Commit 492888df authored by Jan Kara's avatar Jan Kara Committed by Theodore Ts'o
Browse files

ext4: fix data races when using cached status extents 



When using cached extent stored in extent status tree in tree->cache_es
another process holding ei->i_es_lock for reading can be racing with us
setting new value of tree->cache_es. If the compiler would decide to
refetch tree->cache_es at an unfortunate moment, it could result in a
bogus in_range() check. Fix the possible race by using READ_ONCE() when
using tree->cache_es only under ei->i_es_lock for reading.

Cc: stable@kernel.org
Reported-by: default avatar <syzbot+4a03518df1e31b537066@syzkaller.appspotmail.com>
Link: https://lore.kernel.org/all/000000000000d3b33905fa0fd4a6@google.com


Suggested-by: default avatarDmitry Vyukov <dvyukov@google.com>
Signed-off-by: default avatarJan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20230504125524.10802-1-jack@suse.cz


Signed-off-by: default avatarTheodore Ts'o <tytso@mit.edu>
parent 00d873c1

fs/ext4/extents_status.c

+13 −17
Original line number Diff line number Diff line
@@ -267,15 +267,13 @@ static void __es_find_extent_range(struct inode *inode, 


	/* see if the extent has been cached */

	es->es_lblk = es->es_len = es->es_pblk = 0;

	if (tree->cache_es) {

		es1 = tree->cache_es;

		if (in_range(lblk, es1->es_lblk, es1->es_len)) {

	es1 = READ_ONCE(tree->cache_es);

	if (es1 && in_range(lblk, es1->es_lblk, es1->es_len)) {

		es_debug("%u cached by [%u/%u) %llu %x\n",

			 lblk, es1->es_lblk, es1->es_len,

			 ext4_es_pblock(es1), ext4_es_status(es1));

		goto out;

	}

	}



	es1 = __es_tree_search(&tree->root, lblk);
@@ -293,7 +291,7 @@ static void __es_find_extent_range(struct inode *inode, 
	}



	if (es1 && matching_fn(es1)) {

		tree->cache_es = es1;

		WRITE_ONCE(tree->cache_es, es1);

		es->es_lblk = es1->es_lblk;

		es->es_len = es1->es_len;

		es->es_pblk = es1->es_pblk;
@@ -931,15 +929,13 @@ int ext4_es_lookup_extent(struct inode *inode, ext4_lblk_t lblk, 


	/* find extent in cache firstly */

	es->es_lblk = es->es_len = es->es_pblk = 0;

	if (tree->cache_es) {

		es1 = tree->cache_es;

		if (in_range(lblk, es1->es_lblk, es1->es_len)) {

	es1 = READ_ONCE(tree->cache_es);

	if (es1 && in_range(lblk, es1->es_lblk, es1->es_len)) {

		es_debug("%u cached by [%u/%u)\n",

			 lblk, es1->es_lblk, es1->es_len);

		found = 1;

		goto out;

	}

	}



	node = tree->root.rb_node;

	while (node) {