From: Junjie Cao <junjie.cao@intel.com>
To: Simona Vetter <simona@ffwll.ch>, Helge Deller <deller@gmx.de>,
Zsolt Kajtar <soci@c64.rulez.org>
Cc: Albin Babu Varghese <albinbabuvarghese20@gmail.com>,
linux-fbdev@vger.kernel.org, dri-devel@lists.freedesktop.org,
linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com,
Junjie Cao <junjie.cao@intel.com>,
syzbot+793cf822d213be1a74f2@syzkaller.appspotmail.com
Subject: [PATCH] fbdev: bitblit: bound-check glyph index in bit_putcs*
Date: Mon, 20 Oct 2025 07:53:31 +0800 [thread overview]
Message-ID: <20251019235331.1243671-1-junjie.cao@intel.com> (raw)
bit_putcs_aligned()/unaligned() derived the glyph pointer from the
character value masked by 0xff/0x1ff, which may exceed the actual font's
glyph count and read past the end of the built-in font array.
Clamp the index to the actual glyph count before computing the address.
This fixes a global out-of-bounds read reported by syzbot.
Reported-by: syzbot+793cf822d213be1a74f2@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=793cf822d213be1a74f2
Tested-by: syzbot+793cf822d213be1a74f2@syzkaller.appspotmail.com
Signed-off-by: Junjie Cao <junjie.cao@intel.com>
---
drivers/video/fbdev/core/bitblit.c | 14 ++++++++++----
1 file changed, 10 insertions(+), 4 deletions(-)
diff --git a/drivers/video/fbdev/core/bitblit.c b/drivers/video/fbdev/core/bitblit.c
index a9ec7f488522..710883831826 100644
--- a/drivers/video/fbdev/core/bitblit.c
+++ b/drivers/video/fbdev/core/bitblit.c
@@ -79,12 +79,15 @@ static inline void bit_putcs_aligned(struct vc_data *vc, struct fb_info *info,
struct fb_image *image, u8 *buf, u8 *dst)
{
u16 charmask = vc->vc_hi_font_mask ? 0x1ff : 0xff;
+ unsigned int charcnt = vc->vc_font.charcount;
u32 idx = vc->vc_font.width >> 3;
u8 *src;
while (cnt--) {
- src = vc->vc_font.data + (scr_readw(s++)&
- charmask)*cellsize;
+ u16 ch = scr_readw(s++) & charmask;
+ if (ch >= charcnt)
+ ch = 0;
+ src = vc->vc_font.data + (unsigned int)ch * cellsize;
if (attr) {
update_attr(buf, src, attr, vc);
@@ -112,14 +115,17 @@ static inline void bit_putcs_unaligned(struct vc_data *vc,
u8 *dst)
{
u16 charmask = vc->vc_hi_font_mask ? 0x1ff : 0xff;
+ unsigned int charcnt = vc->vc_font.charcount;
u32 shift_low = 0, mod = vc->vc_font.width % 8;
u32 shift_high = 8;
u32 idx = vc->vc_font.width >> 3;
u8 *src;
while (cnt--) {
- src = vc->vc_font.data + (scr_readw(s++)&
- charmask)*cellsize;
+ u16 ch = scr_readw(s++) & charmask;
+ if (ch >= charcnt)
+ ch = 0;
+ src = vc->vc_font.data + (unsigned int)ch * cellsize;
if (attr) {
update_attr(buf, src, attr, vc);
--
2.48.1
next reply other threads:[~2025-10-19 15:54 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-10-19 23:53 Junjie Cao [this message]
2025-10-20 8:21 ` Thomas Zimmermann
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