Re: [PATCH] net: ipv4: fix memory leak in netlbl_cipsov4_add_std

On Mon, Jun 7, 2021 at 10:31 PM Dongliang Mu [off-list ref] wrote:

On Tue, Jun 8, 2021 at 9:57 AM Paul Moore [off-list ref] wrote:

quoted

On Mon, Jun 7, 2021 at 9:19 PM Nanyong Sun [off-list ref] wrote:

quoted

Reported by syzkaller:
BUG: memory leak
unreferenced object 0xffff888105df7000 (size 64):
comm "syz-executor842", pid 360, jiffies 4294824824 (age 22.546s)
hex dump (first 32 bytes):
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
backtrace:
[<00000000e67ed558>] kmalloc include/linux/slab.h:590 [inline]
[<00000000e67ed558>] kzalloc include/linux/slab.h:720 [inline]
[<00000000e67ed558>] netlbl_cipsov4_add_std net/netlabel/netlabel_cipso_v4.c:145 [inline]
[<00000000e67ed558>] netlbl_cipsov4_add+0x390/0x2340 net/netlabel/netlabel_cipso_v4.c:416
[<0000000006040154>] genl_family_rcv_msg_doit.isra.0+0x20e/0x320 net/netlink/genetlink.c:739
[<00000000204d7a1c>] genl_family_rcv_msg net/netlink/genetlink.c:783 [inline]
[<00000000204d7a1c>] genl_rcv_msg+0x2bf/0x4f0 net/netlink/genetlink.c:800
[<00000000c0d6a995>] netlink_rcv_skb+0x134/0x3d0 net/netlink/af_netlink.c:2504
[<00000000d78b9d2c>] genl_rcv+0x24/0x40 net/netlink/genetlink.c:811
[<000000009733081b>] netlink_unicast_kernel net/netlink/af_netlink.c:1314 [inline]
[<000000009733081b>] netlink_unicast+0x4a0/0x6a0 net/netlink/af_netlink.c:1340
[<00000000d5fd43b8>] netlink_sendmsg+0x789/0xc70 net/netlink/af_netlink.c:1929
[<000000000a2d1e40>] sock_sendmsg_nosec net/socket.c:654 [inline]
[<000000000a2d1e40>] sock_sendmsg+0x139/0x170 net/socket.c:674
[<00000000321d1969>] ____sys_sendmsg+0x658/0x7d0 net/socket.c:2350
[<00000000964e16bc>] ___sys_sendmsg+0xf8/0x170 net/socket.c:2404
[<000000001615e288>] __sys_sendmsg+0xd3/0x190 net/socket.c:2433
[<000000004ee8b6a5>] do_syscall_64+0x37/0x90 arch/x86/entry/common.c:47
[<00000000171c7cee>] entry_SYSCALL_64_after_hwframe+0x44/0xae

The memory of doi_def->map.std pointing is allocated in
netlbl_cipsov4_add_std, but no place has freed it. It should be
freed in cipso_v4_doi_free which frees the cipso DOI resource.

Fixes: 96cb8e3313c7a ("[NetLabel]: CIPSOv4 and Unlabeled packet integration")
Reported-by: Hulk Robot <redacted>
Signed-off-by: Nanyong Sun <redacted>
---
 net/ipv4/cipso_ipv4.c | 1 +
 1 file changed, 1 insertion(+)

Nice catch, thanks for fixing this.

Acked-by: Paul Moore <paul@paul-moore.com>

quoted

diff --git a/net/ipv4/cipso_ipv4.c b/net/ipv4/cipso_ipv4.c
index d6e3a92841e3..099259fc826a 100644
--- a/net/ipv4/cipso_ipv4.c
+++ b/net/ipv4/cipso_ipv4.c

@@ -471,6 +471,7 @@ void cipso_v4_doi_free(struct cipso_v4_doi *doi_def)
                kfree(doi_def->map.std->lvl.local);
                kfree(doi_def->map.std->cat.cipso);
                kfree(doi_def->map.std->cat.local);
+               kfree(doi_def->map.std);
                break;
        }
        kfree(doi_def);

Hi kernel developers,

I doubt this patch may cause invalid free in other functions where
map.std is not allocated or initialized, such as
netlbl_cipsov4_add_local, netlbl_cipsov4_add_pass.

It isn't perfectly clear to me if you are implying there is a problem
with the proposed patch or not, so I thought it might help to try and
add some clarity.

The patch above frees the cipso_v4_doi->map.std field, which is only
valid when the cipso_v4_doi->type field is equal to
CIPSO_V4_MAP_TRANS.  This is why the cipso_v4_doi_free() function
checks the type field before freeing the cipso_v4_doi->map related
fields, and why the proposed patch places the new kfree() inside that
conditional code block.

If we look at netlalbel_cipsov4_add_pass() we see that the first thing
it does after allocating a cipso_v4_doi struct is to set the type
field to CIPSO_V4_MAP_PASS.  Any calls to cipso_v4_doi_free after this
point will not end up calling the proposed kfree() addition due to the
cipso_v4_doi->type check.

We see something very similar with netlbl_cipsov4_add_local(),
although in this case the type field is set to CIPSO_V4_MAP_LOCAL.
This type value will also not trigger the proposed kfree().

If you are aware of any other potential issues with this patch please
do let us know, but from what I can see, the two concerns you
presented here are not problems with the current or proposed code.

-- 
paul moore
www.paul-moore.com