5.4-stable review patch. If anyone has any objections, please let me know.
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From: Junjie Cao junjie.cao@intel.com
commit 18c4ef4e765a798b47980555ed665d78b71aeadf upstream.
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 Reviewed-by: Thomas Zimmermann tzimmermann@suse.de Signed-off-by: Helge Deller deller@gmx.de Cc: stable@vger.kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/video/fbdev/core/bitblit.c | 16 ++++++++++++---- 1 file changed, 12 insertions(+), 4 deletions(-)
--- a/drivers/video/fbdev/core/bitblit.c +++ b/drivers/video/fbdev/core/bitblit.c @@ -80,12 +80,16 @@ static inline void bit_putcs_aligned(str 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); @@ -113,14 +117,18 @@ static inline void bit_putcs_unaligned(s 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);