Messages in this thread Patch in this message | | | From | Mazin Al Haddad <> | Subject | [PATCH] tty: n_gsm: fix missing assignment of gsm->receive() in gsmld_attach_gsm() | Date | Wed, 10 Aug 2022 06:12:52 +0300 |
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Fixes a bug reported by syzbot. A null pointer dereference can happen when attempting to access the "gsm->receive()" function in gsmld_receive_buf(). Currently, the "gsm->receive()" function is only set after a call to the GSMIO_SETCONF ioctl. Since the gsmld_receive_buf() function can be accessed without the need to call the line discipline ioctl (GSMIO_SETCONF), the gsm->receive() function will not be set and a NULL pointer dereference will occur.
Fix this by setting the gsm->receive() function when the line discipline is being attached to the terminal device, inside gsmld_attach_gsm(). This will guarantee that the function is assigned and a call to TIOCSTI, which calls gsmld_receive_buf(), will not reference a null pointer.
Call Trace: <TASK> gsmld_receive_buf+0x1c2/0x2f0 drivers/tty/n_gsm.c:2861 tiocsti drivers/tty/tty_io.c:2293 [inline] tty_ioctl+0xa75/0x15d0 drivers/tty/tty_io.c:2692 vfs_ioctl fs/ioctl.c:51 [inline] __do_sys_ioctl fs/ioctl.c:870 [inline] __se_sys_ioctl fs/ioctl.c:856 [inline] __x64_sys_ioctl+0x193/0x200 fs/ioctl.c:856 do_syscall_x64 arch/x86/entry/common.c:50 [inline] do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80 entry_SYSCALL_64_after_hwframe+0x63/0xcd
Fixes: 01aecd917114 ("tty: n_gsm: fix tty registration before control channel open") Reported-and-tested-by: syzbot+e3563f0c94e188366dbb@syzkaller.appspotmail.com Signed-off-by: Mazin Al Haddad <mazinalhaddad05@gmail.com> --- drivers/tty/n_gsm.c | 5 +++++ 1 file changed, 5 insertions(+)
diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c index caa5c14ed57f..1d74dd9d70d0 100644 --- a/drivers/tty/n_gsm.c +++ b/drivers/tty/n_gsm.c @@ -2825,6 +2825,11 @@ static void gsmld_attach_gsm(struct tty_struct *tty, struct gsm_mux *gsm) /* Turn off tty XON/XOFF handling to handle it explicitly. */ gsm->old_c_iflag = tty->termios.c_iflag; tty->termios.c_iflag &= (IXON | IXOFF); + + if (gsm->encoding == 0) + gsm->receive = gsm0_receive; + else + gsm->receive = gsm1_receive; } /** -- 2.37.1
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