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Fri, 23 Oct 2026 00:56:22 -0700 (PDT) Received: from spiderman.taila3fd8c.ts.net ([202.112.47.77]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-8a2c8ffc99bsm430968b3a.43.2026.10.23.00.56.17 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 23 Oct 2026 00:56:21 -0700 (PDT) From: Li Ximo To: Nicolas Ferre , Helge Deller , Alexandre Belloni , Claudiu Beznea Cc: linux-fbdev@vger.kernel.org, dri-devel@lists.freedesktop.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, Wang Haoran , Li Ximo Subject: [PATCH] video: fbdev: atmel_lcdfb: fix list_first_entry() on possibly empty modelist in probe Date: Fri, 23 Oct 2026 15:56:11 +0800 Message-Id: <20261023075611.3559095-1-lixicaicai@gmail.com> X-Mailer: git-send-email 2.25.1 X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit From: Wang Haoran list_first_entry() does not return NULL on an empty list; it returns a bogus pointer computed by container_of() from the list head. atmel_lcdfb_probe() initializes info->modelist with INIT_LIST_HEAD() and later takes its first entry with list_first_entry(), assuming atmel_lcdfb_of_init() populated it. However, atmel_lcdfb_of_init() drops the return value of fb_add_videomode() — unlike every other fallible call in the same function — so if fb_add_videomode() fails (its internal kmalloc can return -ENOMEM under memory pressure or fault injection), the list stays empty while of_init() reports success. The probe path then dereferences the bogus pointer in fb_videomode_to_var(&info->var, &modelist->mode). Because the bogus pointer lands inside the contiguous fb_info allocation, this may not fault immediately; instead it silently reads adjacent memory as a struct fb_videomode and programs garbage timing parameters into the LCD controller. This was found by code audit; we do not have Atmel hardware to reproduce it. Fix this on two levels: check the return value of fb_add_videomode() in atmel_lcdfb_of_init() so the failure is propagated (root cause), and use list_first_entry_or_null() in atmel_lcdfb_probe() with a NULL check that fails probe gracefully with -EINVAL (defense in depth), consistent with the surrounding error handling which bails out to stop_clk. Reported-by: Wang Haoran Reported-by: Li Ximo Signed-off-by: Wang Haoran --- drivers/video/fbdev/atmel_lcdfb.c | 13 ++++++++++--- 1 file changed, 10 insertions(+), 3 deletions(-) diff --git a/drivers/video/fbdev/atmel_lcdfb.c b/drivers/video/fbdev/atmel_lcdfb.c index 53f015699..6820a2400 100644 --- a/drivers/video/fbdev/atmel_lcdfb.c +++ b/drivers/video/fbdev/atmel_lcdfb.c @@ -1007,7 +1007,9 @@ static int atmel_lcdfb_of_init(struct atmel_lcdfb_info *sinfo) if (ret < 0) goto put_display_node; - fb_add_videomode(&fb_vm, &info->modelist); + ret = fb_add_videomode(&fb_vm, &info->modelist); + if (ret < 0) + goto put_display_node; put_display_node: of_node_put(display_np); @@ -1075,8 +1077,13 @@ static int atmel_lcdfb_probe(struct platform_device *pdev) } atmel_lcdfb_start_clock(sinfo); - modelist = list_first_entry(&info->modelist, - struct fb_modelist, list); + modelist = list_first_entry_or_null(&info->modelist, + struct fb_modelist, list); + if (!modelist) { + dev_err(dev, "no video mode available\n"); + ret = -EINVAL; + goto stop_clk; + } fb_videomode_to_var(&info->var, &modelist->mode); atmel_lcdfb_check_var(&info->var, info); -- 2.30.2