From: Filipe Manana fdmanana@suse.com
mainline inclusion from mainline-v6.13-rc5 commit 44f52bbe96dfdbe4aca3818a2534520082a07040 category: bugfix bugzilla: https://gitee.com/src-openeuler/kernel/issues/IBG2PK CVE: CVE-2024-56759
Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i...
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When a COWing a tree block, at btrfs_cow_block(), and we have the tracepoint trace_btrfs_cow_block() enabled and preemption is also enabled (CONFIG_PREEMPT=y), we can trigger a use-after-free in the COWed extent buffer while inside the tracepoint code. This is because in some paths that call btrfs_cow_block(), such as btrfs_search_slot(), we are holding the last reference on the extent buffer @buf so btrfs_force_cow_block() drops the last reference on the @buf extent buffer when it calls free_extent_buffer_stale(buf), which schedules the release of the extent buffer with RCU. This means that if we are on a kernel with preemption, the current task may be preempted before calling trace_btrfs_cow_block() and the extent buffer already released by the time trace_btrfs_cow_block() is called, resulting in a use-after-free.
Fix this by moving the trace_btrfs_cow_block() from btrfs_cow_block() to btrfs_force_cow_block() before the COWed extent buffer is freed. This also has a side effect of invoking the tracepoint in the tree defrag code, at defrag.c:btrfs_realloc_node(), since btrfs_force_cow_block() is called there, but this is fine and it was actually missing there.
Reported-by: syzbot+8517da8635307182c8a5@syzkaller.appspotmail.com Link: https://lore.kernel.org/linux-btrfs/6759a9b9.050a0220.1ac542.000d.GAE@google... CC: stable@vger.kernel.org # 5.4+ Reviewed-by: Qu Wenruo wqu@suse.com Signed-off-by: Filipe Manana fdmanana@suse.com Signed-off-by: David Sterba dsterba@suse.com Conflicts: fs/btrfs/ctree.c [__btrfs_cow_block did not rename to btrfs_force_cow_block yet.] Signed-off-by: Yifan Qiao qiaoyifan4@huawei.com --- fs/btrfs/ctree.c | 9 +++------ 1 file changed, 3 insertions(+), 6 deletions(-)
diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c index 2eb4e03080ac..ddcc22384e36 100644 --- a/fs/btrfs/ctree.c +++ b/fs/btrfs/ctree.c @@ -648,6 +648,8 @@ static noinline int __btrfs_cow_block(struct btrfs_trans_handle *trans, btrfs_free_tree_block(trans, btrfs_root_id(root), buf, parent_start, last_ref); } + + trace_btrfs_cow_block(root, buf, cow); if (unlock_orig) btrfs_tree_unlock(buf); free_extent_buffer_stale(buf); @@ -699,7 +701,6 @@ noinline int btrfs_cow_block(struct btrfs_trans_handle *trans, { struct btrfs_fs_info *fs_info = root->fs_info; u64 search_start; - int ret;
if (unlikely(test_bit(BTRFS_ROOT_DELETING, &root->state))) { btrfs_abort_transaction(trans, -EUCLEAN); @@ -740,12 +741,8 @@ noinline int btrfs_cow_block(struct btrfs_trans_handle *trans, * Also We don't care about the error, as it's handled internally. */ btrfs_qgroup_trace_subtree_after_cow(trans, root, buf); - ret = __btrfs_cow_block(trans, root, buf, parent, + return __btrfs_cow_block(trans, root, buf, parent, parent_slot, cow_ret, search_start, 0, nest); - - trace_btrfs_cow_block(root, buf, *cow_ret); - - return ret; } ALLOW_ERROR_INJECTION(btrfs_cow_block, ERRNO);