5.4-stable review patch. If anyone has any objections, please let me know.
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From: Samasth Norway Ananda samasth.norway.ananda@oracle.com
commit 1a194e6c8e1ee745e914b0b7f50fa86c89ed13fe upstream.
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 samasth.norway.ananda@oracle.com Reviewed-by: Thomas Zimmermann tzimmermann@suse.de Fixes: 39b3cffb8cf3 ("fbcon: prevent user font height or width change from causing potential out-of-bounds access") Cc: George Kennedy george.kennedy@oracle.com Cc: stable stable@vger.kernel.org Cc: syzbot+38a3699c7eaf165b97a6@syzkaller.appspotmail.com Cc: Greg Kroah-Hartman gregkh@linuxfoundation.org Cc: Simona Vetter simona@ffwll.ch Cc: Helge Deller deller@gmx.de Cc: Thomas Zimmermann tzimmermann@suse.de Cc: "Ville Syrjälä" ville.syrjala@linux.intel.com Cc: Sam Ravnborg sam@ravnborg.org Cc: Qianqiang Liu qianqiang.liu@163.com Cc: Shixiong Ou oushixiong@kylinos.cn Cc: Kees Cook kees@kernel.org Cc: stable@vger.kernel.org # v5.9+ Signed-off-by: Thomas Zimmermann tzimmermann@suse.de Link: https://lore.kernel.org/r/20250912170023.3931881-1-samasth.norway.ananda@ora... Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/video/fbdev/core/fbcon.c | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-)
--- a/drivers/video/fbdev/core/fbcon.c +++ b/drivers/video/fbdev/core/fbcon.c @@ -2509,9 +2509,16 @@ static int fbcon_set_font(struct vc_data 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;