On 11/5/22 12:37 AM, David Howells wrote:
> netfslib has a number of places in which it performs iteration of an xarray
> whilst being under the RCU read lock. It *should* call xas_retry() as the
> first thing inside of the loop and do "continue" if it returns true in case
> the xarray walker passed out a special value indicating that the walk needs
> to be redone from the root[*].
>
> Fix this by adding the missing retry checks.
>
> [*] I wonder if this should be done inside xas_find(), xas_next_node() and
> suchlike, but I'm told that's not an simple change to effect.
>
> This can cause an oops like that below. Note the faulting address - this
> is an internal value (|0x2) returned from xarray.
>
> BUG: kernel NULL pointer dereference, address: 0000000000000402
> ...
> RIP: 0010:netfs_rreq_unlock+0xef/0x380 [netfs]
> ...
> Call Trace:
> netfs_rreq_assess+0xa6/0x240 [netfs]
> netfs_readpage+0x173/0x3b0 [netfs]
> ? init_wait_var_entry+0x50/0x50
> filemap_read_page+0x33/0xf0
> filemap_get_pages+0x2f2/0x3f0
> filemap_read+0xaa/0x320
> ? do_filp_open+0xb2/0x150
> ? rmqueue+0x3be/0xe10
> ceph_read_iter+0x1fe/0x680 [ceph]
> ? new_sync_read+0x115/0x1a0
> new_sync_read+0x115/0x1a0
> vfs_read+0xf3/0x180
> ksys_read+0x5f/0xe0
> do_syscall_64+0x38/0x90
> entry_SYSCALL_64_after_hwframe+0x44/0xae
>
> Fixes: 3d3c95046742 ("netfs: Provide readahead and readpage netfs helpers")
> Reported-by: George Law <glaw@xxxxxxxxxx>
> Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
> Reviewed-by: Jeff Layton <jlayton@xxxxxxxxxx>
> cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
> cc: linux-cachefs@xxxxxxxxxx
> cc: linux-fsdevel@xxxxxxxxxxxxxxx
> ---
Reviewed-by: Jingbo Xu <jefflexu@xxxxxxxxxxxxxxxxx>
--
Thanks,
Jingbo
