Messages in this thread Patch in this message | ![/](/images/icornerl.gif) | | Date | Sat, 20 Apr 2024 20:12:32 +0900 | From | Tetsuo Handa <> | Subject | [PATCH v2] tty: n_gsm: restrict tty devices to attach |
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syzbot is reporting sleep in atomic context, for gsmld_write() is calling con_write() with spinlock held and IRQs disabled.
Since n_gsm is designed to be used for serial port [1], reject attaching to virtual consoles and PTY devices, by checking tty's device major/minor numbers at gsmld_open().
Starke, Daniel commented
Our application of this protocol is only with specific modems to enable circuit switched operation (handling calls, selecting/querying networks, etc.) while doing packet switched communication (i.e. IP traffic over PPP). The protocol was developed for such use cases.
at [2], but it seems that nobody can define allow list for device numbers where this protocol should accept. Therefore, this patch defines deny list for device numbers.
Greg Kroah-Hartman is not happy with use of hard-coded magic numbers [3], but I don't think we want to update include/uapi/linux/major.h and add include/uapi/linux/minor.h just for fixing this bug.
Link: https://www.kernel.org/doc/html/v6.8/driver-api/tty/n_gsm.html [1] Link: https://lkml.kernel.org/r/DB9PR10MB588170E923A6ED8B3D6D9613E0CBA@DB9PR10MB5881.EURPRD10.PROD.OUTLOOK.COM [2] Link: https://lkml.kernel.org/r/2024020615-stir-dragster-aeb6@gregkh [3] Reported-by: syzbot <syzbot+dbac96d8e73b61aa559c@syzkaller.appspotmail.com> Closes: https://syzkaller.appspot.com/bug?extid=dbac96d8e73b61aa559c Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> --- Adding LSM ML to CC list in order to ask for comments if Greg again complained that we don't want to add sanity check on the kernel side. I agree that we should fix fuzzers if fuzzers are writing random data to /dev/mem or /dev/kmem . But for example https://lkml.kernel.org/r/CAADnVQJQvcZOA_BbFxPqNyRbMdKTBSMnf=cKvW7NJ8LxxP54sA@mail.gmail.com demonstrates that developers try to fix bugs on the kernel side rather than tell fuzzers not to do artificial things.
drivers/tty/n_gsm.c | 12 ++++++++++++ 1 file changed, 12 insertions(+)
diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c index 4036566febcb..14581483af78 100644 --- a/drivers/tty/n_gsm.c +++ b/drivers/tty/n_gsm.c @@ -3623,6 +3623,7 @@ static void gsmld_close(struct tty_struct *tty) static int gsmld_open(struct tty_struct *tty) { struct gsm_mux *gsm; + int major; if (!capable(CAP_NET_ADMIN)) return -EPERM; @@ -3630,6 +3631,17 @@ static int gsmld_open(struct tty_struct *tty) if (tty->ops->write == NULL) return -EINVAL; + major = tty->driver->major; + /* Reject Virtual consoles */ + if (major == 4 && tty->driver->minor_start == 1) + return -EINVAL; + /* Reject Unix98 PTY masters/slaves */ + if (major >= 128 && major <= 143) + return -EINVAL; + /* Reject BSD PTY masters/slaves */ + if (major >= 2 && major <= 3) + return -EINVAL; + /* Attach our ldisc data */ gsm = gsm_alloc_mux(); if (gsm == NULL) -- 2.18.4
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