FAILED: patch "[PATCH] fbcon: Rebuild rotated font buffer on font change" failed to apply to 5.15-stable tree

[Sasha Levin <sashal@kernel.org>]

The patch below does not apply to the 5.15-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 <stable@vger.kernel.org>.

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-5.15.y
git checkout FETCH_HEAD
git cherry-pick -x e4b6b865d45d8dafb6c6f28c8a993a5b4431d25a
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '20261107061003-failed-5.15-e4b6b865d45d@kernel.org' --subject-prefix 'PATCH 5.15.y' 'HEAD^..'

Thanks,
Sasha

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

From e4b6b865d45d8dafb6c6f28c8a993a5b4431d25a Mon Sep 17 00:00:00 2001
From: Yao Yiqi <yaoyiqi3@huawei.com>
Date: Mon, 19 Oct 2026 17:43:30 +0800
Subject: [PATCH] fbcon: Rebuild rotated font buffer on font change

fbcon_rotate_font() caches a rotated copy of the console font in
par->rotated.buf. The buffer is sized from the font's width, height
and charcount, and is rebuilt in fbcon_init(), fbcon_switch() and
fbcon_modechanged(), but not in fbcon_do_set_font().

When the font is changed through KDFONTOP, the new geometry is
installed and vc_resize() redraws before the buffer is rebuilt. The
rotated putcs/cursor ops then index the old buffer with the new cell
size; KASAN reports a slab-out-of-bounds read in soft_cursor().

Rebuild the buffer for the visible console before the redraw, as the
other callers do: select the console's blitting state with
set_blitting_type() (which also uploads the new font's map on
tile-blitting hardware), then rebuild. Background consoles keep
their rebuild at fbcon_switch() time, as the buffer is shared per
framebuffer and must not be updated for a console that is not being
displayed.

To ensure a correct rollback when the rebuild or the following
vc_resize() fails, save the rotated font state, clear it before
rebuilding, and restore it in the error path of
fbcon_do_set_font().

Fixes: 6cc50e1c5b57 ("[PATCH] fbcon: Console Rotation - Add support to rotate font bitmap")
Cc: stable@vger.kernel.org
Signed-off-by: Yao Yiqi <yaoyiqi3@huawei.com>
Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
Signed-off-by: Helge Deller <deller@gmx.de>
---
 drivers/video/fbdev/core/fbcon.c | 46 ++++++++++++++++++++++++++++++++
 drivers/video/fbdev/core/fbcon.h | 22 ++++++++-------
 2 files changed, 59 insertions(+), 9 deletions(-)

diff --git a/drivers/video/fbdev/core/fbcon.c b/drivers/video/fbdev/core/fbcon.c
index ba689d42792d7..af587ff02e437 100644
--- a/drivers/video/fbdev/core/fbcon.c
+++ b/drivers/video/fbdev/core/fbcon.c
@@ -2391,6 +2391,10 @@ static int fbcon_do_set_font(struct vc_data *vc, int w, int h, int charcount,
 	font_data_t *old_fontdata = p->fontdata;
 	const u8 *old_data = vc->vc_font.data;
 	unsigned short old_hi_font_mask = vc->vc_hi_font_mask;
+#ifdef CONFIG_FRAMEBUFFER_CONSOLE_ROTATION
+	struct fbcon_rotated saved_rotated = { };
+	bool rotated_saved = false;
+#endif
 
 	font_data_get(data);
 
@@ -2409,6 +2413,27 @@ static int fbcon_do_set_font(struct vc_data *vc, int w, int h, int charcount,
 	else if (!vc->vc_hi_font_mask && charcount == 512)
 		set_vc_hi_font(vc, true);
 
+	/*
+	 * Select the console's blitting state and update par->rotated to
+	 * match the new font, so that the rendering below does not use a
+	 * cache that was built for the old font. Clear the cached state so
+	 * the rebuild allocates a fresh buffer; the old state is kept until
+	 * the font change can no longer fail.
+	 */
+	if (con_is_visible(vc)) {
+		set_blitting_type(vc, info);
+		if (par->bitops->rotate_font) {
+#ifdef CONFIG_FRAMEBUFFER_CONSOLE_ROTATION
+			saved_rotated = par->rotated;
+			memset(&par->rotated, 0, sizeof(par->rotated));
+			rotated_saved = true;
+#endif
+			ret = par->bitops->rotate_font(info, vc);
+			if (ret)
+				goto err_out;
+		}
+	}
+
 	if (resize) {
 		int cols, rows;
 
@@ -2425,12 +2450,26 @@ static int fbcon_do_set_font(struct vc_data *vc, int w, int h, int charcount,
 		update_screen(vc);
 	}
 
+#ifdef CONFIG_FRAMEBUFFER_CONSOLE_ROTATION
+	if (rotated_saved)
+		kfree(saved_rotated.buf);
+#endif
 	if (old_fontdata)
 		font_data_put(old_fontdata);
 
 	return 0;
 
 err_out:
+#ifdef CONFIG_FRAMEBUFFER_CONSOLE_ROTATION
+	/*
+	 * Drop the buffer built for the new font and restore the saved
+	 * state.
+	 */
+	if (rotated_saved) {
+		kfree(par->rotated.buf);
+		par->rotated = saved_rotated;
+	}
+#endif
 	p->fontdata = old_fontdata;
 	vc->vc_font.data = old_data;
 	vc->vc_font.width = old_width;
@@ -2443,6 +2482,13 @@ static int fbcon_do_set_font(struct vc_data *vc, int w, int h, int charcount,
 	else if (!old_hi_font_mask && vc->vc_hi_font_mask)
 		set_vc_hi_font(vc, false);
 
+	/*
+	 * Re-select the blitting type, which re-uploads the font map on
+	 * tile-blitting hardware.
+	 */
+	if (con_is_visible(vc))
+		set_blitting_type(vc, info);
+
 	font_data_put(data);
 
 	return ret;
diff --git a/drivers/video/fbdev/core/fbcon.h b/drivers/video/fbdev/core/fbcon.h
index 91b59b2990d29..d93a89877d043 100644
--- a/drivers/video/fbdev/core/fbcon.h
+++ b/drivers/video/fbdev/core/fbcon.h
@@ -72,6 +72,18 @@ struct fbcon_bitops {
 	int  (*rotate_font)(struct fb_info *info, struct vc_data *vc);
 };
 
+#ifdef CONFIG_FRAMEBUFFER_CONSOLE_ROTATION
+struct fbcon_rotated {
+	font_data_t *fontdata;       /* source font */
+	u8 *buf;                     /* rotated glyphs */
+	size_t bufsize;
+	int buf_rotate;              /* rotation of buf */
+	unsigned int buf_width;      /* geometry of source font */
+	unsigned int buf_height;
+	unsigned int buf_charcount;
+};
+#endif
+
 struct fbcon_par {
 	struct fb_var_screeninfo var;  /* copy of the current fb_var_screeninfo */
 	struct delayed_work cursor_work; /* Cursor timer */
@@ -88,15 +100,7 @@ struct fbcon_par {
 	int    rotate;
 	char  *cursor_data;
 #ifdef CONFIG_FRAMEBUFFER_CONSOLE_ROTATION
-	struct {
-		font_data_t *fontdata;       /* source font */
-		u8 *buf;                     /* rotated glyphs */
-		size_t bufsize;
-		int buf_rotate;              /* rotation of buf */
-		unsigned int buf_width;      /* geometry of source font */
-		unsigned int buf_height;
-		unsigned int buf_charcount;
-	} rotated;
+	struct fbcon_rotated rotated;
 #endif
 	u8    *cursor_src;
 	u32    cursor_size;
-- 
2.53.0