Hi
Am 20.10.25 um 15:47 schrieb Junjie Cao:
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: [email protected]
Closes: https://syzkaller.appspot.com/bug?extid=793cf822d213be1a74f2
Tested-by: [email protected]
Signed-off-by: Junjie Cao <[email protected]>
Reviewed-by: Thomas Zimmermann <[email protected]>
Thanks for fixing the bug.
Best regards
Thomas
---
v1:
https://lore.kernel.org/linux-fbdev/[email protected]/
v1 -> v2:
- Fix indentation and add blank line after declarations with the .pl helper
- No functional changes
drivers/video/fbdev/core/bitblit.c | 16 ++++++++++++----
1 file changed, 12 insertions(+), 4 deletions(-)
diff --git a/drivers/video/fbdev/core/bitblit.c
b/drivers/video/fbdev/core/bitblit.c
index 9d2e59796c3e..085ffb44c51a 100644
--- a/drivers/video/fbdev/core/bitblit.c
+++ b/drivers/video/fbdev/core/bitblit.c
@@ -79,12 +79,16 @@ 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 +116,18 @@ 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);
--
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstrasse 146, 90461 Nuernberg, Germany
GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman
HRB 36809 (AG Nuernberg)
