CVE-2022-49940

In the Linux kernel, the following vulnerability has been resolved:

tty: ngsm: add sanity check for gsm->receive in gsmreceive_buf()

A null pointer dereference can happen when attempting to access the "gsm->receive()" function in gsmldreceivebuf(). Currently, the code assumes that gsm->recieve is only called after MUX activation. Since the gsmldreceivebuf() 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> gsmldreceivebuf+0x1c2/0x2f0 drivers/tty/ngsm.c:2861 tiocsti drivers/tty/ttyio.c:2293 [inline] ttyioctl+0xa75/0x15d0 drivers/tty/ttyio.c:2692 vfs_ioctl fs/ioctl.c:51 [inline] __dosysioctl fs/ioctl.c:870 [inline] __sesysioctl fs/ioctl.c:856 [inline] __x64sysioctl+0x193/0x200 fs/ioctl.c:856 dosyscallx64 arch/x86/entry/common.c:50 [inline] dosyscall64+0x35/0xb0 arch/x86/entry/common.c:80 entrySYSCALL64afterhwframe+0x63/0xcd