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