syzbot is reporting OOB read bug in vc_do_resize() [1] caused by memcpy()
based on outdated old_{rows,row_size} values, for resize_screen() can
recurse into vc_do_resize() which changes vc->vc_{cols,rows} that outdates
old_{rows,row_size} values which were saved before calling resize_screen().Daniel Vetter explained that resize_screen() should not recurse into fbcon_update_vcs() path due to FBINFO_MISC_USEREVENT being still set when calling resize_screen(). Instead of masking FBINFO_MISC_USEREVENT before calling fbcon_update_vcs(), we can remove FBINFO_MISC_USEREVENT by calling fbcon_update_vcs() only if fb_set_var() returned 0. This change assumes that it is harmless to call fbcon_update_vcs() when fb_set_var() returned 0 without reaching fb_notifier_call_chain(). [1] https://syzkaller.appspot.com/bug?id=c70c88cfd16dcf6e1d3c7f0ab8648b3144b5b25e Reported-and-tested-by: syzbot <syzbot+c37a14770d51a085a...@syzkaller.appspotmail.com> Suggested-by: Daniel Vetter <daniel.vet...@ffwll.ch> Signed-off-by: Tetsuo Handa <penguin-ker...@i-love.sakura.ne.jp> --- drivers/video/fbdev/core/fbmem.c | 8 ++------ drivers/video/fbdev/core/fbsysfs.c | 4 ++-- drivers/video/fbdev/ps3fb.c | 4 ++-- include/linux/fb.h | 2 -- 4 files changed, 6 insertions(+), 12 deletions(-) diff --git a/drivers/video/fbdev/core/fbmem.c b/drivers/video/fbdev/core/fbmem.c index 30e73ec..da7c88f 100644 --- a/drivers/video/fbdev/core/fbmem.c +++ b/drivers/video/fbdev/core/fbmem.c @@ -957,7 +957,6 @@ static int fb_check_caps(struct fb_info *info, struct fb_var_screeninfo *var, int fb_set_var(struct fb_info *info, struct fb_var_screeninfo *var) { - int flags = info->flags; int ret = 0; u32 activate; struct fb_var_screeninfo old_var; @@ -1052,9 +1051,6 @@ static int fb_check_caps(struct fb_info *info, struct fb_var_screeninfo *var, event.data = &mode; fb_notifier_call_chain(FB_EVENT_MODE_CHANGE, &event); - if (flags & FBINFO_MISC_USEREVENT) - fbcon_update_vcs(info, activate & FB_ACTIVATE_ALL); - return 0; } EXPORT_SYMBOL(fb_set_var); @@ -1105,9 +1101,9 @@ static long do_fb_ioctl(struct fb_info *info, unsigned int cmd, return -EFAULT; console_lock(); lock_fb_info(info); - info->flags |= FBINFO_MISC_USEREVENT; ret = fb_set_var(info, &var); - info->flags &= ~FBINFO_MISC_USEREVENT; + if (!ret) + fbcon_update_vcs(info, var.activate & FB_ACTIVATE_ALL); unlock_fb_info(info); console_unlock(); if (!ret && copy_to_user(argp, &var, sizeof(var))) diff --git a/drivers/video/fbdev/core/fbsysfs.c b/drivers/video/fbdev/core/fbsysfs.c index d54c88f..65dae05 100644 --- a/drivers/video/fbdev/core/fbsysfs.c +++ b/drivers/video/fbdev/core/fbsysfs.c @@ -91,9 +91,9 @@ static int activate(struct fb_info *fb_info, struct fb_var_screeninfo *var) var->activate |= FB_ACTIVATE_FORCE; console_lock(); - fb_info->flags |= FBINFO_MISC_USEREVENT; err = fb_set_var(fb_info, var); - fb_info->flags &= ~FBINFO_MISC_USEREVENT; + if (!err) + fbcon_update_vcs(fb_info, var->activate & FB_ACTIVATE_ALL); console_unlock(); if (err) return err; diff --git a/drivers/video/fbdev/ps3fb.c b/drivers/video/fbdev/ps3fb.c index 9df78fb..4b4a99f 100644 --- a/drivers/video/fbdev/ps3fb.c +++ b/drivers/video/fbdev/ps3fb.c @@ -824,12 +824,12 @@ static int ps3fb_ioctl(struct fb_info *info, unsigned int cmd, var = info->var; fb_videomode_to_var(&var, vmode); console_lock(); - info->flags |= FBINFO_MISC_USEREVENT; /* Force, in case only special bits changed */ var.activate |= FB_ACTIVATE_FORCE; par->new_mode_id = val; retval = fb_set_var(info, &var); - info->flags &= ~FBINFO_MISC_USEREVENT; + if (!retval) + fbcon_update_vcs(info, var.activate & FB_ACTIVATE_ALL); console_unlock(); } break; diff --git a/include/linux/fb.h b/include/linux/fb.h index 3b4b2f0..b11eb02 100644 --- a/include/linux/fb.h +++ b/include/linux/fb.h @@ -400,8 +400,6 @@ struct fb_tile_ops { #define FBINFO_HWACCEL_YPAN 0x2000 /* optional */ #define FBINFO_HWACCEL_YWRAP 0x4000 /* optional */ -#define FBINFO_MISC_USEREVENT 0x10000 /* event request - from userspace */ #define FBINFO_MISC_TILEBLITTING 0x20000 /* use tile blitting */ /* A driver may set this flag to indicate that it does want a set_par to be -- 1.8.3.1
