Re: [PATCH] net/rds: restrict iovecs length for RDS_CMSG_RDMA_ARGS

On Feb 1, 2021, at 12:32 PM, Sabyrzhan Tasbolatov [off-list ref] wrote:

syzbot found WARNING in rds_rdma_extra_size [1] when RDS_CMSG_RDMA_ARGS
control message is passed with user-controlled
0x40001 bytes of args->nr_local, causing order >= MAX_ORDER condition.

The exact value 0x40001 can be checked with UIO_MAXIOV which is 0x400.
So for kcalloc() 0x400 iovecs with sizeof(struct rds_iovec) = 0x10
is the closest limit, with 0x10 leftover.

Same condition is currently done in rds_cmsg_rdma_args().

[1] WARNING: mm/page_alloc.c:5011
[..]
Call Trace:
alloc_pages_current+0x18c/0x2a0 mm/mempolicy.c:2267
alloc_pages include/linux/gfp.h:547 [inline]
kmalloc_order+0x2e/0xb0 mm/slab_common.c:837
kmalloc_order_trace+0x14/0x120 mm/slab_common.c:853
kmalloc_array include/linux/slab.h:592 [inline]
kcalloc include/linux/slab.h:621 [inline]
rds_rdma_extra_size+0xb2/0x3b0 net/rds/rdma.c:568
rds_rm_size net/rds/send.c:928 [inline]

Reported-by: syzbot+1bd2b07f93745fa38425@syzkaller.appspotmail.com
Signed-off-by: Sabyrzhan Tasbolatov <redacted>
—

Looks fine by me.
Acked-by: Santosh Shilimkar <redacted>