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| author |   Murad Masimov <m.masimov@mt-integration.ru> | 2025-04-28 18:34:07 +0300 |
|---|---|---|
| committer |   Helge Deller <deller@gmx.de> | 2025-05-31 10:24:02 +0200 |
| commit | 05f6e183879d9785a3cdf2f08a498bc31b7a20aa (patch) | |
| tree | 04bf0161ec87389e2ac34b101a22db6991ee465d | |
| parent | fbdev: Fix do_register_framebuffer to prevent null-ptr-deref in fb_videomode_to_var (diff) | |
| download | wireguard-linux-05f6e183879d9785a3cdf2f08a498bc31b7a20aa.tar.xz wireguard-linux-05f6e183879d9785a3cdf2f08a498bc31b7a20aa.zip | |
fbdev: Fix fb_set_var to prevent null-ptr-deref in fb_videomode_to_var
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 failure 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>
Signed-off-by: Helge Deller <deller@gmx.de>
| -rw-r--r-- | drivers/video/fbdev/core/fbmem.c | 4 |
1 files changed, 3 insertions, 1 deletions
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; |