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| author | Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> | 2018-05-26 02:53:13 +0200 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2018-06-28 14:30:16 +0200 |
| commit | 3d63b7e4ae0dc5e02d28ddd2fa1f945defc68d81 (patch) | |
| tree | 4c72cbec570647876d8060aa4cb85cc4f3dfb796 | |
| parent | Linux 4.18-rc2 (diff) | |
| download | linux-3d63b7e4ae0dc5e02d28ddd2fa1f945defc68d81.tar.xz linux-3d63b7e4ae0dc5e02d28ddd2fa1f945defc68d81.zip | |
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>
| -rw-r--r-- | drivers/tty/n_tty.c | 13 |
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--; |