Subject: Re: [PATCH] net/rds: Fix UBSAN: array-index-out-of-bounds in rds_cmsg_recv

From: Simon Horman <[email-masked]>
Date: Sat, 20 Jan 2024 11:48:56 +0000

On Fri, Jan 19, 2024 at 05:48:39PM -0800, Sharath Srinivasan wrote:
> Syzcaller UBSAN crash occurs in rds_cmsg_recv(),
> which reads inc->i_rx_lat_trace[j + 1] with index 4 (3 + 1),
> but with array size of 4 (RDS_RX_MAX_TRACES).
> Here 'j' is assigned from rs->rs_rx_trace[i] and in-turn from
> trace.rx_trace_pos[i] in rds_recv_track_latency(),
> with both arrays sized 3 (RDS_MSG_RX_DGRAM_TRACE_MAX). So fix the
> off-by-one bounds check in rds_recv_track_latency() to prevent
> a potential crash in rds_cmsg_recv().
> 
> Found by syzcaller:
> =================================================================
> UBSAN: array-index-out-of-bounds in net/rds/recv.c:585:39
> index 4 is out of range for type 'u64 [4]'
> CPU: 1 PID: 8058 Comm: syz-executor228 Not tainted 6.6.0-gd2f51b3516da #1
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996),
> BIOS 1.15.0-1 04/01/2014
> Call Trace:
>  <TASK>
>  __dump_stack lib/dump_stack.c:88 [inline]
>  dump_stack_lvl+0x136/0x150 lib/dump_stack.c:106
>  ubsan_epilogue lib/ubsan.c:217 [inline]
>  __ubsan_handle_out_of_bounds+0xd5/0x130 lib/ubsan.c:348
>  rds_cmsg_recv+0x60d/0x700 net/rds/recv.c:585
>  rds_recvmsg+0x3fb/0x1610 net/rds/recv.c:716
>  sock_recvmsg_nosec net/socket.c:1044 [inline]
>  sock_recvmsg+0xe2/0x160 net/socket.c:1066
>  __sys_recvfrom+0x1b6/0x2f0 net/socket.c:2246
>  __do_sys_recvfrom net/socket.c:2264 [inline]
>  __se_sys_recvfrom net/socket.c:2260 [inline]
>  __x64_sys_recvfrom+0xe0/0x1b0 net/socket.c:2260
>  do_syscall_x64 arch/x86/entry/common.c:51 [inline]
>  do_syscall_64+0x40/0x110 arch/x86/entry/common.c:82
>  entry_SYSCALL_64_after_hwframe+0x63/0x6b
> ==================================================================
> 
> Fixes: 3289025aedc0 ("RDS: add receive message trace used by application")
> Reported-by: Chenyuan Yang <[email-masked]>
> Closes: https://lore.kernel.org/linux-rdma/[email-masked]/
> Signed-off-by: Sharath Srinivasan <[email-masked]>

Thanks,

looking over the code in question I agree with your analysis, that the
problem was introduced in the cited commit, and that this is an appropriate
fix.

Reviewed-by: Simon Horman <[email-masked]>