Date: Tue, 29 Oct 2019 01:43:10 +0000 From: bugzilla-noreply@freebsd.org To: bugs@FreeBSD.org Subject: [Bug 241559] cat(1) endless loop when writing to special device file Message-ID: <bug-241559-227@https.bugs.freebsd.org/bugzilla/>
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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=3D241559 Bug ID: 241559 Summary: cat(1) endless loop when writing to special device file Product: Base System Version: 12.1-RELEASE Hardware: Any OS: Any Status: New Severity: Affects Only Me Priority: --- Component: bin Assignee: bugs@FreeBSD.org Reporter: sigsys@gmail.com Using cat to write to a disk directly loops forever when it reaches the end= of the disk and there's still data to write (like when using /dev/zero or /dev/random for example). write() returns 0 (without setting errno) when t= hat happens (one of the very rare cases where that can happen it seems) and cat handles this by retrying the write forever. It would be better to error ou= t in this case AFAIK. There must be tons of programs that react very poorly when making them write to a device file directly like that, but one might expect that cat always work (more or less). $ mdconfig -s 1m -u 10 $ cat /dev/zero > /dev/md10 # loops forever cp seems to handle it better: $ cp /dev/zero /dev/md10 cp: /dev/md10: No error: 0 Which isn't a very good error message but still better since it doesn't loop forever. With this change: Index: bin/cat/cat.c =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D --- bin/cat/cat.c (revision 354128) +++ bin/cat/cat.c (working copy) @@ -327,7 +327,7 @@ } while ((nr =3D read(rfd, buf, bsize)) > 0) for (off =3D 0; nr; nr -=3D nw, off +=3D nw) - if ((nw =3D write(wfd, buf + off, (size_t)nr)) < 0) + if ((nw =3D write(wfd, buf + off, (size_t)nr)) <=3D= 0) err(1, "stdout"); if (nr < 0) { warn("%s", filename); It errors out like cp instead: $ cat /dev/zero > /dev/md10 cat: stdout: No error: 0 That's when cat is in "raw mode". In "cooked mode", it already errors out,= but it picks up a bogus errno for it: $ cat -v /dev/zero > /dev/md10 cat: stdout: Inappropriate ioctl for device Which comes from an isatty() call in stdio. errno should be saved at some point, dunno if it should be done by cat or stdio (before its call to isatt= y() in __smakebuf()). Not very important though I guess. --=20 You are receiving this mail because: You are the assignee for the bug.=
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