvkm/core/ioctl.c 118 } while (oclass.base.oclass != args->v0.oclass); 119 120 if (oclass.engine) { 121 oclass.engine = nvkm_engine_ref(oclass.engine); 122 if (IS_ERR(oclass.engine)) 123 return PTR_ERR(oclass.engine); 124 } 125 126 ret = oclass.ctor(&oclass, data, size, &object); ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 127 nvkm_engine_unref(&oclass.engine); 128 if (ret == 0) { 129 ret = nvkm_object_init(object); 130 if (ret == 0) { 131 list_add(&object->head, &parent->tree); 132 if (nvkm_object_insert(object)) { 133 client->data = object; 134 return 0; 135 } 136 ret = -EEXIST; 137 nvkm_object_fini(object, false); 138 } 139 } 140 141 nvkm_object_del(&object); This calls .dtor() whether or not .ctor succeeded. This error handling is written sort of unconventionally, where it checks for success and has nested success blocks but it's more normal to use gotos and keep the success path at indent level 1. a = alloc(); if (fail) return ret; b = alloc(); if (fail) goto free_a; c = alloc(); if (fail) goto free_b; return 0; free_b: free(b); free_a: free(a); return ret; It looks sort of like this if you highlight the success path vs the fail path: success success fail success success fail fail success Then if you want to read what the function does in the ideal case, you just read the 1 tab indented code. Otherwise here we'd have to add another indent level. No, wait, we can actually just move the nvkm_object_del() into the curly braces... I'll test that out and send the patch if it works. Probably I'll send the patch regardless of whether it works or not because I think it's the right thing to do. ;) regards, dan carpenter
Dan Carpenter
2021-Jun-17 11:32 UTC
[Nouveau] [PATCH] drm/nouveau/core/object: fix double free on error in nvkm_ioctl_new()
On Mon, Jun 14, 2021 at 01:43:27PM +0300, Dan Carpenter wrote:> If nvkm_object_init() fails then we should not call nvkm_object_fini() > because it results in calling object->func->fini(object, suspend) twice. > Once inside the nvkm_object_init() function and once inside the > nvkm_object_fini() function. > > Fixes: fbd58ebda9c8 ("drm/nouveau/object: merge with handle") > Signed-off-by: Dan Carpenter <dan.carpenter at oracle.com> > --- > This is something that I spotted while looking for reference counting > bugs. I have tried running it, but it does not fix my crashes. My > system is basically unusable. It's something to do with the new version > of Firefox which triggers the refcount_t underflow, but switching to > Epiphany doesn't solve the issue either. > > drivers/gpu/drm/nouveau/nvkm/core/ioctl.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/gpu/drm/nouveau/nvkm/core/ioctl.c b/drivers/gpu/drm/nouveau/nvkm/core/ioctl.c > index d777df5a64e6..87c761fb475a 100644 > --- a/drivers/gpu/drm/nouveau/nvkm/core/ioctl.c > +++ b/drivers/gpu/drm/nouveau/nvkm/core/ioctl.c > @@ -134,8 +134,8 @@ nvkm_ioctl_new(struct nvkm_client *client, > return 0; > } > ret = -EEXIST; > + nvkm_object_fini(object, false); > } > - nvkm_object_fini(object, false);Actually calling nvkm_object_fini() is probably fine. It just screws around with the registers and it's probably fine if we do that twice. Calling .dtor() when .ctor() fails is actually required because .ctor doesn't clean up after itself. So this patch is not required. The other patch is required. https://lore.kernel.org/nouveau/YMinJwpIei9n1Pn1 at mwanda/T/ In the end, I had to give up on fixing the hang and downgrade to debian's long term support version of firefox. regards, dan carpenter