RE: [PATCH] tty: n_gsm: fix missing assignment of gsm->receive() in gsmld_attach_gsm()

RE: [PATCH] tty: n_gsm: fix missing assignment of gsm->receive() in gsmld_attach_gsm()

[Starke, Daniel]

> 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.

In my opinion there are only two possible ways to fix this:
a) Move the gsm->receive initialization from gsm_activate_mux() to
gsmld_attach_gsm().
b) Avoid calling gsm->receive in gsmld_receive_buf() if not initialized.

The current code might assume that gsm->receive is only called after MUX
activation. Therefore, variant a) may break the code in other places.
I see no need to initialize gsm->receive in gsm_activate_mux() and
gsmld_attach_gsm().

Best regards,
Daniel Starke

RE: [PATCH] tty: n_gsm: fix missing assignment of gsm->receive() in gsmld_attach_gsm()

[Starke, Daniel]

> 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.

In my opinion there are only two possible ways to fix this:
a) Move the gsm->receive initialization from gsm_activate_mux() to
gsmld_attach_gsm().
b) Avoid calling gsm->receive in gsmld_receive_buf() if not initialized.

The current code might assume that gsm->receive is only called after MUX
activation. Therefore, variant a) may break the code in other places.
I see no need to initialize gsm->receive in gsm_activate_mux() and
gsmld_attach_gsm().

Best regards,
Daniel Starke
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Re: [PATCH] tty: n_gsm: fix missing assignment of gsm->receive() in gsmld_attach_gsm()

[Mazin Al Haddad]

On Wed Aug 10, 2022 at 12:08 PM +03, Starke, Daniel wrote:
> > 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.
>
> In my opinion there are only two possible ways to fix this:
> a) Move the gsm->receive initialization from gsm_activate_mux() to
> gsmld_attach_gsm().
> b) Avoid calling gsm->receive in gsmld_receive_buf() if not initialized.
>
> The current code might assume that gsm->receive is only called after MUX
> activation. Therefore, variant a) may break the code in other places.
> I see no need to initialize gsm->receive in gsm_activate_mux() and
> gsmld_attach_gsm().

Thanks for the feedback! I will send a v2 patch that implements a check
shortly. 

Re: [PATCH] tty: n_gsm: fix missing assignment of gsm->receive() in gsmld_attach_gsm()

[Mazin Al Haddad]

On Wed Aug 10, 2022 at 12:08 PM +03, Starke, Daniel wrote:
> > 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.
>
> In my opinion there are only two possible ways to fix this:
> a) Move the gsm->receive initialization from gsm_activate_mux() to
> gsmld_attach_gsm().
> b) Avoid calling gsm->receive in gsmld_receive_buf() if not initialized.
>
> The current code might assume that gsm->receive is only called after MUX
> activation. Therefore, variant a) may break the code in other places.
> I see no need to initialize gsm->receive in gsm_activate_mux() and
> gsmld_attach_gsm().

Thanks for the feedback! I will send a v2 patch that implements a check
shortly. 
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[PATCH] tty: n_gsm: fix missing assignment of gsm->receive() in gsmld_attach_gsm()

[Mazin Al Haddad]

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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[PATCH] tty: n_gsm: fix missing assignment of gsm->receive() in gsmld_attach_gsm()

[Mazin Al Haddad]

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

Re: [PATCH] tty: n_gsm: fix missing assignment of gsm->receive() in gsmld_attach_gsm()

[Greg KH]

On Wed, Aug 10, 2022 at 06:12:52AM +0300, Mazin Al Haddad wrote:
> Fixes a bug reported by syzbot.

I do not understand this sentence :(

> 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>

What commit does this fix?

thanks,

greg k-h

Re: [PATCH] tty: n_gsm: fix missing assignment of gsm->receive() in gsmld_attach_gsm()

[Greg KH]

On Wed, Aug 10, 2022 at 06:12:52AM +0300, Mazin Al Haddad wrote:
> Fixes a bug reported by syzbot.

I do not understand this sentence :(

> 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>

What commit does this fix?

thanks,

greg k-h
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