btrfs: fix potential deadlock in the search ioctl
With the conversion of the tree locks to rwsem I got the following lockdep splat: ====================================================== WARNING: possible circular locking dependency detected 5.8.0-rc7-00165-g04ec4da5f45f-dirty #922 Not tainted ------------------------------------------------------ compsize/11122 is trying to acquire lock: ffff889fabca8768 (&mm->mmap_lock#2){++++}-{3:3}, at: __might_fault+0x3e/0x90 but task is already holding lock: ffff889fe720fe40 (btrfs-fs-00){++++}-{3:3}, at: __btrfs_tree_read_lock+0x39/0x180 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #2 (btrfs-fs-00){++++}-{3:3}: down_write_nested+0x3b/0x70 __btrfs_tree_lock+0x24/0x120 btrfs_search_slot+0x756/0x990 btrfs_lookup_inode+0x3a/0xb4 __btrfs_update_delayed_inode+0x93/0x270 btrfs_async_run_delayed_root+0x168/0x230 btrfs_work_helper+0xd4/0x570 process_one_work+0x2ad/0x5f0 worker_thread+0x3a/0x3d0 kthread+0x133/0x150 ret_from_fork+0x1f/0x30 -> #1 (&delayed_node->mutex){+.+.}-{3:3}: __mutex_lock+0x9f/0x930 btrfs_delayed_update_inode+0x50/0x440 btrfs_update_inode+0x8a/0xf0 btrfs_dirty_inode+0x5b/0xd0 touch_atime+0xa1/0xd0 btrfs_file_mmap+0x3f/0x60 mmap_region+0x3a4/0x640 do_mmap+0x376/0x580 vm_mmap_pgoff+0xd5/0x120 ksys_mmap_pgoff+0x193/0x230 do_syscall_64+0x50/0x90 entry_SYSCALL_64_after_hwframe+0x44/0xa9 -> #0 (&mm->mmap_lock#2){++++}-{3:3}: __lock_acquire+0x1272/0x2310 lock_acquire+0x9e/0x360 __might_fault+0x68/0x90 _copy_to_user+0x1e/0x80 copy_to_sk.isra.32+0x121/0x300 search_ioctl+0x106/0x200 btrfs_ioctl_tree_search_v2+0x7b/0xf0 btrfs_ioctl+0x106f/0x30a0 ksys_ioctl+0x83/0xc0 __x64_sys_ioctl+0x16/0x20 do_syscall_64+0x50/0x90 entry_SYSCALL_64_after_hwframe+0x44/0xa9 other info that might help us debug this: Chain exists of: &mm->mmap_lock#2 --> &delayed_node->mutex --> btrfs-fs-00 Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(btrfs-fs-00); lock(&delayed_node->mutex); lock(btrfs-fs-00); lock(&mm->mmap_lock#2); *** DEADLOCK *** 1 lock held by compsize/11122: #0: ffff889fe720fe40 (btrfs-fs-00){++++}-{3:3}, at: __btrfs_tree_read_lock+0x39/0x180 stack backtrace: CPU: 17 PID: 11122 Comm: compsize Kdump: loaded Not tainted 5.8.0-rc7-00165-g04ec4da5f45f-dirty #922 Hardware name: Quanta Tioga Pass Single Side 01-0030993006/Tioga Pass Single Side, BIOS F08_3A18 12/20/2018 Call Trace: dump_stack+0x78/0xa0 check_noncircular+0x165/0x180 __lock_acquire+0x1272/0x2310 lock_acquire+0x9e/0x360 ? __might_fault+0x3e/0x90 ? find_held_lock+0x72/0x90 __might_fault+0x68/0x90 ? __might_fault+0x3e/0x90 _copy_to_user+0x1e/0x80 copy_to_sk.isra.32+0x121/0x300 ? btrfs_search_forward+0x2a6/0x360 search_ioctl+0x106/0x200 btrfs_ioctl_tree_search_v2+0x7b/0xf0 btrfs_ioctl+0x106f/0x30a0 ? __do_sys_newfstat+0x5a/0x70 ? ksys_ioctl+0x83/0xc0 ksys_ioctl+0x83/0xc0 __x64_sys_ioctl+0x16/0x20 do_syscall_64+0x50/0x90 entry_SYSCALL_64_after_hwframe+0x44/0xa9 The problem is we're doing a copy_to_user() while holding tree locks, which can deadlock if we have to do a page fault for the copy_to_user(). This exists even without my locking changes, so it needs to be fixed. Rework the search ioctl to do the pre-fault and then copy_to_user_nofault for the copying. CC: stable@vger.kernel.org # 4.4+ Reviewed-by: Filipe Manana <fdmanana@suse.com> Signed-off-by: Josef Bacik <josef@toxicpanda.com> Reviewed-by: David Sterba <dsterba@suse.com> Signed-off-by: David Sterba <dsterba@suse.com>
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9771a5cf93
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@ -5653,9 +5653,9 @@ void read_extent_buffer(const struct extent_buffer *eb, void *dstv,
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}
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}
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}
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}
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int read_extent_buffer_to_user(const struct extent_buffer *eb,
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int read_extent_buffer_to_user_nofault(const struct extent_buffer *eb,
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void __user *dstv,
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void __user *dstv,
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unsigned long start, unsigned long len)
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unsigned long start, unsigned long len)
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{
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{
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size_t cur;
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size_t cur;
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size_t offset;
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size_t offset;
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@ -5675,7 +5675,7 @@ int read_extent_buffer_to_user(const struct extent_buffer *eb,
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cur = min(len, (PAGE_SIZE - offset));
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cur = min(len, (PAGE_SIZE - offset));
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kaddr = page_address(page);
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kaddr = page_address(page);
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if (copy_to_user(dst, kaddr + offset, cur)) {
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if (copy_to_user_nofault(dst, kaddr + offset, cur)) {
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ret = -EFAULT;
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ret = -EFAULT;
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break;
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break;
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}
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}
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@ -241,9 +241,9 @@ int memcmp_extent_buffer(const struct extent_buffer *eb, const void *ptrv,
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void read_extent_buffer(const struct extent_buffer *eb, void *dst,
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void read_extent_buffer(const struct extent_buffer *eb, void *dst,
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unsigned long start,
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unsigned long start,
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unsigned long len);
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unsigned long len);
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int read_extent_buffer_to_user(const struct extent_buffer *eb,
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int read_extent_buffer_to_user_nofault(const struct extent_buffer *eb,
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void __user *dst, unsigned long start,
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void __user *dst, unsigned long start,
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unsigned long len);
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unsigned long len);
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void write_extent_buffer_fsid(const struct extent_buffer *eb, const void *src);
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void write_extent_buffer_fsid(const struct extent_buffer *eb, const void *src);
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void write_extent_buffer_chunk_tree_uuid(const struct extent_buffer *eb,
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void write_extent_buffer_chunk_tree_uuid(const struct extent_buffer *eb,
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const void *src);
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const void *src);
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@ -2086,9 +2086,14 @@ static noinline int copy_to_sk(struct btrfs_path *path,
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sh.len = item_len;
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sh.len = item_len;
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sh.transid = found_transid;
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sh.transid = found_transid;
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/* copy search result header */
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/*
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if (copy_to_user(ubuf + *sk_offset, &sh, sizeof(sh))) {
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* Copy search result header. If we fault then loop again so we
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ret = -EFAULT;
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* can fault in the pages and -EFAULT there if there's a
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* problem. Otherwise we'll fault and then copy the buffer in
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* properly this next time through
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*/
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if (copy_to_user_nofault(ubuf + *sk_offset, &sh, sizeof(sh))) {
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ret = 0;
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goto out;
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goto out;
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}
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}
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@ -2096,10 +2101,14 @@ static noinline int copy_to_sk(struct btrfs_path *path,
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if (item_len) {
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if (item_len) {
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char __user *up = ubuf + *sk_offset;
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char __user *up = ubuf + *sk_offset;
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/* copy the item */
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/*
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if (read_extent_buffer_to_user(leaf, up,
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* Copy the item, same behavior as above, but reset the
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item_off, item_len)) {
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* * sk_offset so we copy the full thing again.
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ret = -EFAULT;
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*/
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if (read_extent_buffer_to_user_nofault(leaf, up,
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item_off, item_len)) {
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ret = 0;
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*sk_offset -= sizeof(sh);
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goto out;
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goto out;
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}
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}
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@ -2184,6 +2193,10 @@ static noinline int search_ioctl(struct inode *inode,
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key.offset = sk->min_offset;
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key.offset = sk->min_offset;
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while (1) {
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while (1) {
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ret = fault_in_pages_writeable(ubuf, *buf_size - sk_offset);
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if (ret)
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break;
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ret = btrfs_search_forward(root, &key, path, sk->min_transid);
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ret = btrfs_search_forward(root, &key, path, sk->min_transid);
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if (ret != 0) {
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if (ret != 0) {
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if (ret > 0)
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if (ret > 0)
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