On Wed, Nov 15, 2023 at 06:28:25PM -0800, Leah Rumancik wrote:
> From: ChenXiaoSong <chenxiaosong2@xxxxxxxxxx>
>
> [ Upstream commit 001c179c4e26d04db8c9f5e3fef9558b58356be6 ]
>
> Reproducer:
> 1. fallocate -l 100M image
> 2. mkfs.xfs -f image
> 3. mount image /mnt
> 4. setxattr("/mnt", "trusted.overlay.upper", NULL, 0, XATTR_CREATE)
> 5. char arg[32] = "\x01\xff\x00\x00\x00\x00\x03\x00\x00\x00\x00\x00\x00"
> "\x00\x00\x00\x00\x00\x08\x00\x00\x00\xc6\x2a\xf7";
> fd = open("/mnt", O_RDONLY|O_DIRECTORY);
> ioctl(fd, _IOC(_IOC_READ|_IOC_WRITE, 0x58, 0x2c, 0x20), arg);
>
> NULL pointer dereference will occur when race happens between xfs_getbmap()
> and xfs_bmap_set_attrforkoff():
>
> ioctl | setxattr
> ----------------------------|---------------------------
> xfs_getbmap |
> xfs_ifork_ptr |
> xfs_inode_has_attr_fork |
> ip->i_forkoff == 0 |
> return NULL |
> ifp == NULL |
> | xfs_bmap_set_attrforkoff
> | ip->i_forkoff > 0
> xfs_inode_has_attr_fork |
> ip->i_forkoff > 0 |
> ifp == NULL |
> ifp->if_format |
>
> Fix this by locking i_lock before xfs_ifork_ptr().
>
> Fixes: abbf9e8a4507 ("xfs: rewrite getbmap using the xfs_iext_* helpers")
> Signed-off-by: ChenXiaoSong <chenxiaosong2@xxxxxxxxxx>
> Signed-off-by: Guo Xuenan <guoxuenan@xxxxxxxxxx>
> Reviewed-by: Darrick J. Wong <djwong@xxxxxxxxxx>
> [djwong: added fixes tag]
> Signed-off-by: Darrick J. Wong <djwong@xxxxxxxxxx>
> Signed-off-by: Leah Rumancik <leah.rumancik@xxxxxxxxx>
> Acked-by: Chandan Babu R <chandanbabu@xxxxxxxxxx>
> ---
> fs/xfs/xfs_bmap_util.c | 17 +++++++++--------
> 1 file changed, 9 insertions(+), 8 deletions(-)
>
> diff --git a/fs/xfs/xfs_bmap_util.c b/fs/xfs/xfs_bmap_util.c
> index fd2ad6a3019c..bea6cc26abf9 100644
> --- a/fs/xfs/xfs_bmap_util.c
> +++ b/fs/xfs/xfs_bmap_util.c
> @@ -439,29 +439,28 @@ xfs_getbmap(
> whichfork = XFS_COW_FORK;
> else
> whichfork = XFS_DATA_FORK;
> - ifp = XFS_IFORK_PTR(ip, whichfork);
>
> xfs_ilock(ip, XFS_IOLOCK_SHARED);
> switch (whichfork) {
> case XFS_ATTR_FORK:
> + lock = xfs_ilock_attr_map_shared(ip);
> if (!XFS_IFORK_Q(ip))
> - goto out_unlock_iolock;
> + goto out_unlock_ilock;
>
> max_len = 1LL << 32;
> - lock = xfs_ilock_attr_map_shared(ip);
> break;
> case XFS_COW_FORK:
> + lock = XFS_ILOCK_SHARED;
> + xfs_ilock(ip, lock);
> +
> /* No CoW fork? Just return */
> - if (!ifp)
> - goto out_unlock_iolock;
> + if (!XFS_IFORK_PTR(ip, whichfork))
> + goto out_unlock_ilock;
>
> if (xfs_get_cowextsz_hint(ip))
> max_len = mp->m_super->s_maxbytes;
> else
> max_len = XFS_ISIZE(ip);
> -
> - lock = XFS_ILOCK_SHARED;
> - xfs_ilock(ip, lock);
> break;
> case XFS_DATA_FORK:
> if (!(iflags & BMV_IF_DELALLOC) &&
> @@ -491,6 +490,8 @@ xfs_getbmap(
> break;
> }
>
> + ifp = XFS_IFORK_PTR(ip, whichfork);
> +
> switch (ifp->if_format) {
> case XFS_DINODE_FMT_EXTENTS:
> case XFS_DINODE_FMT_BTREE:
> --
> 2.43.0.rc0.421.g78406f8d94-goog
>
This patch breaks the build, how was it tested?
fs/xfs/xfs_bmap_util.c: In function ‘xfs_getbmap’:
fs/xfs/xfs_bmap_util.c:457:21: error: the comparison will always evaluate as ‘true’ for the address of ‘i_df’ will never be NULL [-Werror=address]
457 | if (!XFS_IFORK_PTR(ip, whichfork))
| ^
In file included from fs/xfs/xfs_bmap_util.c:16:
fs/xfs/xfs_inode.h:38:33: note: ‘i_df’ declared here
38 | struct xfs_ifork i_df; /* data fork */
| ^~~~
cc1: all warnings being treated as errors
