[PATCH] Bluetooth: L2CAP: accept zero as a special value for MTU auto-selection

[PATCH] Bluetooth: L2CAP: accept zero as a special value for MTU auto-selection

[Fedor Pchelkin]

One of the possible ways to enable the input MTU auto-selection for L2CAP
connections is supposed to be through passing a special "0" value for it
as a socket option. Commit [1] added one of those into avdtp. However, it
simply wouldn't work because the kernel still treats the specified value
as invalid and denies the setting attempt. Recorded BlueZ logs include the
following: 

  bluetoothd[496]: profiles/audio/avdtp.c:l2cap_connect() setsockopt(L2CAP_OPTIONS): Invalid argument (22)

[1]: https://github.com/bluez/bluez/commit/ae5be371a9f53fed33d2b34748a95a5498fd4b77

Found by Linux Verification Center (linuxtesting.org).

Fixes: 4b6e228e297b ("Bluetooth: Auto tune if input MTU is set to 0")
Cc: stable@vger.kernel.org
Signed-off-by: Fedor Pchelkin <pchelkin@ispras.ru>
---
 net/bluetooth/l2cap_sock.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/bluetooth/l2cap_sock.c b/net/bluetooth/l2cap_sock.c
index 49f97d4138ea..46ea0bee2259 100644
--- a/net/bluetooth/l2cap_sock.c
+++ b/net/bluetooth/l2cap_sock.c
@@ -710,12 +710,12 @@ static bool l2cap_valid_mtu(struct l2cap_chan *chan, u16 mtu)
 {
 	switch (chan->scid) {
 	case L2CAP_CID_ATT:
-		if (mtu < L2CAP_LE_MIN_MTU)
+		if (mtu && mtu < L2CAP_LE_MIN_MTU)
 			return false;
 		break;
 
 	default:
-		if (mtu < L2CAP_DEFAULT_MIN_MTU)
+		if (mtu && mtu < L2CAP_DEFAULT_MIN_MTU)
 			return false;
 	}
 
-- 
2.39.5

Re: [PATCH] Bluetooth: L2CAP: accept zero as a special value for MTU auto-selection

[patchwork-bot+bluetooth]

Hello:

This patch was applied to bluetooth/bluetooth-next.git (master)
by Luiz Augusto von Dentz <luiz.von.dentz@intel.com>:

On Wed, 29 Jan 2025 00:08:14 +0300 you wrote:
> One of the possible ways to enable the input MTU auto-selection for L2CAP
> connections is supposed to be through passing a special "0" value for it
> as a socket option. Commit [1] added one of those into avdtp. However, it
> simply wouldn't work because the kernel still treats the specified value
> as invalid and denies the setting attempt. Recorded BlueZ logs include the
> following:
> 
> [...]

Here is the summary with links:
  - Bluetooth: L2CAP: accept zero as a special value for MTU auto-selection
    https://git.kernel.org/bluetooth/bluetooth-next/c/257a2b95631f

You are awesome, thank you!
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