[PATCH v2 01/10] fbcon: Avoid OOB font access if console rotation fails

Thomas Zimmermann
2026-04-07T09:26:07Z

Clear the font buffer if the reallocation during console rotation fails
in fbcon_rotate_font(). The putcs implementations for the rotated buffer
will return early in this case. See [1] for an example.

Currently, fbcon_rotate_font() keeps the old buffer, which is too small
for the rotated font. Printing to the rotated console with a high-enough
character code will overflow the font buffer.

v2:
- fix typos in commit message

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Fixes: 6cc50e1c5b57 ("[PATCH] fbcon: Console Rotation - Add support to rotate font bitmap")
Cc: <stable@vger.kernel.org> # v2.6.15+
Link: https://elixir.bootlin.com/linux/v6.19/source/drivers/video/fbdev/core/fbcon_ccw.c#L144 # [1]
---
drivers/video/fbdev/core/fbcon_rotate.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/video/fbdev/core/fbcon_rotate.c b/drivers/video/fbdev/core/fbcon_rotate.c
index 1562a8f20b4f..5348f6c6f57c 100644
--- a/drivers/video/fbdev/core/fbcon_rotate.c
+++ b/drivers/video/fbdev/core/fbcon_rotate.c
@@ -46,6 +46,10 @@ int fbcon_rotate_font(struct fb_info *info, struct vc_data *vc)
info->fbops->fb_sync(info);

if (par->fd_size < d_cellsize * len) {
+ kfree(par->fontbuffer);
+ par->fontbuffer = NULL;
+ par->fd_size = 0;
+
dst = kmalloc_array(len, d_cellsize, GFP_KERNEL);

if (dst == NULL) {
@@ -54,7 +58,6 @@ int fbcon_rotate_font(struct fb_info *info, struct vc_data *vc)
}

par->fd_size = d_cellsize * len;
- kfree(par->fontbuffer);
par->fontbuffer = dst;
}

--
2.53.0