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fix(session): Fix bitmap stride mismatch and out-of-bounds writes for xRDP compatibility #1252

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fix(session): Fix bitmap stride mismatch and out-of-bounds writes for xRDP compatibility #1252

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68070fb
fix(ironrdp-session): prevent buffer overflows in pixel data manipula…
amartyaa May 7, 2026
e37e242
Merge branch 'Devolutions:master' into master
amartyaa May 17, 2026
b7fdb8e
fix(ironrdp-session): Clip blit_rect for over-paint and made comparis…
amartyaa May 17, 2026
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2 changes: 1 addition & 1 deletion crates/ironrdp-session/Cargo.toml
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Original file line number Diff line number Diff line change
Expand Up @@ -14,7 +14,7 @@ categories.workspace = true

[lib]
doctest = false
test = false
# test = false

[features]
default = []
Expand Down
48 changes: 33 additions & 15 deletions crates/ironrdp-session/src/fast_path.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -192,6 +192,24 @@ impl Processor {
trace!("{update:?}");
buf.clear();

// The bitmap data dimensions (update.width x update.height) may differ
// from the destination rectangle dimensions (update.rectangle.width() x
// update.rectangle.height()). The apply_* methods use the rectangle's
// width for row stride, so we must use a rectangle whose dimensions
// match the actual bitmap data to avoid diagonal distortion.
//
// Per MS-RDPBCGR §2.2.9.1.1.3.1.2.2: "If the size of the bitmap data
// exceeds the size of the rectangle, the additional rows and columns
// MUST be discarded by the client." Clip to the smaller of the two.
let clipped_width = update.width.min(update.rectangle.width());
let clipped_height = update.height.min(update.rectangle.height());
let blit_rect = InclusiveRectangle {
left: update.rectangle.left,
top: update.rectangle.top,
right: update.rectangle.left + clipped_width.saturating_sub(1),
bottom: update.rectangle.top + clipped_height.saturating_sub(1),
};
Comment on lines +201 to +211

// Bitmap data is either compressed or uncompressed, depending
// on whether the BITMAP_COMPRESSION flag is present in the
// flags field.
Expand All @@ -211,7 +229,7 @@ impl Processor {
usize::from(update.width),
usize::from(update.height),
) {
Ok(()) => image.apply_rgb24(&buf, &update.rectangle, true)?,
Ok(()) => image.apply_rgb24(&buf, &blit_rect, true)?,
Err(err) => {
warn!("Invalid RDP6_BITMAP_STREAM: {err}");
update.rectangle.clone()
Expand All @@ -230,11 +248,11 @@ impl Processor {
usize::from(update.height),
usize::from(update.bits_per_pixel),
) {
Ok(RlePixelFormat::Rgb16) => image.apply_rgb16_bitmap(&buf, &update.rectangle)?,
Ok(RlePixelFormat::Rgb15) => image.apply_rgb15_bitmap(&buf, &update.rectangle)?,
Ok(RlePixelFormat::Rgb24) => image.apply_bgr24_bitmap(&buf, &update.rectangle)?,
Ok(RlePixelFormat::Rgb16) => image.apply_rgb16_bitmap(&buf, &blit_rect)?,
Ok(RlePixelFormat::Rgb15) => image.apply_rgb15_bitmap(&buf, &blit_rect)?,
Ok(RlePixelFormat::Rgb24) => image.apply_bgr24_bitmap(&buf, &blit_rect)?,
Ok(RlePixelFormat::Rgb8) => {
image.apply_rgb8_with_palette(&buf, &update.rectangle, self.palette.colors())?
image.apply_rgb8_with_palette(&buf, &blit_rect, self.palette.colors())?
}

Err(e) => {
Expand Down Expand Up @@ -266,11 +284,11 @@ impl Processor {
}

match update.bits_per_pixel {
8 => image.apply_rgb8_with_palette(&buf, &update.rectangle, self.palette.colors())?,
15 => image.apply_rgb15_bitmap(&buf, &update.rectangle)?,
16 => image.apply_rgb16_bitmap(&buf, &update.rectangle)?,
24 => image.apply_bgr24_bitmap(&buf, &update.rectangle)?,
32 => image.apply_rgb32_bitmap(&buf, PixelFormat::BgrX32, &update.rectangle)?,
8 => image.apply_rgb8_with_palette(&buf, &blit_rect, self.palette.colors())?,
15 => image.apply_rgb15_bitmap(&buf, &blit_rect)?,
16 => image.apply_rgb16_bitmap(&buf, &blit_rect)?,
24 => image.apply_bgr24_bitmap(&buf, &blit_rect)?,
32 => image.apply_rgb32_bitmap(&buf, PixelFormat::BgrX32, &blit_rect)?,
_ => {
warn!("Unsupported uncompressed bitmap depth: {bpp} bpp");
update.rectangle.clone()
Expand All @@ -280,13 +298,13 @@ impl Processor {
match update.bits_per_pixel {
8 => image.apply_rgb8_with_palette(
update.bitmap_data,
&update.rectangle,
&blit_rect,
self.palette.colors(),
)?,
15 => image.apply_rgb15_bitmap(update.bitmap_data, &update.rectangle)?,
16 => image.apply_rgb16_bitmap(update.bitmap_data, &update.rectangle)?,
24 => image.apply_bgr24_bitmap(update.bitmap_data, &update.rectangle)?,
32 => image.apply_rgb32_bitmap(update.bitmap_data, PixelFormat::BgrX32, &update.rectangle)?,
15 => image.apply_rgb15_bitmap(update.bitmap_data, &blit_rect)?,
16 => image.apply_rgb16_bitmap(update.bitmap_data, &blit_rect)?,
24 => image.apply_bgr24_bitmap(update.bitmap_data, &blit_rect)?,
32 => image.apply_rgb32_bitmap(update.bitmap_data, PixelFormat::BgrX32, &blit_rect)?,
_ => {
warn!("Unsupported uncompressed bitmap depth: {bpp} bpp");
update.rectangle.clone()
Expand Down
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