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Wed, 01 Jul 2026 16:17:10 -0700 (PDT) From: Melbin K Mathew To: deller@gmx.de Cc: linux-fbdev@vger.kernel.org, dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, Melbin K Mathew , stable@vger.kernel.org Subject: [PATCH v2 1/2] fbdev: bound mode sysfs output to the sysfs buffer Date: Thu, 2 Jul 2026 01:17:05 +0200 Message-Id: <20260701231706.234715-2-mlbnkm1@gmail.com> X-Mailer: git-send-email 2.39.5 In-Reply-To: <20260701221757.231490-1-mlbnkm1@gmail.com> References: <20260701221757.231490-1-mlbnkm1@gmail.com> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit mode_string() uses snprintf() which can return a value larger than the remaining buffer space. show_modes() accumulates the return value into i without checking whether i has reached PAGE_SIZE, causing the offset to advance past the sysfs buffer if the modelist is long enough. Add a size parameter to mode_string() and use scnprintf() to return only the bytes actually written. Add an early return when offset already exceeds the buffer. In show_modes(), stop accumulating once the buffer is full. Cc: stable@vger.kernel.org Signed-off-by: Melbin K Mathew --- drivers/video/fbdev/core/fbsysfs.c | 15 ++++++++++----- 1 file changed, 10 insertions(+), 5 deletions(-) diff --git a/drivers/video/fbdev/core/fbsysfs.c b/drivers/video/fbdev/core/fbsysfs.c index ea196603c7..af21dc5052 100644 --- a/drivers/video/fbdev/core/fbsysfs.c +++ b/drivers/video/fbdev/core/fbsysfs.c @@ -27,12 +27,15 @@ static int activate(struct fb_info *fb_info, struct fb_var_screeninfo *var) return 0; } -static int mode_string(char *buf, unsigned int offset, +static int mode_string(char *buf, size_t size, unsigned int offset, const struct fb_videomode *mode) { char m = 'U'; char v = 'p'; + if (offset >= size) + return 0; + if (mode->flag & FB_MODE_IS_DETAILED) m = 'D'; if (mode->flag & FB_MODE_IS_VESA) @@ -45,7 +48,7 @@ static int mode_string(char *buf, unsigned int offset, if (mode->vmode & FB_VMODE_DOUBLE) v = 'd'; - return snprintf(&buf[offset], PAGE_SIZE - offset, "%c:%dx%d%c-%d\n", + return scnprintf(&buf[offset], size - offset, "%c:%dx%d%c-%d\n", m, mode->xres, mode->yres, v, mode->refresh); } @@ -64,7 +67,7 @@ static ssize_t store_mode(struct device *device, struct device_attribute *attr, list_for_each_entry(modelist, &fb_info->modelist, list) { mode = &modelist->mode; - i = mode_string(mstr, 0, mode); + i = mode_string(mstr, sizeof(mstr), 0, mode); if (strncmp(mstr, buf, max(count, i)) == 0) { var = fb_info->var; @@ -86,7 +89,7 @@ static ssize_t show_mode(struct device *device, struct device_attribute *attr, if (!fb_info->mode) return 0; - return mode_string(buf, 0, fb_info->mode); + return mode_string(buf, PAGE_SIZE, 0, fb_info->mode); } static ssize_t store_modes(struct device *device, @@ -136,7 +139,9 @@ static ssize_t show_modes(struct device *device, struct device_attribute *attr, i = 0; list_for_each_entry(modelist, &fb_info->modelist, list) { mode = &modelist->mode; - i += mode_string(buf, i, mode); + i += mode_string(buf, PAGE_SIZE, i, mode); + if (i >= PAGE_SIZE - 1) + break; } return i; } -- 2.39.5