Re: [PATCH] btrfs: send: reject extents for non-regular inodes

[Qu Wenruo <wqu@suse.com>]

在 2026/8/17 22:50, ZhengYuan Huang 写道:
> [BUG]
> A corrupted subvolume tree can leave an EXTENT_DATA item attached to an
> inode whose mode is not S_IFREG or S_IFLNK. During send, such an item can
> be treated as file data and crash through a NULL address_space operation:
> 
>    BUG: kernel NULL pointer dereference, address: 0000000000000000
>    #PF: supervisor instruction fetch in kernel mode
>    #PF: error_code(0x0010) - not-present page
>    Call Trace:
>      <TASK>
>      read_pages+0x80b/0xb30 mm/readahead.c:173
>      page_cache_ra_unbounded+0x40d/0x890 mm/readahead.c:302
>      do_page_cache_ra mm/readahead.c:332 [inline]
>      page_cache_ra_order+0xa16/0xcd0 mm/readahead.c:535
>      page_cache_sync_ra+0x5ce/0x9d0 mm/readahead.c:626
>      page_cache_sync_readahead include/linux/pagemap.h:1379 [inline]
>      put_file_data fs/btrfs/send.c:5224 [inline]
>      send_write fs/btrfs/send.c:5291 [inline]
>      send_extent_data+0x16b2/0x29b0 fs/btrfs/send.c:5715
>      send_write_or_clone fs/btrfs/send.c:6135 [inline]
>      process_extent+0x5d4/0x17b0 fs/btrfs/send.c:6504
>      changed_extent fs/btrfs/send.c:7079 [inline]
>      changed_cb+0x22f9/0x3cd0 fs/btrfs/send.c:7245
>      full_send_tree fs/btrfs/send.c:7318 [inline]
>      send_subvol fs/btrfs/send.c:7910 [inline]
>      btrfs_ioctl_send+0x46a9/0x57f0 fs/btrfs/send.c:8248
>      ...
> 
> [CAUSE]
> process_extent() skips extent items for symlinks but assumes every other
> inode with an extent item is a regular file. For a corrupted non-regular
> inode, btrfs_iget() does not install the regular file address_space
> operations. The readahead fallback can then call a NULL read_folio
> callback before the existing validation in btrfs_get_extent() can run.
> 
> [FIX]
> Reject extent items for inode types other than regular files and symlinks
> at the common send extent-processing boundary. Symlink handling is left
> unchanged because send emits symlink data from read_symlink(). This covers
> full, incremental and new-generation sends without adding a check to the
> regular I/O path.
> 
> Signed-off-by: ZhengYuan Huang <gality369@gmail.com>

Reviewed-by: Qu Wenruo <wqu@suse.com>

> ---
>   fs/btrfs/send.c | 7 +++++++
>   1 file changed, 7 insertions(+)
> 
> diff --git a/fs/btrfs/send.c b/fs/btrfs/send.c
> index dca3570168c7..f88623bbc491 100644
> --- a/fs/btrfs/send.c
> +++ b/fs/btrfs/send.c
> @@ -6417,6 +6417,13 @@ static int process_extent(struct send_ctx *sctx,
>   
>   	if (S_ISLNK(sctx->cur_inode_mode))
>   		return 0;
> +	if (unlikely(!S_ISREG(sctx->cur_inode_mode))) {
> +		btrfs_crit(sctx->send_root->fs_info,
> +			   "send: extent for non-regular inode %llu root %llu mode 0%llo",
> +			   key->objectid, btrfs_root_id(sctx->send_root),
> +			   sctx->cur_inode_mode & S_IFMT);
> +		return -EUCLEAN;
> +	}
>   
>   	if (sctx->parent_root && !sctx->cur_inode_new) {
>   		ret = is_extent_unchanged(sctx, path, key);