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| author | Jiri Slaby <jslaby@suse.cz> | 2014-05-05 10:24:08 +0200 |
|---|---|---|
| committer | Jiri Kosina <jkosina@suse.cz> | 2014-05-13 10:40:57 +0200 |
| commit | 9ec28a07c548e804eeaeb0f37450ac5320df10bd (patch) | |
| tree | a3ffe7a6b039f44ae205c696465be23be929df66 | |
| parent | b960221f715465be39ef208887de6db4b107bba0 (diff) | |
n_tty: Fix n_tty_write crash when echoing in raw mode
(bnc#871252 bnc#875690 CVE-2014-0196).
| -rw-r--r-- | patches.fixes/n_tty-Fix-n_tty_write-crash-when-echoing-in-raw-mode.patch | 76 | ||||
| -rw-r--r-- | series.conf | 1 |
2 files changed, 77 insertions, 0 deletions
diff --git a/patches.fixes/n_tty-Fix-n_tty_write-crash-when-echoing-in-raw-mode.patch b/patches.fixes/n_tty-Fix-n_tty_write-crash-when-echoing-in-raw-mode.patch new file mode 100644 index 0000000000..f4f31ecdee --- /dev/null +++ b/patches.fixes/n_tty-Fix-n_tty_write-crash-when-echoing-in-raw-mode.patch @@ -0,0 +1,76 @@ +From: Peter Hurley <peter@hurleysoftware.com> +Date: Tue, 29 Apr 2014 12:38:36 -0400 +Subject: n_tty: Fix n_tty_write crash when echoing in raw mode +Patch-mainline: submitted May 5 2014 +References: bnc#871252 bnc#875690 CVE-2014-0196 + +The tty atomic_write_lock does not provide an exclusion guarantee for +the tty driver if the termios settings are LECHO & !OPOST. And since +it is unexpected and not allowed to call TTY buffer helpers like +tty_insert_flip_string concurrently, this may lead to crashes when +concurrect writers call pty_write. In that case the following two +writers: +* the ECHOing from a workqueue and +* pty_write from the process +race and can overflow the corresponding TTY buffer like follows. + +If we look into tty_insert_flip_string_fixed_flag, there is: + int space = __tty_buffer_request_room(port, goal, flags); + struct tty_buffer *tb = port->buf.tail; + ... + memcpy(char_buf_ptr(tb, tb->used), chars, space); + ... + tb->used += space; + +so the race of the two can result in something like this: + A B +__tty_buffer_request_room + __tty_buffer_request_room +memcpy(buf(tb->used), ...) +tb->used += space; + memcpy(buf(tb->used), ...) ->BOOM + +B's memcpy is past the tty_buffer due to the previous A's tb->used +increment. + +Since the N_TTY line discipline input processing can output +concurrently with a tty write, obtain the N_TTY ldisc output_lock to +serialize echo output with normal tty writes. This ensures the tty +buffer helper tty_insert_flip_string is not called concurrently and +everything is fine. + +Note that this is nicely reproducible by an ordinary user using +forkpty and some setup around that (raw termios + ECHO). And it is +present in kernels at least after commit +d945cb9cce20ac7143c2de8d88b187f62db99bdc (pty: Rework the pty layer to +use the normal buffering logic) in 2.6.31-rc3. + +js: add more info to the commit log +js: switch to bool +js: lock unconditionally +js: lock only the tty->ops->write call + +References: CVE-2014-0196 +Reported-and-tested-by: Jiri Slaby <jslaby@suse.cz> +Signed-off-by: Peter Hurley <peter@hurleysoftware.com> +Signed-off-by: Jiri Slaby <jslaby@suse.cz> +Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> +Cc: Linus Torvalds <torvalds@linux-foundation.org> +Cc: Alan Cox <alan@lxorguk.ukuu.org.uk> +Cc: <stable@vger.kernel.org> +--- + drivers/tty/n_tty.c | 2 ++ + 1 file changed, 2 insertions(+) + +--- a/drivers/tty/n_tty.c ++++ b/drivers/tty/n_tty.c +@@ -2017,7 +2017,9 @@ static ssize_t n_tty_write(struct tty_st + tty->ops->flush_chars(tty); + } else { + while (nr > 0) { ++ mutex_lock(&tty->output_lock); + c = tty->ops->write(tty, b, nr); ++ mutex_unlock(&tty->output_lock); + if (c < 0) { + retval = c; + goto break_out; diff --git a/series.conf b/series.conf index a473ba8de6..e5c5c3a9a5 100644 --- a/series.conf +++ b/series.conf @@ -13719,6 +13719,7 @@ ########################################################## patches.suse/revert-U6715-16550A-serial-driver-support.patch patches.fixes/printk-fix-softlockups-during-heavy-printing.patch + patches.fixes/n_tty-Fix-n_tty_write-crash-when-echoing-in-raw-mode.patch ######################################################## # Other driver fixes |