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authorJan Kara <jack@suse.cz>2022-07-12 12:54:24 +0200
committerTheodore Ts'o <tytso@mit.edu>2022-08-02 23:56:25 -0400
commit65f8b80053a1b2fd602daa6814e62d6fa90e5e9b (patch)
tree36ddb4b80cdd40aee91afa36bfebd2d0dac89d68
parentfd48e9acdf26d0cbd80051de07d4a735d05d29b2 (diff)
ext4: fix race when reusing xattr blocks
When ext4_xattr_block_set() decides to remove xattr block the following race can happen: CPU1 CPU2 ext4_xattr_block_set() ext4_xattr_release_block() new_bh = ext4_xattr_block_cache_find() lock_buffer(bh); ref = le32_to_cpu(BHDR(bh)->h_refcount); if (ref == 1) { ... mb_cache_entry_delete(); unlock_buffer(bh); ext4_free_blocks(); ... ext4_forget(..., bh, ...); jbd2_journal_revoke(..., bh); ext4_journal_get_write_access(..., new_bh, ...) do_get_write_access() jbd2_journal_cancel_revoke(..., new_bh); Later the code in ext4_xattr_block_set() finds out the block got freed and cancels reusal of the block but the revoke stays canceled and so in case of block reuse and journal replay the filesystem can get corrupted. If the race works out slightly differently, we can also hit assertions in the jbd2 code. Fix the problem by making sure that once matching mbcache entry is found, code dropping the last xattr block reference (or trying to modify xattr block in place) waits until the mbcache entry reference is dropped. This way code trying to reuse xattr block is protected from someone trying to drop the last reference to xattr block. Reported-and-tested-by: Ritesh Harjani <ritesh.list@gmail.com> CC: stable@vger.kernel.org Fixes: 82939d7999df ("ext4: convert to mbcache2") Signed-off-by: Jan Kara <jack@suse.cz> Link: https://lore.kernel.org/r/20220712105436.32204-5-jack@suse.cz Signed-off-by: Theodore Ts'o <tytso@mit.edu>
-rw-r--r--fs/ext4/xattr.c67
1 files changed, 45 insertions, 22 deletions
diff --git a/fs/ext4/xattr.c b/fs/ext4/xattr.c
index a25942a74929..533216e80fa2 100644
--- a/fs/ext4/xattr.c
+++ b/fs/ext4/xattr.c
@@ -439,9 +439,16 @@ error:
/* Remove entry from mbcache when EA inode is getting evicted */
void ext4_evict_ea_inode(struct inode *inode)
{
- if (EA_INODE_CACHE(inode))
- mb_cache_entry_delete(EA_INODE_CACHE(inode),
- ext4_xattr_inode_get_hash(inode), inode->i_ino);
+ struct mb_cache_entry *oe;
+
+ if (!EA_INODE_CACHE(inode))
+ return;
+ /* Wait for entry to get unused so that we can remove it */
+ while ((oe = mb_cache_entry_delete_or_get(EA_INODE_CACHE(inode),
+ ext4_xattr_inode_get_hash(inode), inode->i_ino))) {
+ mb_cache_entry_wait_unused(oe);
+ mb_cache_entry_put(EA_INODE_CACHE(inode), oe);
+ }
}
static int
@@ -1229,6 +1236,7 @@ ext4_xattr_release_block(handle_t *handle, struct inode *inode,
if (error)
goto out;
+retry_ref:
lock_buffer(bh);
hash = le32_to_cpu(BHDR(bh)->h_hash);
ref = le32_to_cpu(BHDR(bh)->h_refcount);
@@ -1238,9 +1246,18 @@ ext4_xattr_release_block(handle_t *handle, struct inode *inode,
* This must happen under buffer lock for
* ext4_xattr_block_set() to reliably detect freed block
*/
- if (ea_block_cache)
- mb_cache_entry_delete(ea_block_cache, hash,
- bh->b_blocknr);
+ if (ea_block_cache) {
+ struct mb_cache_entry *oe;
+
+ oe = mb_cache_entry_delete_or_get(ea_block_cache, hash,
+ bh->b_blocknr);
+ if (oe) {
+ unlock_buffer(bh);
+ mb_cache_entry_wait_unused(oe);
+ mb_cache_entry_put(ea_block_cache, oe);
+ goto retry_ref;
+ }
+ }
get_bh(bh);
unlock_buffer(bh);
@@ -1867,9 +1884,20 @@ ext4_xattr_block_set(handle_t *handle, struct inode *inode,
* ext4_xattr_block_set() to reliably detect modified
* block
*/
- if (ea_block_cache)
- mb_cache_entry_delete(ea_block_cache, hash,
- bs->bh->b_blocknr);
+ if (ea_block_cache) {
+ struct mb_cache_entry *oe;
+
+ oe = mb_cache_entry_delete_or_get(ea_block_cache,
+ hash, bs->bh->b_blocknr);
+ if (oe) {
+ /*
+ * Xattr block is getting reused. Leave
+ * it alone.
+ */
+ mb_cache_entry_put(ea_block_cache, oe);
+ goto clone_block;
+ }
+ }
ea_bdebug(bs->bh, "modifying in-place");
error = ext4_xattr_set_entry(i, s, handle, inode,
true /* is_block */);
@@ -1885,6 +1913,7 @@ ext4_xattr_block_set(handle_t *handle, struct inode *inode,
goto cleanup;
goto inserted;
}
+clone_block:
unlock_buffer(bs->bh);
ea_bdebug(bs->bh, "cloning");
s->base = kmemdup(BHDR(bs->bh), bs->bh->b_size, GFP_NOFS);
@@ -1990,18 +2019,13 @@ inserted:
lock_buffer(new_bh);
/*
* We have to be careful about races with
- * freeing, rehashing or adding references to
- * xattr block. Once we hold buffer lock xattr
- * block's state is stable so we can check
- * whether the block got freed / rehashed or
- * not. Since we unhash mbcache entry under
- * buffer lock when freeing / rehashing xattr
- * block, checking whether entry is still
- * hashed is reliable. Same rules hold for
- * e_reusable handling.
+ * adding references to xattr block. Once we
+ * hold buffer lock xattr block's state is
+ * stable so we can check the additional
+ * reference fits.
*/
- if (hlist_bl_unhashed(&ce->e_hash_list) ||
- !ce->e_reusable) {
+ ref = le32_to_cpu(BHDR(new_bh)->h_refcount) + 1;
+ if (ref > EXT4_XATTR_REFCOUNT_MAX) {
/*
* Undo everything and check mbcache
* again.
@@ -2016,9 +2040,8 @@ inserted:
new_bh = NULL;
goto inserted;
}
- ref = le32_to_cpu(BHDR(new_bh)->h_refcount) + 1;
BHDR(new_bh)->h_refcount = cpu_to_le32(ref);
- if (ref >= EXT4_XATTR_REFCOUNT_MAX)
+ if (ref == EXT4_XATTR_REFCOUNT_MAX)
ce->e_reusable = 0;
ea_bdebug(new_bh, "reusing; refcount now=%d",
ref);