diff options
| author | Jan Kara <jack@suse.cz> | 2023-05-04 14:55:24 +0200 |
|---|---|---|
| committer | Theodore Ts'o <tytso@mit.edu> | 2023-05-13 18:05:04 -0400 |
| commit | 492888df0c7b42fc0843631168b0021bc4caee84 (patch) | |
| tree | dc11ae138e5738d0b5e9e471b650ad5ad71b80d7 /fs | |
| parent | 00d873c17e29cc32d90ca852b82685f1673acaa5 (diff) | |
| download | lwn-492888df0c7b42fc0843631168b0021bc4caee84.tar.gz lwn-492888df0c7b42fc0843631168b0021bc4caee84.zip | |
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: 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>
Diffstat (limited to 'fs')
| -rw-r--r-- | fs/ext4/extents_status.c | 30 |
1 files changed, 13 insertions, 17 deletions
diff --git a/fs/ext4/extents_status.c b/fs/ext4/extents_status.c index 7bc221038c6c..595abb9e7d74 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 @@ out: } 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; |