GHSA-XWC4-2QQP-PXH3
Vulnerability from github – Published: 2026-09-11 21:31 – Updated: 2026-09-13 09:32In the Linux kernel, the following vulnerability has been resolved:
SUNRPC: fix gssx_dec_option_array error path bugs
Four coupled defects in the gssx XDR option-array decoder make the error paths unsafe: a NULL deref in the caller, a refcount leak on the decoded group_info, and a latent use-after-free that the leak fix would otherwise expose.
gssx_dec_option_array() sets oa->count = 1 before allocating oa->data. If that allocation fails, -ENOMEM is returned with oa->count == 1 and oa->data == NULL. All other error paths jump to free_oa: which frees oa->data and NULLs it but also leaves oa->count == 1. The caller trusts the count:
gssp_accept_sec_context_upcall()
gssx_dec_accept_sec_context()
gssx_dec_option_array() /* fails, count=1 data=NULL */
data = res.options.data[0].value /* NULL deref */
Independently, free_creds: releases the partially decoded svc_cred with a bare kfree(creds). gssx_dec_linux_creds() installs a groups_alloc() result into creds->cr_group_info; that object is kvmalloc-backed and refcounted, and only put_group_info() reaches kvfree(). A plain kfree(creds) drops the wrapper and leaks the group_info allocation.
The natural fix for the leak is to call free_svc_cred(creds) before kfree(creds), but free_svc_cred() invokes put_group_info() on creds->cr_group_info unconditionally when non-NULL. The existing out_free_groups: path in gssx_dec_linux_creds() already called groups_free() on that pointer without clearing it, so once free_svc_cred() is wired in, the subsequent put_group_info() would touch freed memory.
Fix all four together:
- Move the oa->count = 1 assignment below the oa->data allocation so it is never set when oa->data is NULL.
- Reset oa->count to 0 at free_oa: so count and data stay coherent and the caller sees an empty option array.
- Call free_svc_cred(creds) before kfree(creds) at free_creds: so the refcounted cr_group_info is released. free_svc_cred() either NULL-guards each field explicitly (cr_group_info has an if() check) or delegates to a helper that is NULL-safe itself (kfree for the string fields, gss_mech_put() which guards with if(gm) at gss_mech_switch.c:342), so it is safe to call on a partially decoded svc_cred where only cr_uid/cr_gid/cr_group_info have been written and everything else is zero from kzalloc.
- In gssx_dec_linux_creds()'s out_free_groups: path, release cr_group_info with put_group_info() rather than groups_free() so the teardown matches free_svc_cred()'s refcount-aware path, and clear the pointer so a later free_svc_cred() on the same creds does not release it a second time.
{
"affected": [],
"aliases": [
"CVE-2026-89544"
],
"database_specific": {
"cwe_ids": [],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2026-09-11T20:19:37Z",
"severity": "HIGH"
},
"details": "In the Linux kernel, the following vulnerability has been resolved:\n\nSUNRPC: fix gssx_dec_option_array error path bugs\n\nFour coupled defects in the gssx XDR option-array decoder make the\nerror paths unsafe: a NULL deref in the caller, a refcount leak on\nthe decoded group_info, and a latent use-after-free that the leak\nfix would otherwise expose.\n\ngssx_dec_option_array() sets oa-\u003ecount = 1 before allocating\noa-\u003edata. If that allocation fails, -ENOMEM is returned with\noa-\u003ecount == 1 and oa-\u003edata == NULL. All other error paths jump\nto free_oa: which frees oa-\u003edata and NULLs it but also leaves\noa-\u003ecount == 1. The caller trusts the count:\n\n gssp_accept_sec_context_upcall()\n gssx_dec_accept_sec_context()\n gssx_dec_option_array() /* fails, count=1 data=NULL */\n data = res.options.data[0].value /* NULL deref */\n\nIndependently, free_creds: releases the partially decoded svc_cred\nwith a bare kfree(creds). gssx_dec_linux_creds() installs a\ngroups_alloc() result into creds-\u003ecr_group_info; that object is\nkvmalloc-backed and refcounted, and only put_group_info() reaches\nkvfree(). A plain kfree(creds) drops the wrapper and leaks the\ngroup_info allocation.\n\nThe natural fix for the leak is to call free_svc_cred(creds) before\nkfree(creds), but free_svc_cred() invokes put_group_info() on\ncreds-\u003ecr_group_info unconditionally when non-NULL. The existing\nout_free_groups: path in gssx_dec_linux_creds() already called\ngroups_free() on that pointer without clearing it, so once\nfree_svc_cred() is wired in, the subsequent put_group_info() would\ntouch freed memory.\n\nFix all four together:\n\n - Move the oa-\u003ecount = 1 assignment below the oa-\u003edata allocation\n so it is never set when oa-\u003edata is NULL.\n - Reset oa-\u003ecount to 0 at free_oa: so count and data stay\n coherent and the caller sees an empty option array.\n - Call free_svc_cred(creds) before kfree(creds) at free_creds:\n so the refcounted cr_group_info is released. free_svc_cred()\n either NULL-guards each field explicitly (cr_group_info has\n an if() check) or delegates to a helper that is NULL-safe\n itself (kfree for the string fields, gss_mech_put() which\n guards with if(gm) at gss_mech_switch.c:342), so it is safe\n to call on a partially decoded svc_cred where only\n cr_uid/cr_gid/cr_group_info have been written and everything\n else is zero from kzalloc.\n - In gssx_dec_linux_creds()\u0027s out_free_groups: path, release\n cr_group_info with put_group_info() rather than groups_free()\n so the teardown matches free_svc_cred()\u0027s refcount-aware path,\n and clear the pointer so a later free_svc_cred() on the same\n creds does not release it a second time.",
"id": "GHSA-xwc4-2qqp-pxh3",
"modified": "2026-09-13T09:32:17Z",
"published": "2026-09-11T21:31:31Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-89544"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/3ff45361e9469e85c0f86b8e7b82c63e50bab8ef"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/5e9a94539b1ec17a89177d952badfd0d844d694a"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/f85a83774d7f4e2ac71c0c384df0dfb6f7d0179a"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
"type": "CVSS_V3"
}
]
}
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