[PATCH] xfs: hold xfs_buf locked between shortform->leaf conversion and the addition of an attribute

alex
2017-08-09T11:06:26Z

From: Alex Lyakas <alex@zadarastorage.com>

The new attribute leaf buffer is not held locked across
the transaction roll between the shortform->leaf modification
and the addition of the new entry. As a result, the attribute
buffer modification being made is not atomic from
an operational perspective. Hence the AIL push can grab it in
the transient state of "just created" after the initial
transaction is rolled, because the buffer has been released.
This leads to xfs_attr3_leaf_verify() asserting that
hdr.count is zero, treating this as in-memory corruption,
and shutting down the filesystem.

Signed-off-by: Alex Lyakas <alex@zadarastorage.com>
---
fs/xfs/libxfs/xfs_attr.c | 19 ++++++++++++++++++-
fs/xfs/libxfs/xfs_attr_leaf.c | 4 +++-
fs/xfs/libxfs/xfs_attr_leaf.h | 3 ++-
3 files changed, 23 insertions(+), 3 deletions(-)

diff --git a/fs/xfs/libxfs/xfs_attr.c b/fs/xfs/libxfs/xfs_attr.c
index de7b9bd..982e322 100644
--- a/fs/xfs/libxfs/xfs_attr.c
+++ b/fs/xfs/libxfs/xfs_attr.c
@@ -216,10 +216,11 @@
struct xfs_defer_ops dfops;
struct xfs_trans_res tres;
xfs_fsblock_t firstblock;
int rsvd = (flags & ATTR_ROOT) != 0;
int error, err2, local;
+ struct xfs_buf *leaf_bp = NULL;

XFS_STATS_INC(mp, xs_attr_set);

if (XFS_FORCED_SHUTDOWN(dp->i_mount))
return -EIO;
@@ -325,11 +326,17 @@
/*
* It won't fit in the shortform, transform to a leaf block.
* GROT: another possible req'mt for a double-split btree op.
*/
xfs_defer_init(args.dfops, args.firstblock);
- error = xfs_attr_shortform_to_leaf(&args);
+ error = xfs_attr_shortform_to_leaf(&args, &leaf_bp);
+ /*
+ * Prevent the leaf buffer from being unlocked
+ * when "args.trans" transaction commits.
+ */
+ if (leaf_bp)
+ xfs_trans_bhold(args.trans, leaf_bp);
if (!error)
error = xfs_defer_finish(&args.trans, args.dfops, dp);
if (error) {
args.trans = NULL;
xfs_defer_cancel(&dfops);
@@ -343,10 +350,18 @@

error = xfs_trans_roll(&args.trans, dp);
if (error)
goto out;

+ /*
+ * Rejoin the leaf buffer to the new transaction.
+ * This allows a subsequent read to find the buffer in the
+ * transaction (and avoid a deadlock).
+ */
+ xfs_trans_bjoin(args.trans, leaf_bp);
+ /* Prevent from being released at the end of the function */
+ leaf_bp = NULL;
}

if (xfs_bmap_one_block(dp, XFS_ATTR_FORK))
error = xfs_attr_leaf_addname(&args);
else
@@ -374,10 +389,12 @@
return error;

out:
if (args.trans)
xfs_trans_cancel(args.trans);
+ if (leaf_bp)
+ xfs_buf_relse(leaf_bp);
xfs_iunlock(dp, XFS_ILOCK_EXCL);
return error;
}

/*
diff --git a/fs/xfs/libxfs/xfs_attr_leaf.c b/fs/xfs/libxfs/xfs_attr_leaf.c
index c6c15e5..ab73e4b 100644
--- a/fs/xfs/libxfs/xfs_attr_leaf.c
+++ b/fs/xfs/libxfs/xfs_attr_leaf.c
@@ -738,13 +738,14 @@ STATIC void xfs_attr3_leaf_moveents(struct xfs_da_args *args,
return -ENOATTR;
}

/*
* Convert from using the shortform to the leaf.
+ * Upon success, return the leaf buffer.
*/
int
-xfs_attr_shortform_to_leaf(xfs_da_args_t *args)
+xfs_attr_shortform_to_leaf(xfs_da_args_t *args, struct xfs_buf **bpp)
{
xfs_inode_t *dp;
xfs_attr_shortform_t *sf;
xfs_attr_sf_entry_t *sfe;
xfs_da_args_t nargs;
@@ -820,10 +821,11 @@ STATIC void xfs_attr3_leaf_moveents(struct xfs_da_args *args,
if (error)
goto out;
sfe = XFS_ATTR_SF_NEXTENTRY(sfe);
}
error = 0;
+ *bpp = bp;

out:
kmem_free(tmpbuffer);
return error;
}
diff --git a/fs/xfs/libxfs/xfs_attr_leaf.h b/fs/xfs/libxfs/xfs_attr_leaf.h
index f7dda0c..2b3c69df 100644
--- a/fs/xfs/libxfs/xfs_attr_leaf.h
+++ b/fs/xfs/libxfs/xfs_attr_leaf.h
@@ -46,11 +46,12 @@
*/
void xfs_attr_shortform_create(struct xfs_da_args *args);
void xfs_attr_shortform_add(struct xfs_da_args *args, int forkoff);
int xfs_attr_shortform_lookup(struct xfs_da_args *args);
int xfs_attr_shortform_getvalue(struct xfs_da_args *args);
-int xfs_attr_shortform_to_leaf(struct xfs_da_args *args);
+int xfs_attr_shortform_to_leaf(struct xfs_da_args *args,
+ struct xfs_buf **bpp);
int xfs_attr_shortform_remove(struct xfs_da_args *args);
int xfs_attr_shortform_allfit(struct xfs_buf *bp, struct xfs_inode *dp);
int xfs_attr_shortform_bytesfit(struct xfs_inode *dp, int bytes);
void xfs_attr_fork_remove(struct xfs_inode *ip, struct xfs_trans *tp);

--
1.9.1