[Linux-kernel-mentees] [PATCH 3/3] fbcon: Fix global-out-of-bounds read in fbcon_get_font()
From: Peilin Ye <hidden>
Date: 2020-09-24 13:45:06
Also in:
dri-devel, linux-fbdev, lkml
Subsystem:
framebuffer console, framebuffer core, framebuffer layer, the rest · Maintainers:
Helge Deller, Thomas Zimmermann, Simona Vetter, Linus Torvalds
fbcon_get_font() is reading out-of-bounds. A malicious user may resize `vc->vc_font.height` to a large value, causing fbcon_get_font() to read out of `fontdata`. fbcon_get_font() handles both built-in and user-provided fonts. Fortunately, recently we have added FONT_EXTRA_WORDS support for built-in fonts, so fix it by adding range checks using FNTSIZE(). This patch depends on patch "fbdev, newport_con: Move FONT_EXTRA_WORDS macros into linux/font.h", and patch "Fonts: Support FONT_EXTRA_WORDS macros for built-in fonts". Cc: stable@vger.kernel.org Reported-and-tested-by: syzbot+29d4ed7f3bdedf2aa2fd@syzkaller.appspotmail.com Link: https://syzkaller.appspot.com/bug?id=08b8be45afea11888776f897895aef9ad1c3ecfd Signed-off-by: Peilin Ye <redacted> --- drivers/video/fbdev/core/fbcon.c | 12 ++++++++++++ 1 file changed, 12 insertions(+)
diff --git a/drivers/video/fbdev/core/fbcon.c b/drivers/video/fbdev/core/fbcon.c
index 66167830fefd..bda24c64e646 100644
--- a/drivers/video/fbdev/core/fbcon.c
+++ b/drivers/video/fbdev/core/fbcon.c@@ -2492,6 +2492,9 @@ static int fbcon_get_font(struct vc_data *vc, struct console_font *font) if (font->width <= 8) { j = vc->vc_font.height; + if (font->charcount * j > FNTSIZE(fontdata)) + return -EINVAL; + for (i = 0; i < font->charcount; i++) { memcpy(data, fontdata, j); memset(data + j, 0, 32 - j);
@@ -2500,6 +2503,9 @@ static int fbcon_get_font(struct vc_data *vc, struct console_font *font) } } else if (font->width <= 16) { j = vc->vc_font.height * 2; + if (font->charcount * j > FNTSIZE(fontdata)) + return -EINVAL; + for (i = 0; i < font->charcount; i++) { memcpy(data, fontdata, j); memset(data + j, 0, 64 - j);
@@ -2507,6 +2513,9 @@ static int fbcon_get_font(struct vc_data *vc, struct console_font *font) fontdata += j; } } else if (font->width <= 24) { + if (font->charcount * (vc->vc_font.height * sizeof(u32)) > FNTSIZE(fontdata)) + return -EINVAL; + for (i = 0; i < font->charcount; i++) { for (j = 0; j < vc->vc_font.height; j++) { *data++ = fontdata[0];
@@ -2519,6 +2528,9 @@ static int fbcon_get_font(struct vc_data *vc, struct console_font *font) } } else { j = vc->vc_font.height * 4; + if (font->charcount * j > FNTSIZE(fontdata)) + return -EINVAL; + for (i = 0; i < font->charcount; i++) { memcpy(data, fontdata, j); memset(data + j, 0, 128 - j);
--
2.25.1
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