| Message ID | 1b96eb7eb9ce220acc21b2ac2057a5a3eab1fb3b.1733953828.git.fdmanana@suse.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | [v2] btrfs: fix use-after-free when COWing tree bock and tracing is enabled | expand |
在 2024/12/12 08:23, fdmanana@kernel.org 写道: > From: Filipe Manana <fdmanana@suse.com> > > 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.com/ > Signed-off-by: Filipe Manana <fdmanana@suse.com> Reviewed-by: Qu Wenruo <wqu@suse.com> Thanks for pinning down and fix the bug, Qu > --- > > V2: Instead of temporarily bumping the extent buffer's reference count > to safely call the tracepoint, move the tracepoint call to > btrfs_force_cow_block(). > > fs/btrfs/ctree.c | 11 ++++------- > 1 file changed, 4 insertions(+), 7 deletions(-) > > diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c > index 693dc27ffb89..185985a337b3 100644 > --- a/fs/btrfs/ctree.c > +++ b/fs/btrfs/ctree.c > @@ -654,6 +654,8 @@ int btrfs_force_cow_block(struct btrfs_trans_handle *trans, > goto error_unlock_cow; > } > } > + > + trace_btrfs_cow_block(root, buf, cow); > if (unlock_orig) > btrfs_tree_unlock(buf); > free_extent_buffer_stale(buf); > @@ -710,7 +712,6 @@ 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); > @@ -751,12 +752,8 @@ 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_force_cow_block(trans, root, buf, parent, parent_slot, > - cow_ret, search_start, 0, nest); > - > - trace_btrfs_cow_block(root, buf, *cow_ret); > - > - return ret; > + return btrfs_force_cow_block(trans, root, buf, parent, parent_slot, > + cow_ret, search_start, 0, nest); > } > ALLOW_ERROR_INJECTION(btrfs_cow_block, ERRNO); >
diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c index 693dc27ffb89..185985a337b3 100644 --- a/fs/btrfs/ctree.c +++ b/fs/btrfs/ctree.c @@ -654,6 +654,8 @@ int btrfs_force_cow_block(struct btrfs_trans_handle *trans, goto error_unlock_cow; } } + + trace_btrfs_cow_block(root, buf, cow); if (unlock_orig) btrfs_tree_unlock(buf); free_extent_buffer_stale(buf); @@ -710,7 +712,6 @@ 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); @@ -751,12 +752,8 @@ 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_force_cow_block(trans, root, buf, parent, parent_slot, - cow_ret, search_start, 0, nest); - - trace_btrfs_cow_block(root, buf, *cow_ret); - - return ret; + return btrfs_force_cow_block(trans, root, buf, parent, parent_slot, + cow_ret, search_start, 0, nest); } ALLOW_ERROR_INJECTION(btrfs_cow_block, ERRNO);