* [PATCH v2] tty: n_gsm: add sanity check for gsm->receive in gsm_receive_buf()
@ 2022-08-14 1:52 ` Mazin Al Haddad
0 siblings, 0 replies; 2+ messages in thread
From: Mazin Al Haddad @ 2022-08-14 1:52 UTC (permalink / raw)
To: gregkh
Cc: jirislaby, daniel.starke, linux-kernel, linux-kernel-mentees,
skhan, paskripkin, Mazin Al Haddad, syzbot+e3563f0c94e188366dbb
A null pointer dereference can happen when attempting to access the
"gsm->receive()" function in gsmld_receive_buf(). Currently, the code
assumes that gsm->recieve is only called after MUX activation.
Since the gsmld_receive_buf() function can be accessed without the need to
initialize the MUX, the gsm->receive() function will not be set and a
NULL pointer dereference will occur.
Fix this by avoiding the call to "gsm->receive()" in case the function is
not initialized by adding a sanity check.
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")
Link: https://syzkaller.appspot.com/bug?id=bdf035c61447f8c6e0e6920315d577cb5cc35ac5
Reported-and-tested-by: syzbot+e3563f0c94e188366dbb@syzkaller.appspotmail.com
Signed-off-by: Mazin Al Haddad <mazinalhaddad05@gmail.com>
---
v1->v2:
- Change commit title and description, removing unneeded and
unclear references to syzbot bug.
- Use a sanity check instead of reinitializing gsm->receive in
gsmld_attach_gsm()
drivers/tty/n_gsm.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c
index caa5c14ed57f..38688cb16c20 100644
--- a/drivers/tty/n_gsm.c
+++ b/drivers/tty/n_gsm.c
@@ -2858,7 +2858,8 @@ static void gsmld_receive_buf(struct tty_struct *tty, const unsigned char *cp,
flags = *fp++;
switch (flags) {
case TTY_NORMAL:
- gsm->receive(gsm, *cp);
+ if (gsm->receive)
+ gsm->receive(gsm, *cp);
break;
case TTY_OVERRUN:
case TTY_BREAK:
--
2.37.2
^ permalink raw reply related [flat|nested] 2+ messages in thread
* [PATCH v2] tty: n_gsm: add sanity check for gsm->receive in gsm_receive_buf()
@ 2022-08-14 1:52 ` Mazin Al Haddad
0 siblings, 0 replies; 2+ messages in thread
From: Mazin Al Haddad @ 2022-08-14 1:52 UTC (permalink / raw)
To: gregkh
Cc: daniel.starke, jirislaby, paskripkin,
syzbot+e3563f0c94e188366dbb, linux-kernel, linux-kernel-mentees,
Mazin Al Haddad
A null pointer dereference can happen when attempting to access the
"gsm->receive()" function in gsmld_receive_buf(). Currently, the code
assumes that gsm->recieve is only called after MUX activation.
Since the gsmld_receive_buf() function can be accessed without the need to
initialize the MUX, the gsm->receive() function will not be set and a
NULL pointer dereference will occur.
Fix this by avoiding the call to "gsm->receive()" in case the function is
not initialized by adding a sanity check.
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")
Link: https://syzkaller.appspot.com/bug?id=bdf035c61447f8c6e0e6920315d577cb5cc35ac5
Reported-and-tested-by: syzbot+e3563f0c94e188366dbb@syzkaller.appspotmail.com
Signed-off-by: Mazin Al Haddad <mazinalhaddad05@gmail.com>
---
v1->v2:
- Change commit title and description, removing unneeded and
unclear references to syzbot bug.
- Use a sanity check instead of reinitializing gsm->receive in
gsmld_attach_gsm()
drivers/tty/n_gsm.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c
index caa5c14ed57f..38688cb16c20 100644
--- a/drivers/tty/n_gsm.c
+++ b/drivers/tty/n_gsm.c
@@ -2858,7 +2858,8 @@ static void gsmld_receive_buf(struct tty_struct *tty, const unsigned char *cp,
flags = *fp++;
switch (flags) {
case TTY_NORMAL:
- gsm->receive(gsm, *cp);
+ if (gsm->receive)
+ gsm->receive(gsm, *cp);
break;
case TTY_OVERRUN:
case TTY_BREAK:
--
2.37.2
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2022-08-14 1:52 [PATCH v2] tty: n_gsm: add sanity check for gsm->receive in gsm_receive_buf() Mazin Al Haddad
2022-08-14 1:52 ` Mazin Al Haddad
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