From 1a194e6c8e1ee745e914b0b7f50fa86c89ed13fe Mon Sep 17 00:00:00 2001 From: Samasth Norway Ananda Date: Fri, 12 Sep 2025 10:00:23 -0700 Subject: [PATCH] fbcon: fix integer overflow in fbcon_do_set_font MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit Fix integer overflow vulnerabilities in fbcon_do_set_font() where font size calculations could overflow when handling user-controlled font parameters. The vulnerabilities occur when: 1. CALC_FONTSZ(h, pitch, charcount) performs h * pith * charcount multiplication with user-controlled values that can overflow. 2. FONT_EXTRA_WORDS * sizeof(int) + size addition can also overflow 3. This results in smaller allocations than expected, leading to buffer overflows during font data copying. Add explicit overflow checking using check_mul_overflow() and check_add_overflow() kernel helpers to safety validate all size calculations before allocation. Signed-off-by: Samasth Norway Ananda Reviewed-by: Thomas Zimmermann Fixes: 39b3cffb8cf3 ("fbcon: prevent user font height or width change from causing potential out-of-bounds access") Cc: George Kennedy Cc: stable Cc: syzbot+38a3699c7eaf165b97a6@syzkaller.appspotmail.com Cc: Greg Kroah-Hartman Cc: Simona Vetter Cc: Helge Deller Cc: Thomas Zimmermann Cc: "Ville Syrjälä" Cc: Sam Ravnborg Cc: Qianqiang Liu Cc: Shixiong Ou Cc: Kees Cook Cc: # v5.9+ Signed-off-by: Thomas Zimmermann Link: https://lore.kernel.org/r/20250912170023.3931881-1-samasth.norway.ananda@oracle.com --- drivers/video/fbdev/core/fbcon.c | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-) diff --git a/drivers/video/fbdev/core/fbcon.c b/drivers/video/fbdev/core/fbcon.c index 55f5731e94c3..a507d05f8fea 100644 --- a/drivers/video/fbdev/core/fbcon.c +++ b/drivers/video/fbdev/core/fbcon.c @@ -2531,9 +2531,16 @@ static int fbcon_set_font(struct vc_data *vc, const struct console_font *font, if (fbcon_invalid_charcount(info, charcount)) return -EINVAL; - size = CALC_FONTSZ(h, pitch, charcount); + /* Check for integer overflow in font size calculation */ + if (check_mul_overflow(h, pitch, &size) || + check_mul_overflow(size, charcount, &size)) + return -EINVAL; + + /* Check for overflow in allocation size calculation */ + if (check_add_overflow(FONT_EXTRA_WORDS * sizeof(int), size, &size)) + return -EINVAL; - new_data = kmalloc(FONT_EXTRA_WORDS * sizeof(int) + size, GFP_USER); + new_data = kmalloc(size, GFP_USER); if (!new_data) return -ENOMEM; -- 2.51.0