On Wed, Jul 27, 2022 at 04:52:30PM +0800, ChenXiaoSong wrote:
> 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);
Heh. Is this worth an fstest? It probably is, since prior to 5.20 this
would have been a UAF bug on top of a NULL deref.
> 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().
Nit: it's ILOCK, not i_lock. Otherwise... this looks correct to me --
take the IOLOCK and ILOCK in shared mode before accessing the inode fork
structures.
Do you have any suggestions for Fixes:? I suspect this has been broken
for quite some time.
No need to fix the nit, I'll do that when I commit this.
Reviewed-by: Darrick J. Wong <djwong@xxxxxxxxxx>
--D
> Signed-off-by: ChenXiaoSong <chenxiaosong2@xxxxxxxxxx>
> Signed-off-by: Guo Xuenan <guoxuenan@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 74f96e1aa5cd..04d0c2bff67c 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_inode_has_attr_fork(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:
> --
> 2.31.1
>
