[PATCH net] net: tipc: fix refcount warning in tipc_aead_encrypt

[PATCH net] net: tipc: fix refcount warning in tipc_aead_encrypt

[Charalampos Mitrodimas]

syzbot reported a refcount warning [1] caused by calling get_net() on
a network namespace that is being destroyed (refcount=0). This happens
when a TIPC discovery timer fires during network namespace cleanup.

The recently added get_net() call in commit e279024617134 ("net/tipc:
fix slab-use-after-free Read in tipc_aead_encrypt_done") attempts to
hold a reference to the network namespace. However, if the namespace
is already being destroyed, its refcount might be zero, leading to the
use-after-free warning.

Replace get_net() with maybe_get_net(), which safely checks if the
refcount is non-zero before incrementing it. If the namespace is being
destroyed, return -ENXIO early, after releasing the bearer reference.

[1]: https://lore.kernel.org/all/68342b55.a70a0220.253bc2.0091.GAE@google.com/T/#m12019cf9ae77e1954f666914640efa36d52704a2

Reported-by: syzbot+f0c4a4aba757549ae26c@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/all/68342b55.a70a0220.253bc2.0091.GAE@google.com/T/#m12019cf9ae77e1954f666914640efa36d52704a2
Fixes: e27902461713 ("net/tipc: fix slab-use-after-free Read in tipc_aead_encrypt_done")
Signed-off-by: Charalampos Mitrodimas <charmitro@posteo.net>
---
 net/tipc/crypto.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/net/tipc/crypto.c b/net/tipc/crypto.c
index 8584893b478510dc1ddda321ed06054de327609b..49916f983fe5e1d48477945104fe5fc589257533 100644
--- a/net/tipc/crypto.c
+++ b/net/tipc/crypto.c
@@ -818,7 +818,11 @@ static int tipc_aead_encrypt(struct tipc_aead *aead, struct sk_buff *skb,
 	}
 
 	/* Get net to avoid freed tipc_crypto when delete namespace */
-	get_net(aead->crypto->net);
+	if (!maybe_get_net(aead->crypto->net)) {
+		tipc_bearer_put(b);
+		rc = -ENXIO;
+		goto exit;
+	}
 
 	/* Now, do encrypt */
 	rc = crypto_aead_encrypt(req);

---
base-commit: 49fffac983ac52aea0ab94914be3f56bcf92d5dc
change-id: 20250526-net-tipc-warning-bda0aa9c5422

Best regards,
-- 
Charalampos Mitrodimas <charmitro@posteo.net>

RE: [PATCH net] net: tipc: fix refcount warning in tipc_aead_encrypt

[Tung Quang Nguyen]

>Subject: [PATCH net] net: tipc: fix refcount warning in tipc_aead_encrypt
>
>syzbot reported a refcount warning [1] caused by calling get_net() on a
>network namespace that is being destroyed (refcount=0). This happens when a
>TIPC discovery timer fires during network namespace cleanup.
>
>The recently added get_net() call in commit e279024617134 ("net/tipc:
>fix slab-use-after-free Read in tipc_aead_encrypt_done") attempts to hold a
>reference to the network namespace. However, if the namespace is already
>being destroyed, its refcount might be zero, leading to the use-after-free
>warning.
>
>Replace get_net() with maybe_get_net(), which safely checks if the refcount is
>non-zero before incrementing it. If the namespace is being destroyed, return -
>ENXIO early, after releasing the bearer reference.
>
>[1]:
>https://lore.kernel.org/all/68342b55.a70a0220.253bc2.0091.GAE@google.com
>/T/#m12019cf9ae77e1954f666914640efa36d52704a2
>
>Reported-by: syzbot+f0c4a4aba757549ae26c@syzkaller.appspotmail.com
>Closes:
>https://lore.kernel.org/all/68342b55.a70a0220.253bc2.0091.GAE@google.com
>/T/#m12019cf9ae77e1954f666914640efa36d52704a2
>Fixes: e27902461713 ("net/tipc: fix slab-use-after-free Read in
>tipc_aead_encrypt_done")
>Signed-off-by: Charalampos Mitrodimas <charmitro@posteo.net>
>---
> net/tipc/crypto.c | 6 +++++-
> 1 file changed, 5 insertions(+), 1 deletion(-)
>
>diff --git a/net/tipc/crypto.c b/net/tipc/crypto.c index
>8584893b478510dc1ddda321ed06054de327609b..49916f983fe5e1d484779451
>04fe5fc589257533 100644
>--- a/net/tipc/crypto.c
>+++ b/net/tipc/crypto.c
>@@ -818,7 +818,11 @@ static int tipc_aead_encrypt(struct tipc_aead *aead,
>struct sk_buff *skb,
> 	}
>
> 	/* Get net to avoid freed tipc_crypto when delete namespace */
>-	get_net(aead->crypto->net);
>+	if (!maybe_get_net(aead->crypto->net)) {
>+		tipc_bearer_put(b);
>+		rc = -ENXIO;
-ENODEV should be used instead as we also use it for bearer ref count. Thus, caller of tipc_aead_encrypt() does not need to care about handling new error code.
>+		goto exit;
>+	}
>
> 	/* Now, do encrypt */
> 	rc = crypto_aead_encrypt(req);

Re: [PATCH net] net: tipc: fix refcount warning in tipc_aead_encrypt

[Charalampos Mitrodimas]

Tung Quang Nguyen <tung.quang.nguyen@est.tech> writes:

>>Subject: [PATCH net] net: tipc: fix refcount warning in tipc_aead_encrypt
>>
>>syzbot reported a refcount warning [1] caused by calling get_net() on a
>>network namespace that is being destroyed (refcount=0). This happens when a
>>TIPC discovery timer fires during network namespace cleanup.
>>
>>The recently added get_net() call in commit e279024617134 ("net/tipc:
>>fix slab-use-after-free Read in tipc_aead_encrypt_done") attempts to hold a
>>reference to the network namespace. However, if the namespace is already
>>being destroyed, its refcount might be zero, leading to the use-after-free
>>warning.
>>
>>Replace get_net() with maybe_get_net(), which safely checks if the refcount is
>>non-zero before incrementing it. If the namespace is being destroyed, return -
>>ENXIO early, after releasing the bearer reference.
>>
>>[1]:
>>https://lore.kernel.org/all/68342b55.a70a0220.253bc2.0091.GAE@google.com
>>/T/#m12019cf9ae77e1954f666914640efa36d52704a2
>>
>>Reported-by: syzbot+f0c4a4aba757549ae26c@syzkaller.appspotmail.com
>>Closes:
>>https://lore.kernel.org/all/68342b55.a70a0220.253bc2.0091.GAE@google.com
>>/T/#m12019cf9ae77e1954f666914640efa36d52704a2
>>Fixes: e27902461713 ("net/tipc: fix slab-use-after-free Read in
>>tipc_aead_encrypt_done")
>>Signed-off-by: Charalampos Mitrodimas <charmitro@posteo.net>
>>---
>> net/tipc/crypto.c | 6 +++++-
>> 1 file changed, 5 insertions(+), 1 deletion(-)
>>
>>diff --git a/net/tipc/crypto.c b/net/tipc/crypto.c index
>>8584893b478510dc1ddda321ed06054de327609b..49916f983fe5e1d484779451
>>04fe5fc589257533 100644
>>--- a/net/tipc/crypto.c
>>+++ b/net/tipc/crypto.c
>>@@ -818,7 +818,11 @@ static int tipc_aead_encrypt(struct tipc_aead *aead,
>>struct sk_buff *skb,
>> 	}
>>
>> 	/* Get net to avoid freed tipc_crypto when delete namespace */
>>-	get_net(aead->crypto->net);
>>+	if (!maybe_get_net(aead->crypto->net)) {
>>+		tipc_bearer_put(b);
>>+		rc = -ENXIO;
> -ENODEV should be used instead as we also use it for bearer ref count. Thus, caller of tipc_aead_encrypt() does not need to care about handling new error code.

Hi,

Thanks for the review!

Addressed in v2.

C. Mitrodimas

>>+		goto exit;
>>+	}
>>
>> 	/* Now, do encrypt */
>> 	rc = crypto_aead_encrypt(req);