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fix: check unix-ioctl return value before reading winsize

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unix-ioctl returns NIL on failure, but the code still reads the
uninitialized alien winsize buffer, getting garbage values for
cols and rows (often 0 for rows). Now checks 'ok' before reading.
This commit is contained in:
Amr Gharbeia
2026-05-14 14:47:43 -04:00
parent aa73171c30
commit 9a54b7ade6
2 changed files with 29 additions and 34 deletions
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32
src/backend/modern.lisp
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@@ -181,31 +181,29 @@ as a fallback when a keyword is not in *named-colors*.")
;; ioctl on stdout fd — fast, correct after SIGWINCH at runtime.
(multiple-value-bind (cols rows)
(ignore-errors
(let* ((+tiocgwinsz+ 21523) ; 0x5413 on Linux
(winsize (sb-alien:make-alien sb-alien:unsigned-short 4)))
(let* ((winsize (sb-alien:make-alien sb-alien:unsigned-short 4)))
(unwind-protect
(progn
(sb-unix:unix-ioctl (sb-sys:fd-stream-fd (backend-output-stream b))
+tiocgwinsz+
(sb-alien:alien-sap winsize))
(values (sb-alien:deref winsize 1) ;; cols
(sb-alien:deref winsize 0))) ;; rows
(let ((ok (sb-unix:unix-ioctl
(sb-sys:fd-stream-fd (backend-output-stream b))
21523 (sb-alien:alien-sap winsize))))
(when ok
(values (sb-alien:deref winsize 1) ;; cols
(sb-alien:deref winsize 0)))) ;; rows
(sb-alien:free-alien winsize))))
(when (and cols rows (> cols 0) (> rows 0))
(values cols rows)))
;; Direct ioctl on /dev/tty — opens the real controlling terminal.
;; Direct ioctl on /dev/tty.
(ignore-errors
(let ((tty-fd (sb-unix:unix-open "/dev/tty" 0 0))) ; O_RDONLY
(let ((tty-fd (sb-unix:unix-open "/dev/tty" 0 0)))
(when (and tty-fd (numberp tty-fd) (> tty-fd 0))
(unwind-protect
(let* ((winsize (sb-alien:make-alien sb-alien:unsigned-short 4)))
(sb-unix:unix-ioctl tty-fd 21523 (sb-alien:alien-sap winsize))
(let ((cols (sb-alien:deref winsize 1))
(rows (sb-alien:deref winsize 0)))
(sb-alien:free-alien winsize)
(when (and (integerp cols) (integerp rows)
(> cols 0) (> rows 0))
(values cols rows))))
(let ((ok (sb-unix:unix-ioctl tty-fd 21523
(sb-alien:alien-sap winsize))))
(when ok
(let ((cols (sb-alien:deref winsize 1))
(rows (sb-alien:deref winsize 0)))
(values cols rows)))))
(sb-unix:unix-close tty-fd)))))
(values 80 24)))