[PATCH] Bluetooth: RFCOMM: Validate MTU in rfcomm_apply_pn() to prevent infinite loop

[PATCH] Bluetooth: RFCOMM: Validate MTU in rfcomm_apply_pn() to prevent infinite loop

[Hyunwoo Kim]

rfcomm_apply_pn() accepts the MTU value from a remote PN (Parameter
Negotiation) frame without checking for zero. When the remote peer
sends an MTU of zero, d->mtu is set to 0. This causes the sendmsg
path to enter an infinite loop when fragmenting data, as each fragment
has size == min_t(size_t, len, 0) == 0, so the remaining length never
decreases. The infinite allocation of zero-length skbs exhausts all
system memory.

Fix by clamping d->mtu to RFCOMM_DEFAULT_MTU when the negotiated
value is zero, consistent with the initial value assigned in
rfcomm_dlc_alloc().

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Hyunwoo Kim <imv4bel@gmail.com>
---
 net/bluetooth/rfcomm/core.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/net/bluetooth/rfcomm/core.c b/net/bluetooth/rfcomm/core.c
index 611a9a94151e..f9b428b1f1c8 100644
--- a/net/bluetooth/rfcomm/core.c
+++ b/net/bluetooth/rfcomm/core.c
@@ -1423,6 +1423,10 @@ static int rfcomm_apply_pn(struct rfcomm_dlc *d, int cr, struct rfcomm_pn *pn)
 
 	d->mtu = __le16_to_cpu(pn->mtu);
 
+	/* MTU 0 causes an infinite loop when fragmenting in sendmsg */
+	if (!d->mtu)
+		d->mtu = RFCOMM_DEFAULT_MTU;
+
 	if (cr && d->mtu > s->mtu)
 		d->mtu = s->mtu;
 
-- 
2.43.0

RE: Bluetooth: RFCOMM: Validate MTU in rfcomm_apply_pn() to prevent infinite loop

[bluez.test.bot]

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This is automated email and please do not reply to this email!

Dear submitter,

Thank you for submitting the patches to the linux bluetooth mailing list.
This is a CI test results with your patch series:
PW Link:https://patchwork.kernel.org/project/bluetooth/list/?series=1069345

---Test result---

Test Summary:
CheckPatch                    PENDING   0.48 seconds
GitLint                       PENDING   0.33 seconds
SubjectPrefix                 PASS      0.09 seconds
BuildKernel                   PASS      26.83 seconds
CheckAllWarning               PASS      29.62 seconds
CheckSparse                   PASS      28.26 seconds
BuildKernel32                 PASS      26.29 seconds
TestRunnerSetup               PASS      577.55 seconds
TestRunner_l2cap-tester       PASS      28.22 seconds
TestRunner_iso-tester         FAIL      31.50 seconds
TestRunner_bnep-tester        PASS      6.50 seconds
TestRunner_mgmt-tester        FAIL      116.17 seconds
TestRunner_rfcomm-tester      PASS      9.57 seconds
TestRunner_sco-tester         FAIL      14.52 seconds
TestRunner_ioctl-tester       PASS      10.52 seconds
TestRunner_mesh-tester        FAIL      12.56 seconds
TestRunner_smp-tester         PASS      8.64 seconds
TestRunner_userchan-tester    PASS      6.93 seconds
IncrementalBuild              PENDING   0.95 seconds

Details
##############################
Test: CheckPatch - PENDING
Desc: Run checkpatch.pl script
Output:

##############################
Test: GitLint - PENDING
Desc: Run gitlint
Output:

##############################
Test: TestRunner_iso-tester - FAIL
Desc: Run iso-tester with test-runner
Output:
BUG: KASAN: slab-use-after-free in le_read_features_complete+0x7e/0x2b0
Total: 141, Passed: 141 (100.0%), Failed: 0, Not Run: 0
##############################
Test: TestRunner_mgmt-tester - FAIL
Desc: Run mgmt-tester with test-runner
Output:
Total: 494, Passed: 489 (99.0%), Failed: 1, Not Run: 4

Failed Test Cases
Read Exp Feature - Success                           Failed       0.109 seconds
##############################
Test: TestRunner_sco-tester - FAIL
Desc: Run sco-tester with test-runner
Output:
WARNING: possible circular locking dependency detected
BUG: sleeping function called from invalid context at net/core/sock.c:3782
Total: 30, Passed: 30 (100.0%), Failed: 0, Not Run: 0
##############################
Test: TestRunner_mesh-tester - FAIL
Desc: Run mesh-tester with test-runner
Output:
Total: 10, Passed: 8 (80.0%), Failed: 2, Not Run: 0

Failed Test Cases
Mesh - Send cancel - 1                               Timed out    2.614 seconds
Mesh - Send cancel - 2                               Timed out    1.994 seconds
##############################
Test: IncrementalBuild - PENDING
Desc: Incremental build with the patches in the series
Output:



---
Regards,
Linux Bluetooth