From: Srinivasan Shanmugam Date: Fri, 21 Nov 2025 10:58:20 +0000 (+0530) Subject: drm/amdgpu: Fix CPER ring debugfs read buffer overflow risk X-Git-Url: https://gentwo.org/gitweb/?a=commitdiff_plain;h=93c19634f72fb32284e5775b44e4076c059d8e67;p=linux%2F.git drm/amdgpu: Fix CPER ring debugfs read buffer overflow risk The CPER ring debugfs read code always writes a 12-byte header when the file is read for the first time (*offset == 0): copy_to_user(buf, ring_header, 12); But the code never checks whether the user buffer (@size) is at least 12 bytes long. After writing the 12-byte header, the code then gives the full original @size to the CPER payload handler: record_req->buf_size = size; This means the function can write: 12 bytes (header) + payload bytes (up to @size) into a buffer that is only @size bytes big. In other words, the kernel may write more data than the user asked for. This can overflow the user buffer. The fix is: - If the user buffer is smaller than 12 bytes on the first read, return -EINVAL instead of copying the header. - After writing the 12-byte header, subtract 12 from @size and pass the reduced size to record_req->buf_size. This ensures the CPER payload only uses the remaining free space in the buffer. Reads after the first one (*offset != 0) do not write the header, so their behavior stays exactly the same. The only user-visible change is that tiny buffers now fail safely instead of risking an overflow. Fixes: drivers/gpu/drm/amd/amdgpu/amdgpu_ring.c:523 amdgpu_ras_cper_debugfs_read() warn: userbuf overflow? is 'ring_header_size' <= 'size' Fixes: 527e3d40339b ("drm/amd/ras: Add CPER ring read for uniras") Reported by: Dan Carpenter Cc: Xiang Liu Cc: Tao Zhou Cc: Yang Wang Cc: Christian König Cc: Alex Deucher Signed-off-by: Srinivasan Shanmugam Reviewed-by: Tao Zhou Signed-off-by: Alex Deucher --- diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ring.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_ring.c index cd8873c6931a..c596b6df2e2d 100644 --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ring.c +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ring.c @@ -520,9 +520,14 @@ static ssize_t amdgpu_ras_cper_debugfs_read(struct file *f, char __user *buf, return -ENOMEM; if (!(*offset)) { + /* Need at least 12 bytes for the header on the first read */ + if (size < ring_header_size) + return -EINVAL; + if (copy_to_user(buf, ring_header, ring_header_size)) return -EFAULT; buf += ring_header_size; + size -= ring_header_size; } r = amdgpu_ras_mgr_handle_ras_cmd(ring->adev,