bpf, sockmap: fix integer overflow in bpf_msg_pop_data() bounds check

Overview

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

bpf, sockmap: fix integer overflow in bpf_msg_pop_data() bounds check

start and len are u32, so

u64 last = start + len;

evaluates start + len in 32-bit and wraps before storing it in last. The bounds check

if (start >= offset + l || last > msg->sg.size)
	return -EINVAL;

can then be passed with an out-of-range start/len, after which the pop loop runs off the end of the scatterlist and sk_msg_shift_left() calls put_page() on the empty msg->sg.end slot:

Oops: general protection fault, probably for non-canonical address 0xdffffc0000000001: 0000 [#1] SMP KASAN PTI KASAN: null-ptr-deref in range [0x0000000000000008-0x000000000000000f] RIP: 0010:sk_msg_shift_left net/core/filter.c:2957 [inline] RIP: 0010:____bpf_msg_pop_data net/core/filter.c:3103 [inline] RIP: 0010:bpf_msg_pop_data+0x753/0x1a10 net/core/filter.c:2984 Call Trace: <TASK> bpf_prog_4cc92c278f4d5d56+0x1b1/0x1e8 bpf_prog_run_pin_on_cpu+0x107/0x320 include/linux/filter.h:746 sk_psock_msg_verdict+0x357/0x7f0 net/core/skmsg.c:934 tcp_bpf_send_verdict net/ipv4/tcp_bpf.c:420 [inline] tcp_bpf_sendmsg+0x766/0x1ae0 net/ipv4/tcp_bpf.c:583 __sock_sendmsg+0x153/0x1c0 net/socket.c:802 __sys_sendto+0x326/0x430 net/socket.c:2265 __x64_sys_sendto+0xe3/0x100 net/socket.c:2268 do_syscall_64+0x14c/0x480 entry_SYSCALL_64_after_hwframe+0x77/0x7f </TASK>

Widen the addition with a (u64) cast so the bound is evaluated in 64-bit and a len near U32_MAX no longer wraps below msg->sg.size.

While here, change pop from int to u32. It counts bytes against the unsigned scatterlist lengths and can never be negative, so the signed type only invites sign-confusion in the pop loop.

Affected

• Linux >= 7246d8ed4dcce23f7509949a77be15fa9f0e3d28 < 9ef44ed6fb0c1db01cfcc3de432a33e719713eb5
• Linux >= 7246d8ed4dcce23f7509949a77be15fa9f0e3d28 < d693c5ed67dabe1ccbf8dcea93075bdc9ffd4ca0
• Linux >= 7246d8ed4dcce23f7509949a77be15fa9f0e3d28 < ba5cc05dae8fce237d191c7ea96b1107a791e548
• Linux >= 7246d8ed4dcce23f7509949a77be15fa9f0e3d28 < c05a0ec1cdced622a1a0c7d85679fe02f31033ec
• Linux >= 7246d8ed4dcce23f7509949a77be15fa9f0e3d28 < 17eb9832a10db2f7a80cb429ca2bc5038445a943
• Linux >= 7246d8ed4dcce23f7509949a77be15fa9f0e3d28 < fe09dd288722f1c749b7506c0b3e7841a7d85027
• Linux >= 7246d8ed4dcce23f7509949a77be15fa9f0e3d28 < e09f7bd7273928b4089e6b71f8e992f2b356ca1b
• Linux >= 7246d8ed4dcce23f7509949a77be15fa9f0e3d28 < a48802fb2cd2d1e23651989f8ff4d15e9d5dad54
• Linux 5.0

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.