[PATCH] 6lowpan: fix NHC entry use-after-free on error path

[PATCH] 6lowpan: fix NHC entry use-after-free on error path

[Yizhou Zhao]

lowpan_nhc_do_uncompression() looks up an NHC descriptor while holding
lowpan_nhc_lock.  If the descriptor has no uncompress callback, the error
path drops the lock before printing nhc->name.

lowpan_nhc_del() removes descriptors under the same lock and then relies
on synchronize_net() before the owning module can be unloaded.  That only
waits for net RX RCU readers.  lowpan_header_decompress() is also exported
and can be reached from callers that are not necessarily covered by the net
core RX critical section, for example the Bluetooth 6LoWPAN L2CAP receive
path.

This leaves a race where one task drops lowpan_nhc_lock in the error path,
another task unregisters and frees the matching descriptor after
synchronize_net() returns, and the first task then dereferences nhc->name
for the warning.

With the post-unlock window widened, KASAN reports:

  BUG: KASAN: slab-use-after-free in lowpan_nhc_do_uncompression+0x1f4/0x220
  Read of size 8
  lowpan_nhc_do_uncompression
  lowpan_header_decompress

Fix this by printing the warning before dropping lowpan_nhc_lock, so the
descriptor name is read while unregister is still excluded.  The malformed
packet is still rejected with -ENOTSUPP.

Fixes: 92aa7c65d295 ("6lowpan: add generic nhc layer interface")
Cc: stable@vger.kernel.org
Reported-by: Yizhou Zhao <zhaoyz24@mails.tsinghua.edu.cn>
Reported-by: Yuxiang Yang <yangyx22@mails.tsinghua.edu.cn>
Reported-by: Ao Wang <wangao@seu.edu.cn>
Reported-by: Xuewei Feng <fengxw06@126.com>
Reported-by: Qi Li <qli01@tsinghua.edu.cn>
Reported-by: Ke Xu <xuke@tsinghua.edu.cn>
Assisted-by: GLM:GLM-5.1
Signed-off-by: Yizhou Zhao <zhaoyz24@mails.tsinghua.edu.cn>
---
diff --git a/net/6lowpan/nhc.c b/net/6lowpan/nhc.c
index 7b374595328d..a4dde85664f2 100644
--- a/net/6lowpan/nhc.c
+++ b/net/6lowpan/nhc.c
@@ -117,9 +117,9 @@ int lowpan_nhc_do_uncompression(struct sk_buff *skb,
 				return ret;
 			}
 		} else {
-			spin_unlock_bh(&lowpan_nhc_lock);
 			netdev_warn(dev, "received nhc id for %s which is not implemented.\n",
 				    nhc->name);
+			spin_unlock_bh(&lowpan_nhc_lock);
 			return -ENOTSUPP;
 		}
 	} else {

--
2.43.0

RE: 6lowpan: fix NHC entry use-after-free on error path

[bluez.test.bot]

[-- Attachment #1: Type: text/plain, Size: 4094 bytes --]

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=1108371

---Test result---

Test Summary:
CheckPatch                    FAIL      0.75 seconds
VerifyFixes                   PASS      0.13 seconds
VerifySignedoff               PASS      0.14 seconds
GitLint                       PASS      0.34 seconds
SubjectPrefix                 FAIL      0.13 seconds
BuildKernel                   PASS      28.31 seconds
CheckAllWarning               PASS      31.95 seconds
CheckSparse                   PASS      29.63 seconds
BuildKernel32                 PASS      27.13 seconds
TestRunnerSetup               PASS      596.34 seconds
TestRunner_l2cap-tester       PASS      65.08 seconds
TestRunner_iso-tester         PASS      86.94 seconds
TestRunner_bnep-tester        PASS      20.27 seconds
TestRunner_mgmt-tester        FAIL      224.52 seconds
TestRunner_rfcomm-tester      PASS      26.68 seconds
TestRunner_sco-tester         PASS      34.10 seconds
TestRunner_ioctl-tester       PASS      27.51 seconds
TestRunner_mesh-tester        FAIL      26.96 seconds
TestRunner_smp-tester         PASS      24.40 seconds
TestRunner_userchan-tester    PASS      21.02 seconds
TestRunner_6lowpan-tester     PASS      23.79 seconds
IncrementalBuild              PASS      26.60 seconds

Details
##############################
Test: CheckPatch - FAIL
Desc: Run checkpatch.pl script
Output:
6lowpan: fix NHC entry use-after-free on error path
WARNING: Reported-by: should be immediately followed by Closes: with a URL to the report
#120: 
Reported-by: Yizhou Zhao <zhaoyz24@mails.tsinghua.edu.cn>
Reported-by: Yuxiang Yang <yangyx22@mails.tsinghua.edu.cn>

WARNING: Reported-by: should be immediately followed by Closes: with a URL to the report
#121: 
Reported-by: Yuxiang Yang <yangyx22@mails.tsinghua.edu.cn>
Reported-by: Ao Wang <wangao@seu.edu.cn>

WARNING: Reported-by: should be immediately followed by Closes: with a URL to the report
#122: 
Reported-by: Ao Wang <wangao@seu.edu.cn>
Reported-by: Xuewei Feng <fengxw06@126.com>

WARNING: Reported-by: should be immediately followed by Closes: with a URL to the report
#123: 
Reported-by: Xuewei Feng <fengxw06@126.com>
Reported-by: Qi Li <qli01@tsinghua.edu.cn>

WARNING: Reported-by: should be immediately followed by Closes: with a URL to the report
#124: 
Reported-by: Qi Li <qli01@tsinghua.edu.cn>
Reported-by: Ke Xu <xuke@tsinghua.edu.cn>

WARNING: Reported-by: should be immediately followed by Closes: with a URL to the report
#125: 
Reported-by: Ke Xu <xuke@tsinghua.edu.cn>
Assisted-by: GLM:GLM-5.1

total: 0 errors, 6 warnings, 0 checks, 10 lines checked

NOTE: For some of the reported defects, checkpatch may be able to
      mechanically convert to the typical style using --fix or --fix-inplace.

/github/workspace/src/patch/14618776.patch has style problems, please review.

NOTE: Ignored message types: UNKNOWN_COMMIT_ID

NOTE: If any of the errors are false positives, please report
      them to the maintainer, see CHECKPATCH in MAINTAINERS.


##############################
Test: SubjectPrefix - FAIL
Desc: Check subject contains "Bluetooth" prefix
Output:
"Bluetooth: " prefix is not specified in the subject
##############################
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       0.265 seconds
##############################
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    2.252 seconds
Mesh - Send cancel - 2                               Timed out    1.985 seconds


https://github.com/bluez/bluetooth-next/pull/298

---
Regards,
Linux Bluetooth