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Mon, 28 Apr 2025 18:34:56 +0300 From: Murad Masimov To: Simona Vetter CC: Helge Deller , Murad Masimov , =?utf-8?q?Thomas_Wei=C3=9Fschuh?= , , , , , Subject: [PATCH 2/2] fbdev: Fix fb_ser_var to prevent null-ptr-deref in fb_videomode_to_var Date: Mon, 28 Apr 2025 18:34:07 +0300 Message-ID: <20250428153407.3743416-3-m.masimov@mt-integration.ru> X-Mailer: git-send-email 2.39.2 In-Reply-To: <20250428153407.3743416-1-m.masimov@mt-integration.ru> References: <20250428153407.3743416-1-m.masimov@mt-integration.ru> Precedence: bulk X-Mailing-List: linux-fbdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-ClientProxiedBy: mmail-p-exch01.mt.ru (81.200.124.61) To mmail-p-exch02.mt.ru (81.200.124.62) X-KSMG-AntiPhishing: NotDetected X-KSMG-AntiSpam-Auth: dmarc=none header.from=mt-integration.ru;spf=none smtp.mailfrom=mt-integration.ru;dkim=none X-KSMG-AntiSpam-Envelope-From: m.masimov@mt-integration.ru X-KSMG-AntiSpam-Info: LuaCore: 56 0.3.56 52db7f275cc9b6820389ba9ab2ac225370e1c244, {rep_avail}, {Tracking_from_domain_doesnt_match_to}, 127.0.0.199:7.1.2; mt-integration.ru:7.1.1; 81.200.124.62:7.1.2; ksmg02.maxima.ru:7.1.1; d41d8cd98f00b204e9800998ecf8427e.com:7.1.1, FromAlignment: s, ApMailHostAddress: 81.200.124.62 X-KSMG-AntiSpam-Interceptor-Info: scan successful X-KSMG-AntiSpam-Lua-Profiles: 192977 [Apr 28 2025] X-KSMG-AntiSpam-Method: none X-KSMG-AntiSpam-Rate: 0 X-KSMG-AntiSpam-Status: not_detected X-KSMG-AntiSpam-Version: 6.1.1.11 X-KSMG-AntiVirus: Kaspersky Secure Mail Gateway, version 2.1.1.8310, bases: 2025/04/28 14:14:00 #27936619 X-KSMG-AntiVirus-Status: NotDetected, skipped X-KSMG-LinksScanning: NotDetected X-KSMG-Message-Action: skipped X-KSMG-Rule-ID: 7 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 --- drivers/video/fbdev/core/fbmem.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) -- 2.39.2 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;