[RFC PATCH 0/1] Fix KASAN: slab-out-of-bounds Read in sk_psock_get

[RFC PATCH 0/1] Fix KASAN: slab-out-of-bounds Read in sk_psock_get

[Khalid Masum]

Using size of sk_psock as the size for kcm_psock_cache size no longer
reproduces the issue. There might be a better way to solve this issue
though so I would like to ask for feedback.

Reported-and-tested-by: syzbot+1fa91bcd05206ff8cbb5@syzkaller.appspotmail.com
Link: https://syzkaller.appspot.com/bug?extid=1fa91bcd05206ff8cbb5

Khalid Masum (1):
  net: kcm: Use sk_psock size for kcm_psock_cache

 net/kcm/kcmsock.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

-- 
2.36.1

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[RFC PATCH 1/1] net: kcm: Use sk_psock size for kcm_psock_cache

[Khalid Masum]

`struct sock` has a member `sk_user_data`, which got its memory allocated
in `kcm_attach` by `kcm_psock_cache` with the size of `kcm_psock`. Which
is not enough when the member is used as `sk_psock` causing out of bound
read.

Use `sk_psock` size to allocate memory instead for `sk_user_data`.

Reported-by: syzbot+1fa91bcd05206ff8cbb5@syzkaller.appspotmail.com
Signed-off-by: Khalid Masum <khalid.masum.92@gmail.com>
---
 net/kcm/kcmsock.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/kcm/kcmsock.c b/net/kcm/kcmsock.c
index 71899e5a5a11..688bee56f90c 100644
--- a/net/kcm/kcmsock.c
+++ b/net/kcm/kcmsock.c
@@ -23,6 +23,7 @@
 #include <linux/workqueue.h>
 #include <linux/syscalls.h>
 #include <linux/sched/signal.h>
+#include <linux/skmsg.h>
 
 #include <net/kcm.h>
 #include <net/netns/generic.h>
@@ -2041,7 +2042,7 @@ static int __init kcm_init(void)
 		goto fail;
 
 	kcm_psockp = kmem_cache_create("kcm_psock_cache",
-				       sizeof(struct kcm_psock), 0,
+				       sizeof(struct sk_psock), 0,
 					SLAB_HWCACHE_ALIGN, NULL);
 	if (!kcm_psockp)
 		goto fail;
-- 
2.36.1

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Re: [RFC PATCH 1/1] net: kcm: Use sk_psock size for kcm_psock_cache

[Greg KH]

On Wed, Jul 13, 2022 at 12:32:04PM +0600, Khalid Masum wrote:
> `struct sock` has a member `sk_user_data`, which got its memory allocated
> in `kcm_attach` by `kcm_psock_cache` with the size of `kcm_psock`. Which
> is not enough when the member is used as `sk_psock` causing out of bound
> read.
> 
> Use `sk_psock` size to allocate memory instead for `sk_user_data`.
> 
> Reported-by: syzbot+1fa91bcd05206ff8cbb5@syzkaller.appspotmail.com
> Signed-off-by: Khalid Masum <khalid.masum.92@gmail.com>
> ---
>  net/kcm/kcmsock.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)

What commit id does this fix?

thanks,

greg k-h
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Re: [RFC PATCH 1/1] net: kcm: Use sk_psock size for kcm_psock_cache

[Jakub Kicinski]

On Wed, 13 Jul 2022 12:32:04 +0600 Khalid Masum wrote:
> `struct sock` has a member `sk_user_data`, which got its memory allocated
> in `kcm_attach` by `kcm_psock_cache` with the size of `kcm_psock`. Which
> is not enough when the member is used as `sk_psock` causing out of bound
> read.
> 
> Use `sk_psock` size to allocate memory instead for `sk_user_data`.
> 
> Reported-by: syzbot+1fa91bcd05206ff8cbb5@syzkaller.appspotmail.com
> Signed-off-by: Khalid Masum <khalid.masum.92@gmail.com>

Odd CC list, it looks like a netdev problem but netdev@ is not copied.

We had an other parson looking at this on netdev. Is this happening
when legit kernel socket gets mixed with BPF sockmap?

Does this fix work?

https://lore.kernel.org/netdev/165030056960.5073.6664402939918720250.stgit@oracle-102.nfsv4.dev/
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Re: [RFC PATCH 1/1] net: kcm: Use sk_psock size for kcm_psock_cache

[Khalid Masum]

On Thu, Jul 14, 2022 at 12:16 AM Jakub Kicinski <kuba@kernel.org> wrote:
>
> On Wed, 13 Jul 2022 12:32:04 +0600 Khalid Masum wrote:
> > `struct sock` has a member `sk_user_data`, which got its memory allocated
> > in `kcm_attach` by `kcm_psock_cache` with the size of `kcm_psock`. Which
> > is not enough when the member is used as `sk_psock` causing out of bound
> > read.
> >
> > Use `sk_psock` size to allocate memory instead for `sk_user_data`.
> >
> > Reported-by: syzbot+1fa91bcd05206ff8cbb5@syzkaller.appspotmail.com
> > Signed-off-by: Khalid Masum <khalid.masum.92@gmail.com>
>
> Odd CC list, it looks like a netdev problem but netdev@ is not copied.

I am sorry for the inconvenience. I resent the patch with netdev in CC here:
https://lore.kernel.org/netdev/20220713181324.14228-2-khalid.masum.92@gmail.com/

> We had an other parson looking at this on netdev. Is this happening
> when legit kernel socket gets mixed with BPF sockmap?
>
> Does this fix work?
I will take a look at it.
> https://lore.kernel.org/netdev/165030056960.5073.6664402939918720250.stgit@oracle-102.nfsv4.dev/

Thanks,
Khalid Masum
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[RFC PATCH 1/1] net: kcm: Use sk_psock size for kcm_psock_cache

[Khalid Masum]

`struct sock` has a member `sk_user_data`, which got its memory allocated
in `kcm_attach` by `kcm_psock_cache` with the size of `kcm_psock`. Which
is not enough when the member is used as `sk_psock` causing out of bound
read.

Use `sk_psock` size to allocate memory instead for `sk_user_data`.

Reported-by: syzbot+1fa91bcd05206ff8cbb5@syzkaller.appspotmail.com
Link: https://syzkaller.appspot.com/bug?extid=1fa91bcd05206ff8cbb5
Signed-off-by: Khalid Masum <khalid.masum.92@gmail.com>

---
 net/kcm/kcmsock.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/kcm/kcmsock.c b/net/kcm/kcmsock.c
index 71899e5a5a11..688bee56f90c 100644
--- a/net/kcm/kcmsock.c
+++ b/net/kcm/kcmsock.c
@@ -23,6 +23,7 @@
 #include <linux/workqueue.h>
 #include <linux/syscalls.h>
 #include <linux/sched/signal.h>
+#include <linux/skmsg.h>
 
 #include <net/kcm.h>
 #include <net/netns/generic.h>
@@ -2041,7 +2042,7 @@ static int __init kcm_init(void)
 		goto fail;
 
 	kcm_psockp = kmem_cache_create("kcm_psock_cache",
-				       sizeof(struct kcm_psock), 0,
+				       sizeof(struct sk_psock), 0,
 					SLAB_HWCACHE_ALIGN, NULL);
 	if (!kcm_psockp)
 		goto fail;
-- 
2.36.1

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