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([2a02:908:1b4:dac0:85a8:ed04:ac09:e3e0]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-b87959c9a14sm804992266b.45.2026.01.18.05.47.37 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 18 Jan 2026 05:47:38 -0800 (PST) From: Osama Abdelkader To: Simona Vetter , Helge Deller , Thomas Zimmermann , Lee Jones , Murad Masimov , Quanmin Yan , Yongzhen Zhang , Osama Abdelkader , linux-fbdev@vger.kernel.org, dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org Cc: syzbot+55e03490a0175b8dd81d@syzkaller.appspotmail.com Subject: [PATCH] fbdev: Fix slab-out-of-bounds read in fb_pad_unaligned_buffer Date: Sun, 18 Jan 2026 14:47:28 +0100 Message-ID: <20260118134735.11507-1-osama.abdelkader@gmail.com> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: linux-fbdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit The function fb_pad_unaligned_buffer() was reading idx+1 bytes per row from the source buffer, but when mod == 0 (font width is a multiple of 8 bits), the source buffer only has idx bytes per row. This caused a slab-out-of-bounds read when accessing src[idx] after the inner loop. Fix this by only reading the extra byte when mod != 0, ensuring we never read beyond the source buffer boundaries. This fixes the KASAN slab-out-of-bounds read reported by syzkaller: https://syzkaller.appspot.com/bug?extid=55e03490a0175b8dd81d Reported-by: syzbot+55e03490a0175b8dd81d@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=55e03490a0175b8dd81d Signed-off-by: Osama Abdelkader --- drivers/video/fbdev/core/fbmem.c | 18 ++++++++++-------- 1 file changed, 10 insertions(+), 8 deletions(-) diff --git a/drivers/video/fbdev/core/fbmem.c b/drivers/video/fbdev/core/fbmem.c index eff757ebbed1..a0c4932a6758 100644 --- a/drivers/video/fbdev/core/fbmem.c +++ b/drivers/video/fbdev/core/fbmem.c @@ -113,15 +113,17 @@ void fb_pad_unaligned_buffer(u8 *dst, u32 d_pitch, u8 *src, u32 idx, u32 height, dst[j+1] = tmp; src++; } - tmp = dst[idx]; - tmp &= mask; - tmp |= *src >> shift_low; - dst[idx] = tmp; - if (shift_high < mod) { - tmp = *src << shift_high; - dst[idx+1] = tmp; + if (mod) { + tmp = dst[idx]; + tmp &= mask; + tmp |= *src >> shift_low; + dst[idx] = tmp; + if (shift_high < mod) { + tmp = *src << shift_high; + dst[idx+1] = tmp; + } + src++; } - src++; dst += d_pitch; } } -- 2.43.0