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console: a bare ESC[m is a reset, and OSC sequences are consumed

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Two ANSI bugs, both found by running fastfetch rather than by reading the
parser, and both invisible to anything that spells its escapes out in full.

ESC[m with no parameters means ESC[0m. ECMA-48 is explicit that an omitted
parameter takes its default and SGR's default is 0, and sgr() iterated its
parameter list -- which is empty in exactly that case, so the loop body never
ran and the reset was silently dropped.

Programs emit the bare form constantly. fastfetch writes "\x1b[32m1%\x1b[m", so
everything after the first coloured character stayed green forever. With a
background colour it is much worse: its palette swatch sets a white background
and resets, the reset did nothing, and the console went white-on-white and
stayed there -- filling the screen with white rectangles as it scrolled, which
looks like a corrupted framebuffer rather than one missing branch.

OSC sequences were not a state at all, so ESC ] fell through and the payload
printed as text: a hyperlinked path arrived as "Disk (]8;;file:///\]8;;\)".
Nothing here acts on an operating-system command -- there is no window title and
no hyperlink to follow -- but *discarding* one is not optional, because the
alternative is printing somebody's URL into the middle of their output. ESC \
ends it, and an ESC followed by anything else is handed back to the escape state
rather than eaten, so a malformed OSC does not swallow the sequence after it.

Verified by screendumping the framebuffer after two consecutive fastfetch runs:
identical output both times, near-white coverage down from most of the screen to
2% (the palette swatch's own white cell), and the disk line reading "Disk (/)".

Also installs docs/branding/Ascii/ascii_50.txt as /usr/share/schos/logo.txt --
Shift as characters, at the width that leaves room for an info block on an
80-column console. Installed from the branding directory rather than copied into
sysroot by hand, so there is one source.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01VQ7Qx8E1q1M1bbCq8QLHS2
This commit is contained in:
Nexoniarz 2026-09-12 19:38:00 +02:00
commit 1754cbf1aa
8 changed files with 292 additions and 4 deletions
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42
kernel/core/console.c
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@ -217,7 +217,11 @@ static uint32 cons_bg = CONS_DEFAULT_BG;
static int cons_bold = 0;
// Escape parser state.
enum { E_NORMAL, E_ESC, E_CSI };
// E_OSC and E_OSC_ESC exist for hyperlinks. A terminal that does not follow
// them must still *consume* them, or the URL is printed as text -- which is
// what "Disk (]8;;file:///\]8;;\): 4.6 MiB" was: fastfetch wrapping a path in
// OSC 8, and this console spelling it out.
enum { E_NORMAL, E_ESC, E_CSI, E_OSC, E_OSC_ESC };
static int esc_state = E_NORMAL;
static int esc_parm[8];
static int esc_nparm;
@ -302,7 +306,19 @@ glyph_for(uint32 cp)
static void
sgr(void)
{
for (int i = 0; i < esc_nparm; i++) {
// "ESC[m" with no parameters means ESC[0m -- reset -- and ECMA-48 says so for
// every CSI: an omitted parameter takes its default, and SGR's default is 0.
//
// This loop used to start at a count of zero and therefore do nothing, so a
// bare reset was silently dropped. Programs emit it constantly: fastfetch
// writes "\x1b[32m1%\x1b[m", and with the reset ignored everything after the
// first coloured character stayed green forever. Worse with background
// colours -- its palette swatch sets a white background and resets, so the
// whole console went white-on-white and stayed there, which looks like a
// corrupted framebuffer rather than a missing branch.
int nparm = esc_nparm ? esc_nparm : 1; // esc_parm[0] is already 0
for (int i = 0; i < nparm; i++) {
int p = esc_parm[i];
if (p == 0) {
@ -392,6 +408,10 @@ gfx_feed(int c)
for (int i = 0; i < 8; i++) esc_parm[i] = 0;
return;
}
if (c == ']') { // OSC: swallow it, see below
esc_state = E_OSC;
return;
}
esc_state = E_NORMAL;
if (c == 'c') { // RIS -- full reset
cons_fg = CONS_DEFAULT_FG;
@ -400,6 +420,24 @@ gfx_feed(int c)
}
return; // other two-byte escapes: ignored
// An operating-system command runs until BEL or until ST (ESC \). Nothing
// here acts on one -- there is no window title to set and no hyperlink to
// follow -- but discarding the payload is not optional: the alternative is
// printing somebody's URL into the middle of their output.
case E_OSC:
if (c == '\a') { esc_state = E_NORMAL; return; }
if (c == '\x1b') { esc_state = E_OSC_ESC; return; }
return;
case E_OSC_ESC:
// ESC \ ends it; ESC anything-else means the OSC was malformed and a new
// escape has started, so hand the byte to the ESC state rather than eating
// it. Dropping it would lose the sequence that follows.
if (c == '\\') { esc_state = E_NORMAL; return; }
esc_state = E_ESC;
gfx_feed(c);
return;
case E_CSI:
if (c == '?') { esc_private = 1; return; }
if (c >= '0' && c <= '9') {