Commit ce063129 authored by Gao Xiang's avatar Gao Xiang
Browse files

erofs: initialized fields can only be observed after bit is set 

Currently, although set_bit() & test_bit() pairs are used as a fast-
path for initialized configurations. However, these atomic ops are
actually relaxed forms. Instead, load-acquire & store-release form is
needed to make sure uninitialized fields won't be observed in advance
here (yet no such corresponding bitops so use full barriers instead.)

Link: https://lore.kernel.org/r/20210209130618.15838-1-hsiangkao@aol.com


Fixes: 62dc4597 ("staging: erofs: fix race of initializing xattrs of a inode at the same time")
Fixes: 152a333a ("staging: erofs: add compacted compression indexes support")
Cc: <stable@vger.kernel.org> # 5.3+
Reported-by: default avatarHuang Jianan <huangjianan@oppo.com>
Reviewed-by: default avatarChao Yu <yuchao0@huawei.com>
Signed-off-by: default avatarGao Xiang <hsiangkao@redhat.com>
parent bde54529

fs/erofs/xattr.c

+9 −1
Original line number Diff line number Diff line
@@ -48,8 +48,14 @@ static int init_inode_xattrs(struct inode *inode) 
	int ret = 0;



	/* the most case is that xattrs of this inode are initialized. */

	if (test_bit(EROFS_I_EA_INITED_BIT, &vi->flags))

	if (test_bit(EROFS_I_EA_INITED_BIT, &vi->flags)) {

		/*

		 * paired with smp_mb() at the end of the function to ensure

		 * fields will only be observed after the bit is set.

		 */

		smp_mb();

		return 0;

	}



	if (wait_on_bit_lock(&vi->flags, EROFS_I_BL_XATTR_BIT, TASK_KILLABLE))

		return -ERESTARTSYS;
@@ -137,6 +143,8 @@ static int init_inode_xattrs(struct inode *inode) 
	}

	xattr_iter_end(&it, atomic_map);



	/* paired with smp_mb() at the beginning of the function. */

	smp_mb();

	set_bit(EROFS_I_EA_INITED_BIT, &vi->flags);



out_unlock:

fs/erofs/zmap.c

+9 −1
Original line number Diff line number Diff line
@@ -36,8 +36,14 @@ static int z_erofs_fill_inode_lazy(struct inode *inode) 
	void *kaddr;

	struct z_erofs_map_header *h;



	if (test_bit(EROFS_I_Z_INITED_BIT, &vi->flags))

	if (test_bit(EROFS_I_Z_INITED_BIT, &vi->flags)) {

		/*

		 * paired with smp_mb() at the end of the function to ensure

		 * fields will only be observed after the bit is set.

		 */

		smp_mb();

		return 0;

	}



	if (wait_on_bit_lock(&vi->flags, EROFS_I_BL_Z_BIT, TASK_KILLABLE))

		return -ERESTARTSYS;
@@ -83,6 +89,8 @@ static int z_erofs_fill_inode_lazy(struct inode *inode) 


	vi->z_physical_clusterbits[1] = vi->z_logical_clusterbits +

					((h->h_clusterbits >> 5) & 7);

	/* paired with smp_mb() at the beginning of the function */

	smp_mb();

	set_bit(EROFS_I_Z_INITED_BIT, &vi->flags);

unmap_done:

	kunmap_atomic(kaddr);