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-rw-r--r--lib/libc/gen/ttyname.c4
1 files changed, 4 insertions, 0 deletions
diff --git a/lib/libc/gen/ttyname.c b/lib/libc/gen/ttyname.c
index 02aa158..6628e3b 100644
--- a/lib/libc/gen/ttyname.c
+++ b/lib/libc/gen/ttyname.c
@@ -61,6 +61,10 @@ ttyname_r(int fd, char *buf, size_t len)
{
size_t used;
+ /* Don't write off the end of a zero-length buffer. */
+ if (len < 1)
+ return (ERANGE);
+
*buf = '\0';
/* Must be a terminal. */
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