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authorTetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>2018-05-26 09:53:13 +0900
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2018-06-28 21:30:16 +0900
commit3d63b7e4ae0dc5e02d28ddd2fa1f945defc68d81 (patch)
tree4c72cbec570647876d8060aa4cb85cc4f3dfb796 /drivers/tty
parent7daf201d7fe8334e2d2364d4e8ed3394ec9af819 (diff)
n_tty: Fix stall at n_tty_receive_char_special().
syzbot is reporting stalls at n_tty_receive_char_special() [1]. This is because comparison is not working as expected since ldata->read_head can change at any moment. Mitigate this by explicitly masking with buffer size when checking condition for "while" loops. [1] https://syzkaller.appspot.com/bug?id=3d7481a346958d9469bebbeb0537d5f056bdd6e8 Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> Reported-by: syzbot <syzbot+18df353d7540aa6b5467@syzkaller.appspotmail.com> Fixes: bc5a5e3f45d04784 ("n_tty: Don't wrap input buffer indices at buffer size") Cc: stable <stable@vger.kernel.org> Cc: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'drivers/tty')
-rw-r--r--drivers/tty/n_tty.c13
1 files changed, 8 insertions, 5 deletions
diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c
index cbe98bc2b998..b279f8730e04 100644
--- a/drivers/tty/n_tty.c
+++ b/drivers/tty/n_tty.c
@@ -124,6 +124,8 @@ struct n_tty_data {
struct mutex output_lock;
};
+#define MASK(x) ((x) & (N_TTY_BUF_SIZE - 1))
+
static inline size_t read_cnt(struct n_tty_data *ldata)
{
return ldata->read_head - ldata->read_tail;
@@ -978,14 +980,15 @@ static void eraser(unsigned char c, struct tty_struct *tty)
}
seen_alnums = 0;
- while (ldata->read_head != ldata->canon_head) {
+ while (MASK(ldata->read_head) != MASK(ldata->canon_head)) {
head = ldata->read_head;
/* erase a single possibly multibyte character */
do {
head--;
c = read_buf(ldata, head);
- } while (is_continuation(c, tty) && head != ldata->canon_head);
+ } while (is_continuation(c, tty) &&
+ MASK(head) != MASK(ldata->canon_head));
/* do not partially erase */
if (is_continuation(c, tty))
@@ -1027,7 +1030,7 @@ static void eraser(unsigned char c, struct tty_struct *tty)
* This info is used to go back the correct
* number of columns.
*/
- while (tail != ldata->canon_head) {
+ while (MASK(tail) != MASK(ldata->canon_head)) {
tail--;
c = read_buf(ldata, tail);
if (c == '\t') {
@@ -1302,7 +1305,7 @@ n_tty_receive_char_special(struct tty_struct *tty, unsigned char c)
finish_erasing(ldata);
echo_char(c, tty);
echo_char_raw('\n', ldata);
- while (tail != ldata->read_head) {
+ while (MASK(tail) != MASK(ldata->read_head)) {
echo_char(read_buf(ldata, tail), tty);
tail++;
}
@@ -2411,7 +2414,7 @@ static unsigned long inq_canon(struct n_tty_data *ldata)
tail = ldata->read_tail;
nr = head - tail;
/* Skip EOF-chars.. */
- while (head != tail) {
+ while (MASK(head) != MASK(tail)) {
if (test_bit(tail & (N_TTY_BUF_SIZE - 1), ldata->read_flags) &&
read_buf(ldata, tail) == __DISABLED_CHAR)
nr--;