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]
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