7.2-stable review patch. If anyone has any objections, please let me know. ------------------ From: Harry Wentland commit 622b4e8505aa7453a53d17fa3a288871f270fc8b upstream. [Why] dp_link_settings_read() passed strlen() of each format string as the size argument to snprintf() and then advanced rd_buf_ptr by that same fixed amount. The format-string length has no relation to the formatted output length, so snprintf() truncated each field at a NUL it wrote inside the buffer while the pointer was advanced past it. The result is a buffer peppered with embedded NUL bytes and fields that are silently cut short, so the data read back from the debugfs node does not reflect the actual link settings. [How] Use scnprintf() with the real remaining buffer size (rd_buf_size - (rd_buf_ptr - rd_buf)) and advance rd_buf_ptr by its return value, which is the number of characters actually written. This both bounds each write to the space left in rd_buf and keeps the output a single, properly terminated string. The now-unused str_len local is removed. Fixes: 41db5f1931ec ("drm/amd/display: set-read link rate and lane count through debugfs") Assisted-by: Copilot:claude-opus-4.8 Signed-off-by: Harry Wentland Reviewed-by: Alex Hung Signed-off-by: Alex Deucher (cherry picked from commit 43b9f0f18693c7f7b75613f3aeae25fa2b4e2f76) Cc: stable@vger.kernel.org Signed-off-by: Greg Kroah-Hartman --- drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_debugfs.c | 20 +++++--------- 1 file changed, 8 insertions(+), 12 deletions(-) --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_debugfs.c +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_debugfs.c @@ -196,7 +196,6 @@ static ssize_t dp_link_settings_read(str char *rd_buf_ptr = NULL; const uint32_t rd_buf_size = 100; uint32_t result = 0; - uint8_t str_len = 0; int r; if (*pos & 3 || size & 3) @@ -208,29 +207,26 @@ static ssize_t dp_link_settings_read(str rd_buf_ptr = rd_buf; - str_len = strlen("Current: %d 0x%x %d "); - snprintf(rd_buf_ptr, str_len, "Current: %d 0x%x %d ", + rd_buf_ptr += scnprintf(rd_buf_ptr, rd_buf_size - (rd_buf_ptr - rd_buf), + "Current: %d 0x%x %d ", link->cur_link_settings.lane_count, link->cur_link_settings.link_rate, link->cur_link_settings.link_spread); - rd_buf_ptr += str_len; - str_len = strlen("Verified: %d 0x%x %d "); - snprintf(rd_buf_ptr, str_len, "Verified: %d 0x%x %d ", + rd_buf_ptr += scnprintf(rd_buf_ptr, rd_buf_size - (rd_buf_ptr - rd_buf), + "Verified: %d 0x%x %d ", link->verified_link_cap.lane_count, link->verified_link_cap.link_rate, link->verified_link_cap.link_spread); - rd_buf_ptr += str_len; - str_len = strlen("Reported: %d 0x%x %d "); - snprintf(rd_buf_ptr, str_len, "Reported: %d 0x%x %d ", + rd_buf_ptr += scnprintf(rd_buf_ptr, rd_buf_size - (rd_buf_ptr - rd_buf), + "Reported: %d 0x%x %d ", link->reported_link_cap.lane_count, link->reported_link_cap.link_rate, link->reported_link_cap.link_spread); - rd_buf_ptr += str_len; - str_len = strlen("Preferred: %d 0x%x %d "); - snprintf(rd_buf_ptr, str_len, "Preferred: %d 0x%x %d\n", + rd_buf_ptr += scnprintf(rd_buf_ptr, rd_buf_size - (rd_buf_ptr - rd_buf), + "Preferred: %d 0x%x %d\n", link->preferred_link_setting.lane_count, link->preferred_link_setting.link_rate, link->preferred_link_setting.link_spread);