CVE-2024-40910 (GCVE-0-2024-40910)
Vulnerability from cvelistv5
Published
2024-07-12 12:20
Modified
2026-08-05 11:33
Severity ?
8.8 (High) - CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Summary
In the Linux kernel, the following vulnerability has been resolved: ax25: Fix refcount imbalance on inbound connections When releasing a socket in ax25_release(), we call netdev_put() to decrease the refcount on the associated ax.25 device. However, the execution path for accepting an incoming connection never calls netdev_hold(). This imbalance leads to refcount errors, and ultimately to kernel crashes. A typical call trace for the above situation will start with one of the following errors: refcount_t: decrement hit 0; leaking memory. refcount_t: underflow; use-after-free. And will then have a trace like: Call Trace: <TASK> ? show_regs+0x64/0x70 ? __warn+0x83/0x120 ? refcount_warn_saturate+0xb2/0x100 ? report_bug+0x158/0x190 ? prb_read_valid+0x20/0x30 ? handle_bug+0x3e/0x70 ? exc_invalid_op+0x1c/0x70 ? asm_exc_invalid_op+0x1f/0x30 ? refcount_warn_saturate+0xb2/0x100 ? refcount_warn_saturate+0xb2/0x100 ax25_release+0x2ad/0x360 __sock_release+0x35/0xa0 sock_close+0x19/0x20 [...] On reboot (or any attempt to remove the interface), the kernel gets stuck in an infinite loop: unregister_netdevice: waiting for ax0 to become free. Usage count = 0 This patch corrects these issues by ensuring that we call netdev_hold() and ax25_dev_hold() for new connections in ax25_accept(). This makes the logic leading to ax25_accept() match the logic for ax25_bind(): in both cases we increment the refcount, which is ultimately decremented in ax25_release().
References
Impacted products
Vendor Product Version
Linux Linux Version: 9fd75b66b8f68498454d685dc4ba13192ae069b0
Version: 9fd75b66b8f68498454d685dc4ba13192ae069b0
Version: 9fd75b66b8f68498454d685dc4ba13192ae069b0
Version: 9fd75b66b8f68498454d685dc4ba13192ae069b0
Version: c44a453ffe16eb08acdc6129ac4fa0192dbc0456
Version: de55a1338e6a48ff1e41ea8db1432496fbe2a62b
Version: 9e1e088a57c23251f1cfe9601bbd90ade2ea73b9
Version: b20a5ab0f5fb175750c6bafd4cf12daccf00c738
Version: 452ae92b99062d2f6a34324eaf705a3b7eac9f8b
Version: 534156dd4ed768e30a43de0036f45dca7c54818f
Version: 4.14.277   ≤
Version: 4.19.240   ≤
Version: 5.4.190   ≤
Version: 5.10.112   ≤
Version: 5.15.35   ≤
Version: 5.17.2   ≤
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              "value": "AV:A - The imbalance is created by an inbound SABM processed in `ax25_rcv()`, reached from the link-layer handlers `ax25_kiss_rcv()` (RF/KISS TNC, 6pack, scc) and `bpq_rcv()` (AX.25 encapsulated in Ethernet, ethertype 0x08FF), so any station on the shared radio channel or the local Ethernet segment can trigger it. AX.25 frames are not IP-routable by the kernel itself, so this is adjacent rather than full network reach.\nAC:L - The attacker simply connects and disconnects repeatedly; each accepted-then-closed session deterministically drops one unheld netdev reference and one unheld ax25_dev reference, and only a couple of iterations are needed to drive `ax25_dev-\u003erefcount` to zero. No race, no memory-layout precondition, and the attacker controls the repetition count.\nPR:N - AX.25 has no authentication whatsoever \u2014 an unauthenticated remote station only needs to send a SABM to a listening callsign on a node/BBS/ax25d service. No credentials or local account on the victim are required.\nUI:N - A listening AX.25 service accepts inbound connections automatically and closes the session socket when the peer disconnects, which is exactly the release path that performs the unbalanced `netdev_put()`/`ax25_dev_put()`. No operator action is needed.\nS:U - The corruption is confined to kernel memory within the same security authority; no VM, IOMMU, or sandbox boundary is crossed.\nC:H - `ax25_dev_put()` frees the `ax25_dev` while `dev-\u003eax25_ptr` and `ax25_dev_list` still reference it, so subsequent received frames read attacker-refillable freed slab memory (`values[]`, `forward`, `sysheader`), and the netdev refcount underflow can free `struct net_device` while sockets still point at it \u2014 a use-after-free that is leverageable for kernel memory disclosure.\nI:H - The freed `ax25_dev` embeds a `timer_list` (DAMA slave timer with a function pointer) and a `list_head` that are still armed/linked, plus a `net_device *forward` used on the transmit path; reclaiming the slab yields write and control-flow-hijack primitives typical of a use-after-free.\nA:H - The commit documents kernel crashes from the refcount underflow, and on interface teardown or reboot the kernel spins forever in `unregister_netdevice: waiting for ax0 to become free. Usage count = 0` with RTNL held \u2014 a permanent, remotely inducible hang in addition to the UAF oops."
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    "datePublished": "2024-07-12T12:20:49.085Z",
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    "dateUpdated": "2026-08-05T11:33:57.773Z",
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AX.25 frames are not IP-routable by the kernel itself, so this is adjacent rather than full network reach.\\nAC:L - The attacker simply connects and disconnects repeatedly; each accepted-then-closed session deterministically drops one unheld netdev reference and one unheld ax25_dev reference, and only a couple of iterations are needed to drive `ax25_dev-\u003erefcount` to zero. No race, no memory-layout precondition, and the attacker controls the repetition count.\\nPR:N - AX.25 has no authentication whatsoever \\u2014 an unauthenticated remote station only needs to send a SABM to a listening callsign on a node/BBS/ax25d service. No credentials or local account on the victim are required.\\nUI:N - A listening AX.25 service accepts inbound connections automatically and closes the session socket when the peer disconnects, which is exactly the release path that performs the unbalanced `netdev_put()`/`ax25_dev_put()`. No operator action is needed.\\nS:U - The corruption is confined to kernel memory within the same security authority; no VM, IOMMU, or sandbox boundary is crossed.\\nC:H - `ax25_dev_put()` frees the `ax25_dev` while `dev-\u003eax25_ptr` and `ax25_dev_list` still reference it, so subsequent received frames read attacker-refillable freed slab memory (`values[]`, `forward`, `sysheader`), and the netdev refcount underflow can free `struct net_device` while sockets still point at it \\u2014 a use-after-free that is leverageable for kernel memory disclosure.\\nI:H - The freed `ax25_dev` embeds a `timer_list` (DAMA slave timer with a function pointer) and a `list_head` that are still armed/linked, plus a `net_device *forward` used on the transmit path; reclaiming the slab yields write and control-flow-hijack primitives typical of a use-after-free.\\nA:H - The commit documents kernel crashes from the refcount underflow, and on interface teardown or reboot the kernel spins forever in `unregister_netdevice: waiting for ax0 to become free. Usage count = 0` with RTNL held \\u2014 a permanent, remotely inducible hang in addition to the UAF oops.\"}]}], \"affected\": [{\"repo\": \"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\", \"vendor\": \"Linux\", \"product\": \"Linux\", \"versions\": [{\"status\": \"affected\", \"version\": \"9fd75b66b8f68498454d685dc4ba13192ae069b0\", \"lessThan\": \"f4df9d6c8d4e4c818252b0419c2165d66eabd4eb\", \"versionType\": \"git\"}, {\"status\": \"affected\", \"version\": \"9fd75b66b8f68498454d685dc4ba13192ae069b0\", \"lessThan\": \"52100fd74ad07b53a4666feafff1cd11436362d3\", \"versionType\": \"git\"}, {\"status\": \"affected\", \"version\": \"9fd75b66b8f68498454d685dc4ba13192ae069b0\", \"lessThan\": \"a723a6c8d4831cc8e2c7b0c9f3f0c010d4671964\", \"versionType\": \"git\"}, {\"status\": \"affected\", \"version\": \"9fd75b66b8f68498454d685dc4ba13192ae069b0\", \"lessThan\": \"3c34fb0bd4a4237592c5ecb5b2e2531900c55774\", \"versionType\": \"git\"}, {\"status\": \"affected\", \"version\": \"c44a453ffe16eb08acdc6129ac4fa0192dbc0456\", \"versionType\": \"git\"}, {\"status\": \"affected\", \"version\": \"de55a1338e6a48ff1e41ea8db1432496fbe2a62b\", \"versionType\": \"git\"}, {\"status\": \"affected\", \"version\": \"9e1e088a57c23251f1cfe9601bbd90ade2ea73b9\", \"versionType\": \"git\"}, {\"status\": \"affected\", \"version\": \"b20a5ab0f5fb175750c6bafd4cf12daccf00c738\", \"versionType\": \"git\"}, {\"status\": \"affected\", \"version\": \"452ae92b99062d2f6a34324eaf705a3b7eac9f8b\", \"versionType\": \"git\"}, {\"status\": \"affected\", \"version\": \"534156dd4ed768e30a43de0036f45dca7c54818f\", \"versionType\": \"git\"}, {\"status\": \"affected\", \"version\": \"4.14.277\", \"lessThan\": \"4.15\", \"versionType\": \"semver\"}, {\"status\": \"affected\", \"version\": \"4.19.240\", \"lessThan\": \"4.20\", \"versionType\": \"semver\"}, {\"status\": \"affected\", \"version\": \"5.4.190\", \"lessThan\": \"5.5\", \"versionType\": \"semver\"}, {\"status\": \"affected\", \"version\": \"5.10.112\", \"lessThan\": \"5.11\", \"versionType\": \"semver\"}, {\"status\": \"affected\", \"version\": \"5.15.35\", \"lessThan\": \"5.16\", \"versionType\": \"semver\"}, {\"status\": \"affected\", \"version\": \"5.17.2\", \"lessThan\": \"5.18\", \"versionType\": \"semver\"}], \"programFiles\": [\"net/ax25/af_ax25.c\"], \"defaultStatus\": \"unaffected\"}, {\"repo\": \"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\", \"vendor\": \"Linux\", \"product\": \"Linux\", \"versions\": [{\"status\": \"affected\", \"version\": \"5.18\"}, {\"status\": \"unaffected\", \"version\": \"0\", \"lessThan\": \"5.18\", \"versionType\": \"semver\"}, {\"status\": \"unaffected\", \"version\": \"6.1.95\", \"versionType\": \"semver\", \"lessThanOrEqual\": \"6.1.*\"}, {\"status\": \"unaffected\", \"version\": \"6.6.35\", \"versionType\": \"semver\", \"lessThanOrEqual\": \"6.6.*\"}, {\"status\": \"unaffected\", \"version\": \"6.9.6\", \"versionType\": \"semver\", \"lessThanOrEqual\": \"6.9.*\"}, {\"status\": \"unaffected\", \"version\": \"6.10\", \"versionType\": \"original_commit_for_fix\", \"lessThanOrEqual\": \"*\"}], \"programFiles\": [\"net/ax25/af_ax25.c\"], \"defaultStatus\": \"affected\"}], \"references\": [{\"url\": \"https://git.kernel.org/stable/c/f4df9d6c8d4e4c818252b0419c2165d66eabd4eb\"}, {\"url\": \"https://git.kernel.org/stable/c/52100fd74ad07b53a4666feafff1cd11436362d3\"}, {\"url\": \"https://git.kernel.org/stable/c/a723a6c8d4831cc8e2c7b0c9f3f0c010d4671964\"}, {\"url\": \"https://git.kernel.org/stable/c/3c34fb0bd4a4237592c5ecb5b2e2531900c55774\"}], \"x_generator\": {\"engine\": \"bippy-1.2.0\"}, \"descriptions\": [{\"lang\": \"en\", \"value\": \"In the Linux kernel, the following vulnerability has been resolved:\\n\\nax25: Fix refcount imbalance on inbound connections\\n\\nWhen releasing a socket in ax25_release(), we call netdev_put() to\\ndecrease the refcount on the associated ax.25 device. However, the\\nexecution path for accepting an incoming connection never calls\\nnetdev_hold(). This imbalance leads to refcount errors, and ultimately\\nto kernel crashes.\\n\\nA typical call trace for the above situation will start with one of the\\nfollowing errors:\\n\\n    refcount_t: decrement hit 0; leaking memory.\\n    refcount_t: underflow; use-after-free.\\n\\nAnd will then have a trace like:\\n\\n    Call Trace:\\n    \u003cTASK\u003e\\n    ? show_regs+0x64/0x70\\n    ? __warn+0x83/0x120\\n    ? refcount_warn_saturate+0xb2/0x100\\n    ? report_bug+0x158/0x190\\n    ? prb_read_valid+0x20/0x30\\n    ? handle_bug+0x3e/0x70\\n    ? exc_invalid_op+0x1c/0x70\\n    ? asm_exc_invalid_op+0x1f/0x30\\n    ? refcount_warn_saturate+0xb2/0x100\\n    ? refcount_warn_saturate+0xb2/0x100\\n    ax25_release+0x2ad/0x360\\n    __sock_release+0x35/0xa0\\n    sock_close+0x19/0x20\\n    [...]\\n\\nOn reboot (or any attempt to remove the interface), the kernel gets\\nstuck in an infinite loop:\\n\\n    unregister_netdevice: waiting for ax0 to become free. Usage count = 0\\n\\nThis patch corrects these issues by ensuring that we call netdev_hold()\\nand ax25_dev_hold() for new connections in ax25_accept(). This makes the\\nlogic leading to ax25_accept() match the logic for ax25_bind(): in both\\ncases we increment the refcount, which is ultimately decremented in\\nax25_release().\"}], \"cpeApplicability\": [{\"nodes\": [{\"negate\": false, \"cpeMatch\": [{\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"6.1.95\", \"versionStartIncluding\": \"5.18\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"6.6.35\", \"versionStartIncluding\": \"5.18\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"6.9.6\", \"versionStartIncluding\": \"5.18\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"6.10\", \"versionStartIncluding\": \"5.18\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionStartIncluding\": \"4.14.277\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionStartIncluding\": \"4.19.240\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionStartIncluding\": \"5.4.190\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionStartIncluding\": \"5.10.112\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionStartIncluding\": \"5.15.35\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionStartIncluding\": \"5.17.2\"}], \"operator\": \"OR\"}]}], \"providerMetadata\": {\"orgId\": \"416baaa9-dc9f-4396-8d5f-8c081fb06d67\", \"shortName\": \"Linux\", \"dateUpdated\": \"2026-08-05T11:33:57.773Z\"}}}",
      "cveMetadata": "{\"cveId\": \"CVE-2024-40910\", \"state\": \"PUBLISHED\", \"dateUpdated\": \"2026-08-05T11:33:57.773Z\", \"dateReserved\": \"2024-07-12T12:17:45.580Z\", \"assignerOrgId\": \"416baaa9-dc9f-4396-8d5f-8c081fb06d67\", \"datePublished\": \"2024-07-12T12:20:49.085Z\", \"assignerShortName\": \"Linux\"}",
      "dataType": "CVE_RECORD",
      "dataVersion": "5.2"
    }
  }
}


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