FAILED: patch "[PATCH] tty: vt: fix memory leak in vc_allocate()" failed to apply to 5.10-stable tree

The patch below does not apply to the 5.10-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-5.10.y
git checkout FETCH_HEAD
git cherry-pick -x 5b114bfc1dfd88f9d50822d532f7f1fce0f7388a
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026100541-capacity-sliced-a54b@gregkh' --subject-prefix 'PATCH 5.10.y' 'HEAD^..'

Possible dependencies:

thanks,

greg k-h

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

From 5b114bfc1dfd88f9d50822d532f7f1fce0f7388a Mon Sep 17 00:00:00 2001
From: Mingyu Wang <[email protected]>
Date: Mon, 3 Aug 2026 22:45:56 +0800
Subject: [PATCH] tty: vt: fix memory leak in vc_allocate()

If the screen buffer allocation fails in vc_allocate(), the error handling path jumps to err_free. However, this path fails to release the unicode screen map attached to vc->uni_pagedict_loc.

During the early stages of vc_allocate(), the unicode screen map is either newly allocated via con_set_default_unimap() or shares the default unicode map from a previously initialized console (which increments its refcount). If the subsequent kzalloc() for the screen buffer fails, the err_free path frees the vc structure but leaves the attached uni_pagedict with an elevated refcount. This results in an unreferenced object memory leak, as the reference to the dictionary is lost and its refcount can never reach zero.

This issue was discovered by DevGen (an automated virtual device modeling fuzzer based on Syzkaller). During fuzzing with kernel fault injection (failslab) enabled, the fuzzer forcefully failed the kzalloc() for the screen buffer, exposing this error-handling path leak.

Fix this by checking *vc->uni_pagedict_loc and calling con_free_unimap(vc) in the err_free path before kfree(vc). This safely decrements the refcount and releases the dictionary memory if this was the last reference. The explicit check is added to maintain consistency with other callers.

index 57edf37495a8..51f8fd103dcf 100644
@@ -1134,6 +1134,8 @@ int vc_allocate(unsigned int currcons)	/* return 0 on success */
 	return 0;
 err_free:
 	visual_deinit(vc);
+	if (*vc->uni_pagedict_loc)
+		con_free_unimap(vc);
 	kfree(vc);
 	vc_cons[currcons].d = NULL;
 	return err;

From: Mingyu Wang <[email protected]>

[ Upstream commit 5b114bfc1dfd88f9d50822d532f7f1fce0f7388a ]

If the screen buffer allocation fails in vc_allocate(), the error handling path jumps to err_free. However, this path fails to release the unicode screen map attached to vc->uni_pagedict_loc.

During the early stages of vc_allocate(), the unicode screen map is either newly allocated via con_set_default_unimap() or shares the default unicode map from a previously initialized console (which increments its refcount). If the subsequent kzalloc() for the screen buffer fails, the err_free path frees the vc structure but leaves the attached uni_pagedict with an elevated refcount. This results in an unreferenced object memory leak, as the reference to the dictionary is lost and its refcount can never reach zero.

This issue was discovered by DevGen (an automated virtual device modeling fuzzer based on Syzkaller). During fuzzing with kernel fault injection (failslab) enabled, the fuzzer forcefully failed the kzalloc() for the screen buffer, exposing this error-handling path leak.

Fix this by checking *vc->uni_pagedict_loc and calling con_free_unimap(vc) in the err_free path before kfree(vc). This safely decrements the refcount and releases the dictionary memory if this was the last reference. The explicit check is added to maintain consistency with other callers.

---
 drivers/tty/vt/vt.c | 2 ++
 1 file changed, 2 insertions(+)

index 30be40d3dcffa..474f6abc900b0 100644
@@ -1161,6 +1161,8 @@ int vc_allocate(unsigned int currcons)	/* return 0 on success */
 	return 0;
 err_free:
 	visual_deinit(vc);
+	if (*vc->vc_uni_pagedir_loc)
+		con_free_unimap(vc);
 	kfree(vc);
 	vc_cons[currcons].d = NULL;
 	return err;

2.53.0