CVE-2022-48839

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

net/packet: fix slab-out-of-bounds access in packet_recvmsg()

syzbot found that when an AF_PACKET socket is using PACKET_COPY_THRESH and mmap operations, tpacket_rcv() is queueing skbs with garbage in skb->cb[], triggering a too big copy [1]

Presumably, users of af_packet using mmap() already gets correct metadata from the mapped buffer, we can simply make sure to clear 12 bytes that might be copied to user space later.

BUG: KASAN: stack-out-of-bounds in memcpy include/linux/fortify-string.h:225 [inline] BUG: KASAN: stack-out-of-bounds in packet_recvmsg+0x56c/0x1150 net/packet/af_packet.c:3489 Write of size 165 at addr ffffc9000385fb78 by task syz-executor233/3631

CPU: 0 PID: 3631 Comm: syz-executor233 Not tainted 5.17.0-rc7-syzkaller-02396-g0b3660695e80 #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 Call Trace: __dump_stack lib/dump_stack.c:88 [inline] dump_stack_lvl+0xcd/0x134 lib/dump_stack.c:106 print_address_description.constprop.0.cold+0xf/0x336 mm/kasan/report.c:255 __kasan_report mm/kasan/report.c:442 [inline] kasan_report.cold+0x83/0xdf mm/kasan/report.c:459 check_region_inline mm/kasan/generic.c:183 [inline] kasan_check_range+0x13d/0x180 mm/kasan/generic.c:189 memcpy+0x39/0x60 mm/kasan/shadow.c:66 memcpy include/linux/fortify-string.h:225 [inline] packet_recvmsg+0x56c/0x1150 net/packet/af_packet.c:3489 sock_recvmsg_nosec net/socket.c:948 [inline] sock_recvmsg net/socket.c:966 [inline] sock_recvmsg net/socket.c:962 [inline] ____sys_recvmsg+0x2c4/0x600 net/socket.c:2632 ___sys_recvmsg+0x127/0x200 net/socket.c:2674 __sys_recvmsg+0xe2/0x1a0 net/socket.c:2704 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+0x44/0xae RIP: 0033:0x7fdfd5954c29 Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 41 15 00 00 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 c0 ff ff ff f7 d8 64 89 01 48 RSP: 002b:00007ffcf8e71e48 EFLAGS: 00000246 ORIG_RAX: 000000000000002f RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 00007fdfd5954c29 RDX: 0000000000000000 RSI: 0000000020000500 RDI: 0000000000000005 RBP: 0000000000000000 R08: 000000000000000d R09: 000000000000000d R10: 0000000000000000 R11: 0000000000000246 R12: 00007ffcf8e71e60 R13: 00000000000f4240 R14: 000000000000c1ff R15: 00007ffcf8e71e54

addr ffffc9000385fb78 is located in stack of task syz-executor233/3631 at offset 32 in frame: ____sys_recvmsg+0x0/0x600 include/linux/uio.h:246

this frame has 1 object: [32, 160) addr

Memory state around the buggy address: ffffc9000385fa80: 00 04 f3 f3 f3 f3 f3 00 00 00 00 00 00 00 00 00 ffffc9000385fb00: 00 00 00 00 00 00 00 00 00 00 00 f1 f1 f1 f1 00

ffffc9000385fb80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 f3 ^ ffffc9000385fc00: f3 f3 f3 00 00 00 00 00 00 00 00 00 00 00 00 f1 ffffc9000385fc80: f1 f1 f1 00 f2 f2 f2 00 f2 f2 f2 00 00 00 00 00 ==================================================================

Weakness

The product reads data past the end, or before the beginning, of the intended buffer.

Affected Software

Potential Mitigations

• Assume all input is malicious. Use an “accept known good” input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does.
• When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and conformance to business rules. As an example of business rule logic, “boat” may be syntactically valid because it only contains alphanumeric characters, but it is not valid if the input is only expected to contain colors such as “red” or “blue.”
• Do not rely exclusively on looking for malicious or malformed inputs. This is likely to miss at least one undesirable input, especially if the code’s environment changes. This can give attackers enough room to bypass the intended validation. However, denylists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright.
• To reduce the likelihood of introducing an out-of-bounds read, ensure that you validate and ensure correct calculations for any length argument, buffer size calculation, or offset. Be especially careful of relying on a sentinel (i.e. special character such as NUL) in untrusted inputs.

Related Attack Patterns

• https://cwe.mitre.org/data/definitions/540.html

References

• https://git.kernel.org/stable/c/268dcf1f7b3193bc446ec3d14e08a240e9561e4d
• https://git.kernel.org/stable/c/70b7b3c055fd4a464da8da55ff4c1f84269f9b02
• https://git.kernel.org/stable/c/a055f5f2841f7522b44a2b1eccb1951b4b03d51a
• https://git.kernel.org/stable/c/a33dd1e6693f80d805155b3f69c18c2f642915da
• https://git.kernel.org/stable/c/b1e27cda1e3c12b705875bb7e247a97168580e33
• https://git.kernel.org/stable/c/b9d5772d60f8e7ef34e290f72fc20e3a4883e7d0
• https://git.kernel.org/stable/c/c700525fcc06b05adfea78039de02628af79e07a
• https://git.kernel.org/stable/c/ef591b35176029fdefea38e8388ffa371e18f4b2