On Wed, Apr 18, 2018 at 6:17 AM, David Sterba <dsterba@xxxxxxxx> wrote:
> The last update to readdir introduced a temporary buffer to store the
> emitted readdir data, but as there are file names of variable length,
> there's a lot of unaligned access.
>
> This was observed on a sparc64 machine:
>
> Kernel unaligned access at TPC[102f3080] btrfs_real_readdir+0x51c/0x718 [btrfs]
>
Reviewed-by: Liu Bo <bo.liu@xxxxxxxxxxxxxxxxx>
thanks,
liubo
> Fixes: 23b5ec74943 ("btrfs: fix readdir deadlock with pagefault")
> CC: stable@xxxxxxxxxxxxxxx # 4.14+
> Reported-and-tested-by: René Rebe <rene@xxxxxxxxxxxxx>
> Signed-off-by: David Sterba <dsterba@xxxxxxxx>
> ---
> fs/btrfs/inode.c | 20 ++++++++++++--------
> 1 file changed, 12 insertions(+), 8 deletions(-)
>
> diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
> index e064c49c9a9a..d241285a0d2a 100644
> --- a/fs/btrfs/inode.c
> +++ b/fs/btrfs/inode.c
> @@ -31,6 +31,7 @@
> #include <linux/uio.h>
> #include <linux/magic.h>
> #include <linux/iversion.h>
> +#include <asm/unaligned.h>
> #include "ctree.h"
> #include "disk-io.h"
> #include "transaction.h"
> @@ -5905,11 +5906,13 @@ static int btrfs_filldir(void *addr, int entries, struct dir_context *ctx)
> struct dir_entry *entry = addr;
> char *name = (char *)(entry + 1);
>
> - ctx->pos = entry->offset;
> - if (!dir_emit(ctx, name, entry->name_len, entry->ino,
> - entry->type))
> + ctx->pos = get_unaligned(&entry->offset);
> + if (!dir_emit(ctx, name, get_unaligned(&entry->name_len),
> + get_unaligned(&entry->ino),
> + get_unaligned(&entry->type)))
> return 1;
> - addr += sizeof(struct dir_entry) + entry->name_len;
> + addr += sizeof(struct dir_entry) +
> + get_unaligned(&entry->name_len);
> ctx->pos++;
> }
> return 0;
> @@ -5999,14 +6002,15 @@ static int btrfs_real_readdir(struct file *file, struct dir_context *ctx)
> }
>
> entry = addr;
> - entry->name_len = name_len;
> + put_unaligned(name_len, &entry->name_len);
> name_ptr = (char *)(entry + 1);
> read_extent_buffer(leaf, name_ptr, (unsigned long)(di + 1),
> name_len);
> - entry->type = btrfs_filetype_table[btrfs_dir_type(leaf, di)];
> + put_unaligned(btrfs_filetype_table[btrfs_dir_type(leaf, di)],
> + &entry->type);
> btrfs_dir_item_key_to_cpu(leaf, di, &location);
> - entry->ino = location.objectid;
> - entry->offset = found_key.offset;
> + put_unaligned(location.objectid, &entry->ino);
> + put_unaligned(found_key.offset, &entry->offset);
> entries++;
> addr += sizeof(struct dir_entry) + name_len;
> total_len += sizeof(struct dir_entry) + name_len;
> --
> 2.16.2
>
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