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Thu, 25 Sep 2025 14:47:38 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id JTSDBgpW1WiORwAAD6G6ig (envelope-from ); Thu, 25 Sep 2025 14:47:38 +0000 Message-ID: <1247a6b2-b850-4a73-9df2-981ea23b5af4@suse.de> Date: Thu, 25 Sep 2025 16:47:37 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH] tty: vt: Fix vc_origin buffer copy overflow in fbcon_prepare_logo() From: Thomas Zimmermann To: Wang ShaoBo , deller@gmx.de Cc: leijitang@huawei.com, qianqiang.liu@163.com, daniel.vetter@ffwll.ch, linux-kernel@vger.kernel.org, xiexiuqi@huawei.com, dri-devel , Linux Fbdev development list References: <20250925091525.767477-1-bobo.shaobowang@huawei.com> Content-Language: en-US Autocrypt: addr=tzimmermann@suse.de; keydata= xsBNBFs50uABCADEHPidWt974CaxBVbrIBwqcq/WURinJ3+2WlIrKWspiP83vfZKaXhFYsdg XH47fDVbPPj+d6tQrw5lPQCyqjwrCPYnq3WlIBnGPJ4/jreTL6V+qfKRDlGLWFjZcsrPJGE0 BeB5BbqP5erN1qylK9i3gPoQjXGhpBpQYwRrEyQyjuvk+Ev0K1Jc5tVDeJAuau3TGNgah4Yc hdHm3bkPjz9EErV85RwvImQ1dptvx6s7xzwXTgGAsaYZsL8WCwDaTuqFa1d1jjlaxg6+tZsB 9GluwvIhSezPgnEmimZDkGnZRRSFiGP8yjqTjjWuf0bSj5rUnTGiyLyRZRNGcXmu6hjlABEB AAHNJ1Rob21hcyBaaW1tZXJtYW5uIDx0emltbWVybWFubkBzdXNlLmRlPsLAjgQTAQgAOAIb AwULCQgHAgYVCgkICwIEFgIDAQIeAQIXgBYhBHIX+6yM6c9jRKFo5WgNwR1TC3ojBQJftODH AAoJEGgNwR1TC3ojx1wH/0hKGWugiqDgLNXLRD/4TfHBEKmxIrmfu9Z5t7vwUKfwhFL6hqvo lXPJJKQpQ2z8+X2vZm/slsLn7J1yjrOsoJhKABDi+3QWWSGkaGwRJAdPVVyJMfJRNNNIKwVb U6B1BkX2XDKDGffF4TxlOpSQzdtNI/9gleOoUA8+jy8knnDYzjBNOZqLG2FuTdicBXblz0Mf vg41gd9kCwYXDnD91rJU8tzylXv03E75NCaTxTM+FBXPmsAVYQ4GYhhgFt8S2UWMoaaABLDe 7l5FdnLdDEcbmd8uLU2CaG4W2cLrUaI4jz2XbkcPQkqTQ3EB67hYkjiEE6Zy3ggOitiQGcqp j//OwE0EWznS4AEIAMYmP4M/V+T5RY5at/g7rUdNsLhWv1APYrh9RQefODYHrNRHUE9eosYb T6XMryR9hT8XlGOYRwKWwiQBoWSDiTMo/Xi29jUnn4BXfI2px2DTXwc22LKtLAgTRjP+qbU6 3Y0xnQN29UGDbYgyyK51DW3H0If2a3JNsheAAK+Xc9baj0LGIc8T9uiEWHBnCH+RdhgATnWW GKdDegUR5BkDfDg5O/FISymJBHx2Dyoklv5g4BzkgqTqwmaYzsl8UxZKvbaxq0zbehDda8lv hFXodNFMAgTLJlLuDYOGLK2AwbrS3Sp0AEbkpdJBb44qVlGm5bApZouHeJ/+n+7r12+lqdsA EQEAAcLAdgQYAQgAIAIbDBYhBHIX+6yM6c9jRKFo5WgNwR1TC3ojBQJftOH6AAoJEGgNwR1T C3ojVSkIALpAPkIJPQoURPb1VWjh34l0HlglmYHvZszJWTXYwavHR8+k6Baa6H7ufXNQtThR yIxJrQLW6rV5lm7TjhffEhxVCn37+cg0zZ3j7zIsSS0rx/aMwi6VhFJA5hfn3T0TtrijKP4A SAQO9xD1Zk9/61JWk8OysuIh7MXkl0fxbRKWE93XeQBhIJHQfnc+YBLprdnxR446Sh8Wn/2D Ya8cavuWf2zrB6cZurs048xe0UbSW5AOSo4V9M0jzYI4nZqTmPxYyXbm30Kvmz0rYVRaitYJ 4kyYYMhuULvrJDMjZRvaNe52tkKAvMevcGdt38H4KSVXAylqyQOW5zvPc4/sq9c= In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Spamd-Result: default: False [-4.30 / 50.00]; BAYES_HAM(-3.00)[100.00%]; NEURAL_HAM_LONG(-1.00)[-1.000]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; ARC_NA(0.00)[]; TO_DN_SOME(0.00)[]; FREEMAIL_TO(0.00)[huawei.com,gmx.de]; RCVD_VIA_SMTP_AUTH(0.00)[]; FUZZY_RATELIMITED(0.00)[rspamd.com]; MIME_TRACE(0.00)[0:+]; RCVD_TLS_ALL(0.00)[]; RCPT_COUNT_SEVEN(0.00)[9]; FREEMAIL_ENVRCPT(0.00)[163.com,gmx.de]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; FROM_HAS_DN(0.00)[]; FREEMAIL_CC(0.00)[huawei.com,163.com,ffwll.ch,vger.kernel.org,lists.freedesktop.org]; MID_RHS_MATCH_FROM(0.00)[]; FROM_EQ_ENVFROM(0.00)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; URIBL_BLOCKED(0.00)[huawei.com:email,qemu.org:url,suse.de:mid,suse.de:email,imap1.dmz-prg2.suse.org:helo]; DBL_BLOCKED_OPENRESOLVER(0.00)[suse.de:mid,suse.de:email,huawei.com:email] X-Spam-Flag: NO X-Spam-Level: X-Spam-Score: -4.30 Am 25.09.25 um 16:24 schrieb Thomas Zimmermann: > Hi > > Am 25.09.25 um 11:15 schrieb Wang ShaoBo: >> I got some KASAN report as below: >> >> BUG: KASAN: slab-use-after-free in fbcon_prepare_logo+0x61e/0xc90 >> Read of size 14 at addr ffff88812c9a4c38 by task syz.0.3549/19016 >> >> CPU: 0 PID: 19016 Comm: syz.0.3549 Not tainted 6.6.0+ #80 >> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), >> BIOS rel-1.14.0-0-g155821a1990b-prebuilt.qemu.org 04/01/2014 >> Call Trace: >>   >>   dump_stack_lvl+0x72/0xa0 >>   print_address_description.constprop.0+0x6b/0x3d0 >>   ? fbcon_prepare_logo+0x61e/0xc90 >>   print_report+0xba/0x280 >>   ? fbcon_prepare_logo+0x61e/0xc90 >>   ? kasan_addr_to_slab+0xd/0xa0 >>   ? fbcon_prepare_logo+0x61e/0xc90 >>   kasan_report+0xaf/0xe0 >>   ? fbcon_prepare_logo+0x61e/0xc90 >>   kasan_check_range+0x100/0x1c0 >>   __asan_memcpy+0x23/0x60 >>   fbcon_prepare_logo+0x61e/0xc90 >>   fbcon_init+0xeb9/0x1db0 >>   ? __pfx_drm_fb_helper_set_par+0x10/0x10 >>   visual_init+0x310/0x5c0 >>   do_bind_con_driver.isra.0+0x627/0xbd0 >>   store_bind+0x60b/0x710 >>   ? __pfx_store_bind+0x10/0x10 >>   dev_attr_store+0x5a/0x90 >>   ? __pfx_dev_attr_store+0x10/0x10 >>   sysfs_kf_write+0x145/0x1b0 >>   kernfs_fop_write_iter+0x367/0x580 >>   ? __pfx_sysfs_kf_write+0x10/0x10 >>   new_sync_write+0x1b1/0x2d0 >>   ? __pfx_new_sync_write+0x10/0x10 >>   ? rb_commit+0x121/0x910 >>   ? avc_policy_seqno+0xe/0x20 >>   ? selinux_file_permission+0x129/0x5d0 >>   ? security_file_permission+0xa8/0x700 >>   vfs_write+0x71a/0x960 >>   ksys_write+0x12e/0x260 >> >> fbcon_init() >>     -> vc_resize() >>     //success resize vc_origin buffer size=224=7(cols)*2*16(rows) >>     -> bcon_prepare_logo(vc, info, old_cols, old_rows, >>                              new_cols, new_rows) >>     //old_cols=256，old_rows=4，new_cols=7，new_rows=16 >> >> There happened to be a vc_origin buffer copy overflow error in >> fbcon_prepare_logo(), scrolling screen down when using old cols >> after vc resize would trigger out of lower bound of vc_origin buffer. >> >> Fixes: 6104c37094e7 ("fbcon: Make fbcon a built-time depency for fbdev") > > That's probably not the broken commit. According to 'git blame', the > broken code dates back to the initial git import. During the pre-git > days, the change at [1] might be have introduced he issue. > > Maybe drop the Fixes tag entirely. > > [1] > https://git.kernel.org/pub/scm/linux/kernel/git/tglx/history.git/commit/?id=458a55138545b8b098feb29aaf2e509f8fbab4b3 > >> Signed-off-by: Wang ShaoBo > > This looks like a sensible change to me, although I can't claim to > fully understand what the function does. > > Acked-by: Thomas Zimmermann > > Best regards > Thomas > >> --- >>   drivers/video/fbdev/core/fbcon.c | 2 ++ >>   1 file changed, 2 insertions(+) >> >> diff --git a/drivers/video/fbdev/core/fbcon.c >> b/drivers/video/fbdev/core/fbcon.c >> index ac3c99ed92d1..6fa81d0297a0 100644 >> --- a/drivers/video/fbdev/core/fbcon.c >> +++ b/drivers/video/fbdev/core/fbcon.c >> @@ -610,6 +610,8 @@ static void fbcon_prepare_logo(struct vc_data >> *vc, struct fb_info *info, >>           /* We can scroll screen down */ >>           r = q - step - cols; >>           for (cnt = rows - logo_lines; cnt > 0; cnt--) { >> +            if (r < (unsigned short *) vc->vc_origin) >> +                break; >>               scr_memcpyw(r + step, r, vc->vc_size_row); >>               r -= cols; >>           } > -- -- Thomas Zimmermann Graphics Driver Developer SUSE Software Solutions Germany GmbH Frankenstrasse 146, 90461 Nuernberg, Germany GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman HRB 36809 (AG Nuernberg)