Re: [PATCH v2] virtio_blk: Fix a slient kernel panic
From: Cornelia Huck <hidden>
Date: 2016-07-18 15:21:45
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On Mon, 18 Jul 2016 22:01:29 +0800 Minfei Huang [off-list ref] wrote:
quoted hunk
We do a lot of memory allocation in function init_vq, and don't handle the allocation failure properly. Then this function will return 0, although initialization fails due to lacking memory. At that moment, kernel will panic in guest machine, if virtio is used to drive disk. To fix this bug, we should take care of allocation failure, and return correct value to let caller know what happen. Tested-by: Chao Fan <redacted> Signed-off-by: Minfei Huang <redacted> Signed-off-by: Minfei Huang <redacted> --- v1: - Refactor the patch to make code more readable --- drivers/block/virtio_blk.c | 32 +++++++++++--------------------- 1 file changed, 11 insertions(+), 21 deletions(-)diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c index 42758b5..d920512 100644 --- a/drivers/block/virtio_blk.c +++ b/drivers/block/virtio_blk.c@@ -381,9 +381,9 @@ static int init_vq(struct virtio_blk *vblk) { int err = 0; int i; - vq_callback_t **callbacks; - const char **names; - struct virtqueue **vqs; + vq_callback_t **callbacks = NULL; + const char **names = NULL; + struct virtqueue **vqs = NULL;
If you init the variables to NULL anyway...
quoted hunk
unsigned short num_vqs; struct virtio_device *vdev = vblk->vdev;@@ -394,22 +394,16 @@ static int init_vq(struct virtio_blk *vblk) num_vqs = 1;
...just do err = -ENOMEM; here and...
vblk->vqs = kmalloc(sizeof(*vblk->vqs) * num_vqs, GFP_KERNEL);
- if (!vblk->vqs) {
- err = -ENOMEM;
- goto out;
- }
+ if (!vblk->vqs)
+ return -ENOMEM;
names = kmalloc(sizeof(*names) * num_vqs, GFP_KERNEL);
- if (!names)
- goto err_names;
-
callbacks = kmalloc(sizeof(*callbacks) * num_vqs, GFP_KERNEL);
- if (!callbacks)
- goto err_callbacks;
-
vqs = kmalloc(sizeof(*vqs) * num_vqs, GFP_KERNEL);
- if (!vqs)
- goto err_vqs;
+ if (!names || !callbacks || !vqs) {
+ err = -ENOMEM;
+ goto out;
+ }...you could use the foo = kmalloc(...); if (!foo) goto out; sequence in any case. This avoids trying again and again if e.g. the names allocation already failed. Alternatively, you should be fine if you don't init the variables to NULL: The code is now either taking an early exit or setting all of the variables anyway.