From: Jan Kara <jack@suse.cz>
Date: Thu, 4 May 2023 14:55:24 +0200
Subject: [PATCH] ext4: fix data races when using cached status extents
References: bsc#1012628
Patch-mainline: 6.3.3
Git-commit: 492888df0c7b42fc0843631168b0021bc4caee84
commit 492888df0c7b42fc0843631168b0021bc4caee84 upstream.
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: syzbot+4a03518df1e31b537066@syzkaller.appspotmail.com
Link: https://lore.kernel.org/all/000000000000d3b33905fa0fd4a6@google.com
Suggested-by: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20230504125524.10802-1-jack@suse.cz
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
---
fs/ext4/extents_status.c | 30 +++++++++++++-----------------
1 file changed, 13 insertions(+), 17 deletions(-)
diff --git a/fs/ext4/extents_status.c b/fs/ext4/extents_status.c
index 7bc22103..595abb9e 100644
--- a/fs/ext4/extents_status.c
+++ b/fs/ext4/extents_status.c
@@ -267,14 +267,12 @@ 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)) {
- 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 = 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;
@@ -931,14 +929,12 @@ 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)) {
- es_debug("%u cached by [%u/%u)\n",
- lblk, es1->es_lblk, es1->es_len);
- found = 1;
- goto out;
- }
+ 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;
--
2.35.3