From: David Howells dhowells@redhat.com
[ Upstream commit 7e043a80b5dae5c2d2cf84031501de7827fd6c00 ]
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
Changes: ======== ver #2) - Changed an unsigned int to a size_t to reduce the likelihood of an overflow as per Willy's suggestion. - Added an additional patch to fix the maths.
Fixes: 3d3c95046742 ("netfs: Provide readahead and readpage netfs helpers") Reported-by: George Law glaw@redhat.com Signed-off-by: David Howells dhowells@redhat.com Reviewed-by: Jeff Layton jlayton@kernel.org Reviewed-by: Jingbo Xu jefflexu@linux.alibaba.com cc: Matthew Wilcox willy@infradead.org cc: linux-cachefs@redhat.com cc: linux-fsdevel@vger.kernel.org Link: https://lore.kernel.org/r/166749229733.107206.17482609105741691452.stgit@war... # v1 Link: https://lore.kernel.org/r/166757987929.950645.12595273010425381286.stgit@war... # v2 Signed-off-by: Sasha Levin sashal@kernel.org --- fs/netfs/buffered_read.c | 9 +++++++-- fs/netfs/io.c | 3 +++ 2 files changed, 10 insertions(+), 2 deletions(-)
diff --git a/fs/netfs/buffered_read.c b/fs/netfs/buffered_read.c index 0ce535852151..baf668fb4315 100644 --- a/fs/netfs/buffered_read.c +++ b/fs/netfs/buffered_read.c @@ -46,10 +46,15 @@ void netfs_rreq_unlock_folios(struct netfs_io_request *rreq)
rcu_read_lock(); xas_for_each(&xas, folio, last_page) { - unsigned int pgpos = (folio_index(folio) - start_page) * PAGE_SIZE; - unsigned int pgend = pgpos + folio_size(folio); + unsigned int pgpos, pgend; bool pg_failed = false;
+ if (xas_retry(&xas, folio)) + continue; + + pgpos = (folio_index(folio) - start_page) * PAGE_SIZE; + pgend = pgpos + folio_size(folio); + for (;;) { if (!subreq) { pg_failed = true; diff --git a/fs/netfs/io.c b/fs/netfs/io.c index 428925899282..e374767d1b68 100644 --- a/fs/netfs/io.c +++ b/fs/netfs/io.c @@ -121,6 +121,9 @@ static void netfs_rreq_unmark_after_write(struct netfs_io_request *rreq, XA_STATE(xas, &rreq->mapping->i_pages, subreq->start / PAGE_SIZE);
xas_for_each(&xas, folio, (subreq->start + subreq->len - 1) / PAGE_SIZE) { + if (xas_retry(&xas, folio)) + continue; + /* We might have multiple writes from the same huge * folio, but we mustn't unlock a folio more than once. */