All of lore.kernel.org
 help / color / mirror / Atom feed
From: "Jiri Slaby (SUSE)" <jirislaby@kernel.org>
To: daniel@ffwll.ch
Cc: linux-fbdev@vger.kernel.org, dri-devel@lists.freedesktop.org,
	linux-kernel@vger.kernel.org,
	"Jiri Slaby (SUSE)" <jirislaby@kernel.org>,
	Ubisectech Sirius <bugreport@ubisectech.com>,
	Helge Deller <deller@gmx.de>
Subject: [PATCH] fbcon: always restore the old font data in fbcon_do_set_font()
Date: Thu,  8 Feb 2024 12:44:11 +0100	[thread overview]
Message-ID: <20240208114411.14604-1-jirislaby@kernel.org> (raw)

Commit a5a923038d70 (fbdev: fbcon: Properly revert changes when
vc_resize() failed) started restoring old font data upon failure (of
vc_resize()). But it performs so only for user fonts. It means that the
"system"/internal fonts are not restored at all. So in result, the very
first call to fbcon_do_set_font() performs no restore at all upon
failing vc_resize().

This can be reproduced by Syzkaller to crash the system on the next
invocation of font_get(). It's rather hard to hit the allocation failure
in vc_resize() on the first font_set(), but not impossible. Esp. if
fault injection is used to aid the execution/failure. It was
demonstrated by Sirius:
  BUG: unable to handle page fault for address: fffffffffffffff8
  #PF: supervisor read access in kernel mode
  #PF: error_code(0x0000) - not-present page
  PGD cb7b067 P4D cb7b067 PUD cb7d067 PMD 0
  Oops: 0000 [#1] PREEMPT SMP KASAN
  CPU: 1 PID: 8007 Comm: poc Not tainted 6.7.0-g9d1694dc91ce #20
  Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014
  RIP: 0010:fbcon_get_font+0x229/0x800 drivers/video/fbdev/core/fbcon.c:2286
  Call Trace:
   <TASK>
   con_font_get drivers/tty/vt/vt.c:4558 [inline]
   con_font_op+0x1fc/0xf20 drivers/tty/vt/vt.c:4673
   vt_k_ioctl drivers/tty/vt/vt_ioctl.c:474 [inline]
   vt_ioctl+0x632/0x2ec0 drivers/tty/vt/vt_ioctl.c:752
   tty_ioctl+0x6f8/0x1570 drivers/tty/tty_io.c:2803
   vfs_ioctl fs/ioctl.c:51 [inline]
  ...

So restore the font data in any case, not only for user fonts. Note the
later 'if' is now protected by 'old_userfont' and not 'old_data' as the
latter is always set now. (And it is supposed to be non-NULL. Otherwise
we would see the bug above again.)

Signed-off-by: Jiri Slaby (SUSE) <jirislaby@kernel.org>
Fixes: a5a923038d70 ("fbdev: fbcon: Properly revert changes when vc_resize() failed")
Cc: Ubisectech Sirius <bugreport@ubisectech.com>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Helge Deller <deller@gmx.de>
Cc: linux-fbdev@vger.kernel.org
Cc: dri-devel@lists.freedesktop.org
---
 drivers/video/fbdev/core/fbcon.c | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/drivers/video/fbdev/core/fbcon.c b/drivers/video/fbdev/core/fbcon.c
index 17a9fc80b4e4..98d0e2dbcd2f 100644
--- a/drivers/video/fbdev/core/fbcon.c
+++ b/drivers/video/fbdev/core/fbcon.c
@@ -2395,11 +2395,9 @@ static int fbcon_do_set_font(struct vc_data *vc, int w, int h, int charcount,
 	struct fbcon_ops *ops = info->fbcon_par;
 	struct fbcon_display *p = &fb_display[vc->vc_num];
 	int resize, ret, old_userfont, old_width, old_height, old_charcount;
-	char *old_data = NULL;
+	u8 *old_data = vc->vc_font.data;
 
 	resize = (w != vc->vc_font.width) || (h != vc->vc_font.height);
-	if (p->userfont)
-		old_data = vc->vc_font.data;
 	vc->vc_font.data = (void *)(p->fontdata = data);
 	old_userfont = p->userfont;
 	if ((p->userfont = userfont))
@@ -2433,13 +2431,13 @@ static int fbcon_do_set_font(struct vc_data *vc, int w, int h, int charcount,
 		update_screen(vc);
 	}
 
-	if (old_data && (--REFCOUNT(old_data) == 0))
+	if (old_userfont && (--REFCOUNT(old_data) == 0))
 		kfree(old_data - FONT_EXTRA_WORDS * sizeof(int));
 	return 0;
 
 err_out:
 	p->fontdata = old_data;
-	vc->vc_font.data = (void *)old_data;
+	vc->vc_font.data = old_data;
 
 	if (userfont) {
 		p->userfont = old_userfont;
-- 
2.43.0


             reply	other threads:[~2024-02-08 11:44 UTC|newest]

Thread overview: 2+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2024-02-08 11:44 Jiri Slaby (SUSE) [this message]
2024-02-26 15:51 ` [PATCH] fbcon: always restore the old font data in fbcon_do_set_font() Daniel Vetter

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20240208114411.14604-1-jirislaby@kernel.org \
    --to=jirislaby@kernel.org \
    --cc=bugreport@ubisectech.com \
    --cc=daniel@ffwll.ch \
    --cc=deller@gmx.de \
    --cc=dri-devel@lists.freedesktop.org \
    --cc=linux-fbdev@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.