FAILED: patch "[PATCH] SUNRPC: fix gssx_dec_option_array error path bugs" failed to apply to 6.1-stable tree

The patch below does not apply to the 6.1-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.1.y
git checkout FETCH_HEAD
git cherry-pick -x 5e9a94539b1ec17a89177d952badfd0d844d694a
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026090302-juncture-ecologist-47d8@gregkh' --subject-prefix 'PATCH 6.1.y' 'HEAD^..'

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 5e9a94539b1ec17a89177d952badfd0d844d694a Mon Sep 17 00:00:00 2001
From: Chris Mason <[email protected]>
Date: Thu, 28 May 2026 15:32:09 -0400
Subject: [PATCH] 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.

index fceee648d545..f2b8f919adea 100644
@@ -222,7 +222,8 @@ static int gssx_dec_linux_creds(struct xdr_stream *xdr,
 
 	return 0;
 out_free_groups:
-	groups_free(creds->cr_group_info);
+	put_group_info(creds->cr_group_info);
+	creds->cr_group_info = NULL;
 	return err;
 }
 

@@ -242,12 +243,12 @@ static int gssx_dec_option_array(struct xdr_stream *xdr,
 		return 0;
 
 	/* we recognize only 1 currently: CREDS_VALUE */
-	oa->count = 1;
-
 	oa->data = kmalloc_obj(struct gssx_option);
 	if (!oa->data)
 		return -ENOMEM;
 
+	oa->count = 1;
+
 	creds = kzalloc_obj(struct svc_cred);
 	if (!creds) {
 		err = -ENOMEM;

@@ -294,8 +295,10 @@ static int gssx_dec_option_array(struct xdr_stream *xdr,
 	return 0;
 
 free_creds:
+	free_svc_cred(creds);
 	kfree(creds);
 free_oa:
+	oa->count = 0;
 	kfree(oa->data);
 	oa->data = NULL;
 	return err;

From: Chris Mason <[email protected]>

[ Upstream commit 5e9a94539b1ec17a89177d952badfd0d844d694a ]

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.

---
 net/sunrpc/auth_gss/gss_rpc_xdr.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

index ee91f4d641e6f..ac9ae42a69762 100644
@@ -222,7 +222,8 @@ static int gssx_dec_linux_creds(struct xdr_stream *xdr,
 
 	return 0;
 out_free_groups:
-	groups_free(creds->cr_group_info);
+	put_group_info(creds->cr_group_info);
+	creds->cr_group_info = NULL;
 	return err;
 }
 

@@ -242,12 +243,12 @@ static int gssx_dec_option_array(struct xdr_stream *xdr,
 		return 0;
 
 	/* we recognize only 1 currently: CREDS_VALUE */
-	oa->count = 1;
-
 	oa->data = kmalloc(sizeof(struct gssx_option), GFP_KERNEL);
 	if (!oa->data)
 		return -ENOMEM;
 
+	oa->count = 1;
+
 	creds = kzalloc(sizeof(struct svc_cred), GFP_KERNEL);
 	if (!creds) {
 		err = -ENOMEM;

@@ -294,8 +295,10 @@ static int gssx_dec_option_array(struct xdr_stream *xdr,
 	return 0;
 
 free_creds:
+	free_svc_cred(creds);
 	kfree(creds);
 free_oa:
+	oa->count = 0;
 	kfree(oa->data);
 	oa->data = NULL;
 	return err;

2.53.0