CVE-2021-47237

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

net: hamradio: fix memory leak in mkiss_close

My local syzbot instance hit memory leak in mkiss_open()[1]. The problem was in missing free_netdev() in mkiss_close().

In mkiss_open() netdevice is allocated and then registered, but in mkiss_close() netdevice was only unregistered, but not freed.

Fail log:

BUG: memory leak unreferenced object 0xffff8880281ba000 (size 4096): comm syz-executor.1, pid 11443, jiffies 4295046091 (age 17.660s) hex dump (first 32 bytes): 61 78 30 00 00 00 00 00 00 00 00 00 00 00 00 00 ax0…………. 00 27 fa 2a 80 88 ff ff 00 00 00 00 00 00 00 00 ..*………… backtrace: [] kvmalloc_node+0x61/0xf0 [] alloc_netdev_mqs+0x98/0xe80 [] mkiss_open+0xb2/0x6f0 [1] [] tty_ldisc_open+0x9b/0x110 [] tty_set_ldisc+0x2e8/0x670 [] tty_ioctl+0xda3/0x1440 [] __x64_sys_ioctl+0x193/0x200 [] do_syscall_64+0x3a/0xb0 [] entry_SYSCALL_64_after_hwframe+0x44/0xae

BUG: memory leak unreferenced object 0xffff8880141a9a00 (size 96): comm syz-executor.1, pid 11443, jiffies 4295046091 (age 17.660s) hex dump (first 32 bytes): e8 a2 1b 28 80 88 ff ff e8 a2 1b 28 80 88 ff ff …(…….(…. 98 92 9c aa b0 40 02 00 00 00 00 00 00 00 00 00 …..@………. backtrace: [] __hw_addr_create_ex+0x5b/0x310 [] __hw_addr_add_ex+0x1f8/0x2b0 [] dev_addr_init+0x10b/0x1f0 [] alloc_netdev_mqs+0x13b/0xe80 [] mkiss_open+0xb2/0x6f0 [1] [] tty_ldisc_open+0x9b/0x110 [] tty_set_ldisc+0x2e8/0x670 [] tty_ioctl+0xda3/0x1440 [] __x64_sys_ioctl+0x193/0x200 [] do_syscall_64+0x3a/0xb0 [] entry_SYSCALL_64_after_hwframe+0x44/0xae

BUG: memory leak unreferenced object 0xffff8880219bfc00 (size 512): comm syz-executor.1, pid 11443, jiffies 4295046091 (age 17.660s) hex dump (first 32 bytes): 00 a0 1b 28 80 88 ff ff 80 8f b1 8d ff ff ff ff …(………… 80 8f b1 8d ff ff ff ff 00 00 00 00 00 00 00 00 ……………. backtrace: [] kvmalloc_node+0x61/0xf0 [] alloc_netdev_mqs+0x777/0xe80 [] mkiss_open+0xb2/0x6f0 [1] [] tty_ldisc_open+0x9b/0x110 [] tty_set_ldisc+0x2e8/0x670 [] tty_ioctl+0xda3/0x1440 [] __x64_sys_ioctl+0x193/0x200 [] do_syscall_64+0x3a/0xb0 [] entry_SYSCALL_64_after_hwframe+0x44/0xae

BUG: memory leak unreferenced object 0xffff888029b2b200 (size 256): comm syz-executor.1, pid 11443, jiffies 4295046091 (age 17.660s) hex dump (first 32 bytes): 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ……………. 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ……………. backtrace: [] kvmalloc_node+0x61/0xf0 [] alloc_netdev_mqs+0x912/0xe80 [] mkiss_open+0xb2/0x6f0 [1] [] tty_ldisc_open+0x9b/0x110 [] tty_set_ldisc+0x2e8/0x670 [] tty_ioctl+0xda3/0x1440 [] __x64_sys_ioctl+0x193/0x200 [] do_syscall_64+0x3a/0xb0 [] entry_SYSCALL_64_after_hwframe+0x44/0xae

Weakness

The product does not sufficiently track and release allocated memory after it has been used, which slowly consumes remaining memory.

Affected Software

Potential Mitigations

• Choose a language or tool that provides automatic memory management, or makes manual memory management less error-prone.
• For example, glibc in Linux provides protection against free of invalid pointers.
• When using Xcode to target OS X or iOS, enable automatic reference counting (ARC) [REF-391].
• To help correctly and consistently manage memory when programming in C++, consider using a smart pointer class such as std::auto_ptr (defined by ISO/IEC ISO/IEC 14882:2003), std::shared_ptr and std::unique_ptr (specified by an upcoming revision of the C++ standard, informally referred to as C++ 1x), or equivalent solutions such as Boost.

References

• https://git.kernel.org/stable/c/290b0b6432e2599021db0b8d6046f756d931c29f
• https://git.kernel.org/stable/c/3942d0f9ace1a95a74930b5b4fc0e5005c62b37b
• https://git.kernel.org/stable/c/765a8a04f828db7222b36a42b1031f576bfe95c3
• https://git.kernel.org/stable/c/7edcc682301492380fbdd604b4516af5ae667a13
• https://git.kernel.org/stable/c/a49cbb762ef20655f5c91abdc13658b0af5e159d
• https://git.kernel.org/stable/c/c16c4716a1b5ba4f83c7e00da457cba06761f119
• https://git.kernel.org/stable/c/c634ba0b4159838ff45a60d3a0ace3b4118077a5
• https://git.kernel.org/stable/c/f4de2b43d13b7cf3ced9310e371b90c836dbd7cd
• https://git.kernel.org/stable/c/290b0b6432e2599021db0b8d6046f756d931c29f
• https://git.kernel.org/stable/c/3942d0f9ace1a95a74930b5b4fc0e5005c62b37b
• https://git.kernel.org/stable/c/765a8a04f828db7222b36a42b1031f576bfe95c3
• https://git.kernel.org/stable/c/7edcc682301492380fbdd604b4516af5ae667a13
• https://git.kernel.org/stable/c/a49cbb762ef20655f5c91abdc13658b0af5e159d
• https://git.kernel.org/stable/c/c16c4716a1b5ba4f83c7e00da457cba06761f119
• https://git.kernel.org/stable/c/c634ba0b4159838ff45a60d3a0ace3b4118077a5
• https://git.kernel.org/stable/c/f4de2b43d13b7cf3ced9310e371b90c836dbd7cd