* [PATCH 1/2] fbdev: Fix do_register_framebuffer to prevent null-ptr-deref in fb_videomode_to_var
2025-04-28 15:34 [PATCH 0/2] fbdev: Prevent null-ptr-deref in fb_videomode_to_var Murad Masimov
@ 2025-04-28 15:34 ` Murad Masimov
2025-04-28 15:34 ` [PATCH 2/2] fbdev: Fix fb_ser_var " Murad Masimov
2025-05-29 8:19 ` [PATCH 0/2] fbdev: Prevent " Helge Deller
2 siblings, 0 replies; 4+ messages in thread
From: Murad Masimov @ 2025-04-28 15:34 UTC (permalink / raw)
To: Simona Vetter
Cc: Helge Deller, Murad Masimov, Thomas Weißschuh, linux-fbdev,
dri-devel, linux-kernel, lvc-project, stable
If fb_add_videomode() in do_register_framebuffer() fails to allocate
memory for fb_videomode, it will later lead to a null-ptr dereference in
fb_videomode_to_var(), as the fb_info is registered while not having the
mode in modelist that is expected to be there, i.e. the one that is
described in fb_info->var.
================================================================
general protection fault, probably for non-canonical address 0xdffffc0000000001: 0000 [#1] PREEMPT SMP KASAN NOPTI
KASAN: null-ptr-deref in range [0x0000000000000008-0x000000000000000f]
CPU: 1 PID: 30371 Comm: syz-executor.1 Not tainted 5.10.226-syzkaller #0
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.12.0-1 04/01/2014
RIP: 0010:fb_videomode_to_var+0x24/0x610 drivers/video/fbdev/core/modedb.c:901
Call Trace:
display_to_var+0x3a/0x7c0 drivers/video/fbdev/core/fbcon.c:929
fbcon_resize+0x3e2/0x8f0 drivers/video/fbdev/core/fbcon.c:2071
resize_screen drivers/tty/vt/vt.c:1176 [inline]
vc_do_resize+0x53a/0x1170 drivers/tty/vt/vt.c:1263
fbcon_modechanged+0x3ac/0x6e0 drivers/video/fbdev/core/fbcon.c:2720
fbcon_update_vcs+0x43/0x60 drivers/video/fbdev/core/fbcon.c:2776
do_fb_ioctl+0x6d2/0x740 drivers/video/fbdev/core/fbmem.c:1128
fb_ioctl+0xe7/0x150 drivers/video/fbdev/core/fbmem.c:1203
vfs_ioctl fs/ioctl.c:48 [inline]
__do_sys_ioctl fs/ioctl.c:753 [inline]
__se_sys_ioctl fs/ioctl.c:739 [inline]
__x64_sys_ioctl+0x19a/0x210 fs/ioctl.c:739
do_syscall_64+0x33/0x40 arch/x86/entry/common.c:46
entry_SYSCALL_64_after_hwframe+0x67/0xd1
================================================================
Even though fbcon_init() checks beforehand if fb_match_mode() in
var_to_display() fails, it can not prevent the panic because fbcon_init()
does not return error code. Considering this and the comment in the code
about fb_match_mode() returning NULL - "This should not happen" - it is
better to prevent registering the fb_info if its mode was not set
successfully. Also move fb_add_videomode() closer to the beginning of
do_register_framebuffer() to avoid having to do the cleanup on fail.
Found by Linux Verification Center (linuxtesting.org) with Syzkaller.
Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Cc: stable@vger.kernel.org
Signed-off-by: Murad Masimov <m.masimov@mt-integration.ru>
---
drivers/video/fbdev/core/fbmem.c | 18 +++++++++++-------
1 file changed, 11 insertions(+), 7 deletions(-)
diff --git a/drivers/video/fbdev/core/fbmem.c b/drivers/video/fbdev/core/fbmem.c
index 3c568cff2913..e1557d80768f 100644
--- a/drivers/video/fbdev/core/fbmem.c
+++ b/drivers/video/fbdev/core/fbmem.c
@@ -388,7 +388,7 @@ static int fb_check_foreignness(struct fb_info *fi)
static int do_register_framebuffer(struct fb_info *fb_info)
{
- int i;
+ int i, err = 0;
struct fb_videomode mode;
if (fb_check_foreignness(fb_info))
@@ -397,10 +397,18 @@ static int do_register_framebuffer(struct fb_info *fb_info)
if (num_registered_fb == FB_MAX)
return -ENXIO;
- num_registered_fb++;
for (i = 0 ; i < FB_MAX; i++)
if (!registered_fb[i])
break;
+
+ if (!fb_info->modelist.prev || !fb_info->modelist.next)
+ INIT_LIST_HEAD(&fb_info->modelist);
+
+ fb_var_to_videomode(&mode, &fb_info->var);
+ err = fb_add_videomode(&mode, &fb_info->modelist);
+ if (err < 0)
+ return err;
+
fb_info->node = i;
refcount_set(&fb_info->count, 1);
mutex_init(&fb_info->lock);
@@ -426,16 +434,12 @@ static int do_register_framebuffer(struct fb_info *fb_info)
if (bitmap_empty(fb_info->pixmap.blit_y, FB_MAX_BLIT_HEIGHT))
bitmap_fill(fb_info->pixmap.blit_y, FB_MAX_BLIT_HEIGHT);
- if (!fb_info->modelist.prev || !fb_info->modelist.next)
- INIT_LIST_HEAD(&fb_info->modelist);
-
if (fb_info->skip_vt_switch)
pm_vt_switch_required(fb_info->device, false);
else
pm_vt_switch_required(fb_info->device, true);
- fb_var_to_videomode(&mode, &fb_info->var);
- fb_add_videomode(&mode, &fb_info->modelist);
+ num_registered_fb++;
registered_fb[i] = fb_info;
#ifdef CONFIG_GUMSTIX_AM200EPD
--
2.39.2
^ permalink raw reply related [flat|nested] 4+ messages in thread* [PATCH 2/2] fbdev: Fix fb_ser_var to prevent null-ptr-deref in fb_videomode_to_var
2025-04-28 15:34 [PATCH 0/2] fbdev: Prevent null-ptr-deref in fb_videomode_to_var Murad Masimov
2025-04-28 15:34 ` [PATCH 1/2] fbdev: Fix do_register_framebuffer to prevent " Murad Masimov
@ 2025-04-28 15:34 ` Murad Masimov
2025-05-29 8:19 ` [PATCH 0/2] fbdev: Prevent " Helge Deller
2 siblings, 0 replies; 4+ messages in thread
From: Murad Masimov @ 2025-04-28 15:34 UTC (permalink / raw)
To: Simona Vetter
Cc: Helge Deller, Murad Masimov, Thomas Weißschuh, linux-fbdev,
dri-devel, linux-kernel, lvc-project, stable
If fb_add_videomode() in fb_set_var() fails to allocate memory for
fb_videomode, later it may lead to a null-ptr dereference in
fb_videomode_to_var(), as the fb_info is registered while not having the
mode in modelist that is expected to be there, i.e. the one that is
described in fb_info->var.
================================================================
general protection fault, probably for non-canonical address 0xdffffc0000000001: 0000 [#1] PREEMPT SMP KASAN NOPTI
KASAN: null-ptr-deref in range [0x0000000000000008-0x000000000000000f]
CPU: 1 PID: 30371 Comm: syz-executor.1 Not tainted 5.10.226-syzkaller #0
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.12.0-1 04/01/2014
RIP: 0010:fb_videomode_to_var+0x24/0x610 drivers/video/fbdev/core/modedb.c:901
Call Trace:
display_to_var+0x3a/0x7c0 drivers/video/fbdev/core/fbcon.c:929
fbcon_resize+0x3e2/0x8f0 drivers/video/fbdev/core/fbcon.c:2071
resize_screen drivers/tty/vt/vt.c:1176 [inline]
vc_do_resize+0x53a/0x1170 drivers/tty/vt/vt.c:1263
fbcon_modechanged+0x3ac/0x6e0 drivers/video/fbdev/core/fbcon.c:2720
fbcon_update_vcs+0x43/0x60 drivers/video/fbdev/core/fbcon.c:2776
do_fb_ioctl+0x6d2/0x740 drivers/video/fbdev/core/fbmem.c:1128
fb_ioctl+0xe7/0x150 drivers/video/fbdev/core/fbmem.c:1203
vfs_ioctl fs/ioctl.c:48 [inline]
__do_sys_ioctl fs/ioctl.c:753 [inline]
__se_sys_ioctl fs/ioctl.c:739 [inline]
__x64_sys_ioctl+0x19a/0x210 fs/ioctl.c:739
do_syscall_64+0x33/0x40 arch/x86/entry/common.c:46
entry_SYSCALL_64_after_hwframe+0x67/0xd1
================================================================
The reason is that fb_info->var is being modified in fb_set_var(), and
then fb_videomode_to_var() is called. If it fails to add the mode to
fb_info->modelist, fb_set_var() returns error, but does not restore the
old value of fb_info->var. Restore fb_info->var on fail the same way it
is done earlier in the function.
Found by Linux Verification Center (linuxtesting.org) with Syzkaller.
Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Cc: stable@vger.kernel.org
Signed-off-by: Murad Masimov <m.masimov@mt-integration.ru>
---
drivers/video/fbdev/core/fbmem.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/drivers/video/fbdev/core/fbmem.c b/drivers/video/fbdev/core/fbmem.c
index e1557d80768f..eca2498f2436 100644
--- a/drivers/video/fbdev/core/fbmem.c
+++ b/drivers/video/fbdev/core/fbmem.c
@@ -328,8 +328,10 @@ fb_set_var(struct fb_info *info, struct fb_var_screeninfo *var)
!list_empty(&info->modelist))
ret = fb_add_videomode(&mode, &info->modelist);
- if (ret)
+ if (ret) {
+ info->var = old_var;
return ret;
+ }
event.info = info;
event.data = &mode;
--
2.39.2
^ permalink raw reply related [flat|nested] 4+ messages in thread