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Subject[PATCH 5.0 10/46] staging: erofs: fix race of initializing xattrs of a inode at the same time
Date
5.0-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Gao Xiang <gaoxiang25@huawei.com>

commit 62dc45979f3f8cb0ea67302a93bff686f0c46c5a upstream.

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+
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Gao Xiang <gaoxiang25@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/staging/erofs/internal.h | 11 +++++++---
drivers/staging/erofs/xattr.c | 41 +++++++++++++++++++++++++++------------
2 files changed, 37 insertions(+), 15 deletions(-)

--- a/drivers/staging/erofs/internal.h
+++ b/drivers/staging/erofs/internal.h
@@ -354,12 +354,17 @@ static inline erofs_off_t iloc(struct er
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 */
--- a/drivers/staging/erofs/xattr.c
+++ b/drivers/staging/erofs/xattr.c
@@ -44,18 +44,25 @@ static inline void xattr_iter_end_final(

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 (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 (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 inod
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 inod
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 inod
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 inod
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 inod
}
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;
}

/*

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