From 48a8d01a97178f735e0957b580a598e00c5c6ced Mon Sep 17 00:00:00 2001 From: Filipe Manana Date: Fri, 12 Oct 2018 13:02:48 +0100 Subject: [PATCH] Btrfs: fix use-after-free during inode eviction BugLink: http://bugs.launchpad.net/bugs/1810820 commit 421f0922a2cfb0c75acd9746454aaa576c711a65 upstream. At inode.c:evict_inode_truncate_pages(), when we iterate over the inode's extent states, we access an extent state record's "state" field after we unlocked the inode's io tree lock. This can lead to a use-after-free issue because after we unlock the io tree that extent state record might have been freed due to being merged into another adjacent extent state record (a previous inflight bio for a read operation finished in the meanwhile which unlocked a range in the io tree and cause a merge of extent state records, as explained in the comment before the while loop added in commit 6ca0709756710 ("Btrfs: fix hang during inode eviction due to concurrent readahead")). Fix this by keeping a copy of the extent state's flags in a local variable and using it after unlocking the io tree. Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=201189 Fixes: b9d0b38928e2 ("btrfs: Add handler for invalidate page") CC: stable@vger.kernel.org # 4.4+ Reviewed-by: Qu Wenruo Signed-off-by: Filipe Manana Reviewed-by: David Sterba Signed-off-by: David Sterba Signed-off-by: Greg Kroah-Hartman Signed-off-by: Kamal Mostafa Signed-off-by: Kleber Sacilotto de Souza --- fs/btrfs/inode.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c index 50cd0118bcd2aa..dc0f9d089b1931 100644 --- a/fs/btrfs/inode.c +++ b/fs/btrfs/inode.c @@ -5302,11 +5302,13 @@ static void evict_inode_truncate_pages(struct inode *inode) struct extent_state *cached_state = NULL; u64 start; u64 end; + unsigned state_flags; node = rb_first(&io_tree->state); state = rb_entry(node, struct extent_state, rb_node); start = state->start; end = state->end; + state_flags = state->state; spin_unlock(&io_tree->lock); lock_extent_bits(io_tree, start, end, &cached_state); @@ -5319,7 +5321,7 @@ static void evict_inode_truncate_pages(struct inode *inode) * * Note, end is the bytenr of last byte, so we need + 1 here. */ - if (state->state & EXTENT_DELALLOC) + if (state_flags & EXTENT_DELALLOC) btrfs_qgroup_free_data(inode, NULL, start, end - start + 1); clear_extent_bit(io_tree, start, end,