2020-06-22 11:17:44

by Zheng Bin

Subject: [PATCH v3] nbd: Fix memory leak in nbd_add_socket

When adding first socket to nbd, if nsock's allocation failed, the data
structure member "config->socks" was reallocated, but the data structure
member "config->num_connections" was not updated. A memory leak will occur
then because the function "nbd_config_put" will free "config->socks" only
when "config->num_connections" is not zero.

Fixes: 03bf73c315ed ("nbd: prevent memory leak")
Signed-off-by: Zheng Bin <[email protected]>
---

v1->v2: improve change description
v2->v3: fix some code style issues, improve change description, thanks to
Markus for the review.

drivers/block/nbd.c | 25 +++++++++++++++----------
1 file changed, 15 insertions(+), 10 deletions(-)

diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
index 43cff01a5a67..ce7e9f223b20 100644
--- a/drivers/block/nbd.c
+++ b/drivers/block/nbd.c
@@ -1033,25 +1033,26 @@ static int nbd_add_socket(struct nbd_device *nbd, unsigned long arg,
test_bit(NBD_RT_BOUND, &config->runtime_flags))) {
dev_err(disk_to_dev(nbd->disk),
"Device being setup by another task");
- sockfd_put(sock);
- return -EBUSY;
+ err = -EBUSY;
+ goto put_socket;
+ }
+
+ nsock = kzalloc(sizeof(*nsock), GFP_KERNEL);
+ if (!nsock) {
+ err = -ENOMEM;
+ goto put_socket;
}

socks = krealloc(config->socks, (config->num_connections + 1) *
sizeof(struct nbd_sock *), GFP_KERNEL);
if (!socks) {
- sockfd_put(sock);
- return -ENOMEM;
+ kfree(nsock);
+ err = -ENOMEM;
+ goto put_socket;
}

config->socks = socks;

- nsock = kzalloc(sizeof(struct nbd_sock), GFP_KERNEL);
- if (!nsock) {
- sockfd_put(sock);
- return -ENOMEM;
- }
-
nsock->fallback_index = -1;
nsock->dead = false;
mutex_init(&nsock->tx_lock);
@@ -1063,6 +1064,10 @@ static int nbd_add_socket(struct nbd_device *nbd, unsigned long arg,
atomic_inc(&config->live_connections);

return 0;
+
+put_socket:
+ sockfd_put(sock);
+ return err;
}

static int nbd_reconnect_socket(struct nbd_device *nbd, unsigned long arg)
--
2.26.0.106.g9fadedd

2020-06-22 14:29:34

by Markus Elfring

Subject: Re: [PATCH v3] nbd: Fix memory leak in nbd_add_socket

> When adding first socket to nbd, 

…

Can the term “network block device” matter for this change description?


> … A memory leak will occur
> then because the function "nbd_config_put" will free "config->socks" only
> when "config->num_connections" is not zero.

Will an additional imperative wording be helpful for the commit message?
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/process/submitting-patches.rst?id=625d3449788f85569096780592549d0340e9c0c7#n151

Regards,
Markus


…
> +++ b/drivers/block/nbd.c
> @@ -1033,25 +1033,26 @@ static int nbd_add_socket(struct nbd_device *nbd, unsigned long arg,
…
> + if (!nsock) {
> + err = -ENOMEM;
> + goto put_socket;
> }
…
> return 0;
> +

I find that the exception handling can be improved a bit more
by adding another jump target.

+e_nomem:
+ err = -ENOMEM;


> +put_socket:
> + sockfd_put(sock);
> + return err;
> }

Would you like to apply any further fine-tuning?

Regards,
Markus