New subject: [PATCH] staging: erofs: fix race of initializing xattrs of a inode at the same time

14 Feb 2019

In real scenario, there could be several threads accessing xattrs
of the same xattr-uninitialized inode, and init_inode_xattrs()
almost at the same time.
That's actually an unexpected behavior, this patch closes the race.
Fixes: b17500a0fdba ("staging: erofs: introduce xattr & acl support")
Cc: stable@vger.kernel.org # 4.19+
Signed-off-by: Gao Xiang gaoxiang25@huawei.com
---
 drivers/staging/erofs/internal.h | 11 ++++++++---
 drivers/staging/erofs/xattr.c    | 41 ++++++++++++++++++++++++++++------------
 2 files changed, 37 insertions(+), 15 deletions(-)

diff --git a/drivers/staging/erofs/internal.h b/drivers/staging/erofs/internal.h
index 3a27c255950b..e3bfde00c7d2 100644
--- a/drivers/staging/erofs/internal.h
+++ b/drivers/staging/erofs/internal.h
@@ -327,12 +327,17 @@ static inline erofs_off_t iloc(struct erofs_sb_info *sbi, erofs_nid_t nid)
    return blknr_to_addr(sbi->meta_blkaddr) + (nid << sbi->islotbits);
 }
-#define inode_set_inited_xattr(inode)   (EROFS_V(inode)->flags |= 1)
-#define inode_has_inited_xattr(inode)   (EROFS_V(inode)->flags & 1)
+/* atomic flag definitions */
+#define EROFS_V_EA_INITED_BIT	0
+
+/* bitlock definitions (arranged in reverse order) */
+#define EROFS_V_BL_XATTR_BIT	(BITS_PER_LONG - 1)
struct erofs_vnode {
    erofs_nid_t nid;
-	unsigned int flags;
+
+	/* atomic flags (including bitlocks) */
+	unsigned long flags;
unsigned char data_mapping_mode;
    /* inline size in bytes */
diff --git a/drivers/staging/erofs/xattr.c b/drivers/staging/erofs/xattr.c
index 8c48b0ab31fd..a188aad00bf8 100644
--- a/drivers/staging/erofs/xattr.c
+++ b/drivers/staging/erofs/xattr.c
@@ -44,18 +44,25 @@ static inline void xattr_iter_end_final(struct xattr_iter *it)
static int init_inode_xattrs(struct inode *inode)
 {
+	struct erofs_vnode *const vi = EROFS_V(inode);
    struct xattr_iter it;
    unsigned int i;
    struct erofs_xattr_ibody_header *ih;
    struct super_block *sb;
    struct erofs_sb_info *sbi;
-	struct erofs_vnode *vi;
    bool atomic_map;
+	int ret = 0;
-	if (likely(inode_has_inited_xattr(inode)))
+	/* the most case is that xattrs of this inode are initialized. */
+	if (likely(test_bit(EROFS_V_EA_INITED_BIT, &vi->flags)))
    	return 0;
-	vi = EROFS_V(inode);
+	if (wait_on_bit_lock(&vi->flags, EROFS_V_BL_XATTR_BIT, TASK_KILLABLE))
+		return -ERESTARTSYS;
+
+	/* someone has initialized xattrs for us? */
+	if (unlikely(test_bit(EROFS_V_EA_INITED_BIT, &vi->flags)))
+		goto out_unlock;
/*
     * bypass all xattr operations if ->xattr_isize is not greater than
@@ -68,13 +75,16 @@ static int init_inode_xattrs(struct inode *inode)
    if (vi->xattr_isize == sizeof(struct erofs_xattr_ibody_header)) {
    	errln("xattr_isize %d of nid %llu is not supported yet",
    	      vi->xattr_isize, vi->nid);
-		return -ENOTSUPP;
+		ret = -ENOTSUPP;
+		goto out_unlock;
    } else if (vi->xattr_isize < sizeof(struct erofs_xattr_ibody_header)) {
    	if (unlikely(vi->xattr_isize)) {
    		DBG_BUGON(1);
-			return -EIO;	/* xattr ondisk layout error */
+			ret = -EIO;
+			goto out_unlock;	/* xattr ondisk layout error */
    	}
-		return -ENOATTR;
+		ret = -ENOATTR;
+		goto out_unlock;
    }
sb = inode->i_sb;
@@ -83,8 +93,10 @@ static int init_inode_xattrs(struct inode *inode)
    it.ofs = erofs_blkoff(iloc(sbi, vi->nid) + vi->inode_isize);
it.page = erofs_get_inline_page(inode, it.blkaddr);
-	if (IS_ERR(it.page))
-		return PTR_ERR(it.page);
+	if (IS_ERR(it.page)) {
+		ret = PTR_ERR(it.page);
+		goto out_unlock;
+	}
/* read in shared xattr array (non-atomic, see kmalloc below) */
    it.kaddr = kmap(it.page);
@@ -97,7 +109,8 @@ static int init_inode_xattrs(struct inode *inode)
    					sizeof(uint), GFP_KERNEL);
    if (vi->xattr_shared_xattrs == NULL) {
    	xattr_iter_end(&it, atomic_map);
-		return -ENOMEM;
+		ret = -ENOMEM;
+		goto out_unlock;
    }
/* let's skip ibody header */
@@ -114,7 +127,8 @@ static int init_inode_xattrs(struct inode *inode)
    		if (IS_ERR(it.page)) {
    			kfree(vi->xattr_shared_xattrs);
    			vi->xattr_shared_xattrs = NULL;
-				return PTR_ERR(it.page);
+				ret = PTR_ERR(it.page);
+				goto out_unlock;
    		}
it.kaddr = kmap_atomic(it.page);
@@ -127,8 +141,11 @@ static int init_inode_xattrs(struct inode *inode)
    }
    xattr_iter_end(&it, atomic_map);
-	inode_set_inited_xattr(inode);
-	return 0;
+	set_bit(EROFS_V_EA_INITED_BIT, &vi->flags);
+
+out_unlock:
+	clear_and_wake_up_bit(EROFS_V_BL_XATTR_BIT, &vi->flags);
+	return ret;
 }
/*
-- 
2.14.4


    

[PREVIEW] [PATCH] staging: erofs: fix race of initializing xattrs of a inode at the same time