CVE-2026-89544

In 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 Software

References

• https://git.kernel.org/stable/c/3ff45361e9469e85c0f86b8e7b82c63e50bab8ef
• https://git.kernel.org/stable/c/5e9a94539b1ec17a89177d952badfd0d844d694a
• https://git.kernel.org/stable/c/f85a83774d7f4e2ac71c0c384df0dfb6f7d0179a
• https://git.kernel.org/stable/c/fb30241f7ccace372ee83017891549f23a715581