In the Linux kernel, the following vulnerability has been resolved: SUNRPC: fix gssx_dec_option_array error path bugs Four coupled defects

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:

 1gssp_accept_sec_context_upcall()
 2  gssx_dec_accept_sec_context()
 3    gssx_dec_option_array()        /* fails, count=1 data=NULL */
 4  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.