In the Linux kernel, the following vulnerability has been resolved:
tcp: Fix shift-out-of-bounds in dctcp_update_alpha().
In dctcp_update_alpha(), we use a module parameter dctcp_shift_g as follows:
alpha -= min_not_zero(alpha, alpha >> dctcp_shift_g); ... delivered_ce <<= (10 - dctcp_shift_g);
It seems syzkaller started fuzzing module parameters and triggered shift-out-of-bounds [0] by setting 100 to dctcp_shift_g:
memcpy((void*)0x20000080, "/sys/module/tcp_dctcp/parameters/dctcp_shift_g\000", 47); res = syscall(__NR_openat, /fd=/0xffffffffffffff9cul, /file=/0x20000080ul, /flags=/2ul, /mode=/0ul); memcpy((void*)0x20000000, "100\000", 4); syscall(__NR_write, /fd=/r[0], /val=/0x20000000ul, /len=/4ul);
Let's limit the max value of dctcp_shift_g by param_set_uint_minmax().
With this patch:
10
-bash: echo: write error: Invalid argument
[0]: UBSAN: shift-out-of-bounds in net/ipv4/tcp_dctcp.c:143:12 shift exponent 100 is too large for 32-bit type 'u32' (aka 'unsigned int') CPU: 0 PID: 8083 Comm: syz-executor345 Not tainted 6.9.0-05151-g1b294a1f3561 #2 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.13.0-1ubuntu1.1 04/01/2014 Call Trace: <TASK> __dump_stack lib/dump_stack.c:88 [inline] dump_stack_lvl+0x201/0x300 lib/dump_stack.c:114 ubsan_epilogue lib/ubsan.c:231 [inline] __ubsan_handle_shift_out_of_bounds+0x346/0x3a0 lib/ubsan.c:468 dctcp_update_alpha+0x540/0x570 net/ipv4/tcp_dctcp.c:143 tcp_in_ack_event net/ipv4/tcp_input.c:3802 [inline] tcp_ack+0x17b1/0x3bc0 net/ipv4/tcp_input.c:3948 tcp_rcv_state_process+0x57a/0x2290 net/ipv4/tcp_input.c:6711 tcp_v4_do_rcv+0x764/0xc40 net/ipv4/tcp_ipv4.c:1937 sk_backlog_rcv include/net/sock.h:1106 [inline] __release_sock+0x20f/0x350 net/core/sock.c:2983...