From 6fbb9b7d3b2b43e69ca3ce56823fdb9f65a74890 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Daniel=20Ekl=C3=B6f?= Date: Wed, 28 Jan 2026 09:21:57 +0100 Subject: [PATCH] sixel: force a height of at least one sixel when explicitly resizing Applications often prefix the sixel with a raster attributes (RA) sequence, where they tell us how large the sixel is. Strictly speaking, this just tells us the size of the area to clear, but we use it as a hint and pre-allocates the image buffer. It's important to stress that it is valid to emit a MxN RA, and then write sixel data outside of that area. Foot handles this, in _most_ cases. We didn't handle the corner case Mx0. I.e. a width > 0, but height == 0. No image buffer was allocated, and we also failed to detect a resize was necessary when the application started printing sixel data. Much of this is for performance reason; we only check the minimum necessary. For example, we only check if going outside the pre-allocated *column* while printing sixels. *Rows* are checked on a graphical newline. In other words, the *current* row has to be valid when writing sixels. And in case of Mx0, it wasn't. Fix by forcing a height of at least one sixel (typically 6 pixels). Closes #2267 --- CHANGELOG.md | 3 +++ sixel.c | 3 +++ 2 files changed, 6 insertions(+) diff --git a/CHANGELOG.md b/CHANGELOG.md index a69f58b8..ce1a7d8c 100644 --- a/CHANGELOG.md +++ b/CHANGELOG.md @@ -124,9 +124,12 @@ * Regression: visual glitches in rare circumstances. * Key release events for shortcuts being sent to the client application (kitty keyboard protocol only) ([#2257][2257]). +* Crash when application emits sixel RA with a height of 0, a width > + 0, and then starts writing sixel data ([#2267][2267]). [2232]: https://codeberg.org/dnkl/foot/issues/2232 [2257]: https://codeberg.org/dnkl/foot/issues/2257 +[2267]: https://codeberg.org/dnkl/foot/issues/2267 ### Security diff --git a/sixel.c b/sixel.c index 294864fd..187f1348 100644 --- a/sixel.c +++ b/sixel.c @@ -1559,6 +1559,9 @@ resize(struct terminal *term, int new_width_mutable, int new_height_mutable) new_height_mutable = term->sixel.max_height; } + if (unlikely(new_height_mutable == 0)) { + new_height_mutable = 6 * term->sixel.pan; + } uint32_t *old_data = term->sixel.image.data; const int old_width = term->sixel.image.width;