From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 90CF1322533 for ; Sun, 5 Jul 2026 14:09:01 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783260542; cv=none; b=SkuGFlFLsgq5w838vICxK6vcGCetWw6IyCGn732fAFeeEDqQ6fiLwrHQf1aO9xNTvVPc+joWJ0kKlNwK0BeBLE7Eq5aWPmeIdPhvg97IkDUIIZLKNG+djgjTWKHUvq0dUfcNIJ0GK4Vbmy9/VI37b7eiXl+CkzD0IRGMEj78CTg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783260542; c=relaxed/simple; bh=YJ9rMJS83Otub89LJmGlk2kuDnhSRgS6EuMBFO1p6+o=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=sDuGevr+TEn+7+HkJ4bXIFMeLVrI+iWIcKQFEoWjO01JuoMVyNMLpcp+JEPRSkKO+oV6WLFrqu2bhgJwtozYEIUh0F/9Ua2rMzFVxBYjMMzuJTRYBAKfotu98a7LTS0KYNLtCuK8J6aJoshIWDV67aX5mdNyZ2I0+wdILUM/Gt4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=LSsMBwV+; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="LSsMBwV+" Received: by smtp.kernel.org (Postfix) with ESMTPSA id DFBE11F000E9; Sun, 5 Jul 2026 14:09:00 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1783260541; bh=4Bn7Y5aHbrqyeO7mol6I1uSHiOaF1VZu6eHdxzoAUsA=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=LSsMBwV+OGRCLwBawiUnXH+Z5DuLMcj/PXfiKvx81XOV5MjXBuwDxSC/V96rZmojh pO2itbpRRSNgE5O1tQ841jOUQajytpkLsCrd38TuZUvhyyVrM7enVWT/v16m9poX16 B2F7HFzwBV94H1Pf9j7Eqz7ba7O11qd4BBx2X6axN6mtD2VP/pYrgZe3TeaHcGRuqh xOo68ebW2gXIS/Gh4+uPRsQY6uTd55q/D+pX+MH4Ra+oDlbhZ12kYczahOtbCrOSry PmlaYi/W9+lzUTo+Bn/uYACpXd5iDDrI3Me4GbJ5bAfC1GLJzNd4v+JS93QWod99N3 YE7+k1E1HAN4g== From: Sasha Levin To: stable@vger.kernel.org Cc: Mingyu Wang <25181214217@stu.xidian.edu.cn>, Thomas Zimmermann , Helge Deller , Sasha Levin Subject: [PATCH 5.15.y] fbdev: fbcon: fix out-of-bounds read in err_out of fbcon_do_set_font() Date: Sun, 5 Jul 2026 10:08:59 -0400 Message-ID: <20260705140859.1776330-1-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <2026070230-congrats-plenty-c9d5@gregkh> References: <2026070230-congrats-plenty-c9d5@gregkh> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Mingyu Wang <25181214217@stu.xidian.edu.cn> [ Upstream commit 8fdc8c2057eea08d40ce2c8eed41ff9e451c65c2 ] When fbcon_do_set_font() fails (e.g., due to a memory allocation failure inside vc_resize() under heavy memory pressure), it jumps to the `err_out` label to roll back the console state. However, the current rollback logic forgets to restore the `hi_font` state, leading to a severe state machine corruption. Earlier in the function, `set_vc_hi_font()` might be called to change `vc->vc_hi_font_mask` and mutate the screen buffer. If `vc_resize()` subsequently fails, the `err_out` path restores `vc_font.charcount` but entirely skips rolling back the `vc_hi_font_mask` and the screen buffer. This mismatch leaves the terminal in a desynchronized state. Because `vc_hi_font_mask` remains set, the VT subsystem will still accept character indices greater than 255 from userspace and write them to the screen buffer. Subsequent rendering calls (e.g., `fbcon_putcs()`) will then use these inflated indices to access the reverted, 256-character font array, leading to a deterministic out-of-bounds read and potential kernel memory disclosure. Fix this by adding the missing rollback logic for the `hi_font` mask and screen buffer in the error path. Fixes: a5a923038d70 ("fbdev: fbcon: Properly revert changes when vc_resize() failed") Cc: stable@vger.kernel.org Signed-off-by: Mingyu Wang <25181214217@stu.xidian.edu.cn> Reviewed-by: Thomas Zimmermann Signed-off-by: Helge Deller [ Adjust context ] Signed-off-by: Sasha Levin --- drivers/video/fbdev/core/fbcon.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/drivers/video/fbdev/core/fbcon.c b/drivers/video/fbdev/core/fbcon.c index 7dce023c2fb34c..a3993925d8ef77 100644 --- a/drivers/video/fbdev/core/fbcon.c +++ b/drivers/video/fbdev/core/fbcon.c @@ -2381,6 +2381,7 @@ static int fbcon_do_set_font(struct vc_data *vc, int w, int h, int charcount, struct fbcon_display *p = &fb_display[vc->vc_num]; int resize, ret, old_userfont, old_width, old_height, old_charcount; u8 *old_data = vc->vc_font.data; + unsigned short old_hi_font_mask = vc->vc_hi_font_mask; resize = (w != vc->vc_font.width) || (h != vc->vc_font.height); vc->vc_font.data = (void *)(p->fontdata = data); @@ -2434,6 +2435,12 @@ static int fbcon_do_set_font(struct vc_data *vc, int w, int h, int charcount, vc->vc_font.height = old_height; vc->vc_font.charcount = old_charcount; + /* Restore the hi_font state and screen buffer */ + if (old_hi_font_mask && !vc->vc_hi_font_mask) + set_vc_hi_font(vc, true); + else if (!old_hi_font_mask && vc->vc_hi_font_mask) + set_vc_hi_font(vc, false); + return ret; } -- 2.53.0