GHSA-G2VJ-V28F-R7CF
Vulnerability from github – Published: 2026-05-27 12:31 – Updated: 2026-05-27 12:31In the Linux kernel, the following vulnerability has been resolved:
slip: reject VJ receive packets on instances with no rstate array
slhc_init() accepts rslots == 0 as a valid configuration, with the documented meaning of 'no receive compression'. In that case the allocation loop in slhc_init() is skipped, so comp->rstate stays NULL and comp->rslot_limit stays 0 (from the kzalloc of struct slcompress).
The receive helpers do not defend against that configuration. slhc_uncompress() dereferences comp->rstate[x] when the VJ header carries an explicit connection ID, and slhc_remember() later assigns cs = &comp->rstate[...] after only comparing the packet's slot number to comp->rslot_limit. Because rslot_limit is 0, slot 0 passes the range check, and the code dereferences a NULL rstate.
The configuration is reachable in-tree through PPP. PPPIOCSMAXCID stores its argument in a signed int, and (val >> 16) uses arithmetic shift. Passing 0xffff0000 therefore sign-extends to -1, so val2 + 1 is 0 and ppp_generic.c ends up calling slhc_init(0, 1). Because /dev/ppp open is gated by ns_capable(CAP_NET_ADMIN), the whole path is reachable from an unprivileged user namespace. Once the malformed VJ state is installed, any inbound VJ-compressed or VJ-uncompressed frame that selects slot 0 crashes the kernel in softirq context:
Oops: general protection fault, probably for non-canonical address 0xdffffc0000000000: 0000 [#1] SMP KASAN NOPTI KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007] RIP: 0010:slhc_uncompress (drivers/net/slip/slhc.c:519) Call Trace: ppp_receive_nonmp_frame (drivers/net/ppp/ppp_generic.c:2466) ppp_input (drivers/net/ppp/ppp_generic.c:2359) ppp_async_process (drivers/net/ppp/ppp_async.c:492) tasklet_action_common (kernel/softirq.c:926) handle_softirqs (kernel/softirq.c:623) run_ksoftirqd (kernel/softirq.c:1055) smpboot_thread_fn (kernel/smpboot.c:160) kthread (kernel/kthread.c:436) ret_from_fork (arch/x86/kernel/process.c:164)
Reject the receive side on such instances instead of touching rstate. slhc_uncompress() falls through to its existing 'bad' label, which bumps sls_i_error and enters the toss state. slhc_remember() mirrors that with an explicit sls_i_error increment followed by slhc_toss(); the sls_i_runt counter is not used here because a missing rstate is an internal configuration state, not a runt packet.
The transmit path is unaffected: the only in-tree caller that picks rslots from userspace (ppp_generic.c) still supplies tslots >= 1, and slip.c always calls slhc_init(16, 16), so comp->tstate remains valid and slhc_compress() continues to work.
{
"affected": [],
"aliases": [
"CVE-2026-45842"
],
"database_specific": {
"cwe_ids": [],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2026-05-27T11:16:23Z",
"severity": null
},
"details": "In the Linux kernel, the following vulnerability has been resolved:\n\nslip: reject VJ receive packets on instances with no rstate array\n\nslhc_init() accepts rslots == 0 as a valid configuration, with the\ndocumented meaning of \u0027no receive compression\u0027. In that case the\nallocation loop in slhc_init() is skipped, so comp-\u003erstate stays\nNULL and comp-\u003erslot_limit stays 0 (from the kzalloc of struct\nslcompress).\n\nThe receive helpers do not defend against that configuration.\nslhc_uncompress() dereferences comp-\u003erstate[x] when the VJ header\ncarries an explicit connection ID, and slhc_remember() later assigns\ncs = \u0026comp-\u003erstate[...] after only comparing the packet\u0027s slot number\nto comp-\u003erslot_limit. Because rslot_limit is 0, slot 0 passes the\nrange check, and the code dereferences a NULL rstate.\n\nThe configuration is reachable in-tree through PPP. PPPIOCSMAXCID\nstores its argument in a signed int, and (val \u003e\u003e 16) uses arithmetic\nshift. Passing 0xffff0000 therefore sign-extends to -1, so val2 + 1\nis 0 and ppp_generic.c ends up calling slhc_init(0, 1). Because\n/dev/ppp open is gated by ns_capable(CAP_NET_ADMIN), the whole path\nis reachable from an unprivileged user namespace. Once the malformed\nVJ state is installed, any inbound VJ-compressed or VJ-uncompressed\nframe that selects slot 0 crashes the kernel in softirq context:\n\n Oops: general protection fault, probably for non-canonical\n address 0xdffffc0000000000: 0000 [#1] SMP KASAN NOPTI\n KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007]\n RIP: 0010:slhc_uncompress (drivers/net/slip/slhc.c:519)\n Call Trace:\n \u003cTASK\u003e\n ppp_receive_nonmp_frame (drivers/net/ppp/ppp_generic.c:2466)\n ppp_input (drivers/net/ppp/ppp_generic.c:2359)\n ppp_async_process (drivers/net/ppp/ppp_async.c:492)\n tasklet_action_common (kernel/softirq.c:926)\n handle_softirqs (kernel/softirq.c:623)\n run_ksoftirqd (kernel/softirq.c:1055)\n smpboot_thread_fn (kernel/smpboot.c:160)\n kthread (kernel/kthread.c:436)\n ret_from_fork (arch/x86/kernel/process.c:164)\n \u003c/TASK\u003e\n\nReject the receive side on such instances instead of touching rstate.\nslhc_uncompress() falls through to its existing \u0027bad\u0027 label, which\nbumps sls_i_error and enters the toss state. slhc_remember() mirrors\nthat with an explicit sls_i_error increment followed by slhc_toss();\nthe sls_i_runt counter is not used here because a missing rstate is\nan internal configuration state, not a runt packet.\n\nThe transmit path is unaffected: the only in-tree caller that picks\nrslots from userspace (ppp_generic.c) still supplies tslots \u003e= 1, and\nslip.c always calls slhc_init(16, 16), so comp-\u003etstate remains valid\nand slhc_compress() continues to work.",
"id": "GHSA-g2vj-v28f-r7cf",
"modified": "2026-05-27T12:31:24Z",
"published": "2026-05-27T12:31:23Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-45842"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/7b0d9e878ec2b21d99ae8051b3dda59cdb66c152"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/9e1ff0eead073c4f46d874ad2526b7dda5465faf"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/c6980e8b1a86288167f34966fa5219031999b6f1"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/de42f86e2cf5028a97e74c25869d1a962b13c301"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/e76607442d5b73e1ba6768f501ef815bb58c2c0e"
}
],
"schema_version": "1.4.0",
"severity": []
}
Sightings
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