* [PATCH] xfs: fix NULL pointer dereference in xfs_getbmap()
@ 2022-07-27 8:52 ChenXiaoSong
2022-07-27 15:16 ` Darrick J. Wong
0 siblings, 1 reply; 3+ messages in thread
From: ChenXiaoSong @ 2022-07-27 8:52 UTC (permalink / raw)
To: djwong
Cc: linux-xfs, linux-kernel, chenxiaosong2, guoxuenan,
liuyongqiang13, yi.zhang, zhangxiaoxu5
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().
Signed-off-by: ChenXiaoSong <chenxiaosong2@huawei.com>
Signed-off-by: Guo Xuenan <guoxuenan@huawei.com>
---
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
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH] xfs: fix NULL pointer dereference in xfs_getbmap()
2022-07-27 8:52 [PATCH] xfs: fix NULL pointer dereference in xfs_getbmap() ChenXiaoSong
@ 2022-07-27 15:16 ` Darrick J. Wong
2022-07-28 10:57 ` chenxiaosong (A)
0 siblings, 1 reply; 3+ messages in thread
From: Darrick J. Wong @ 2022-07-27 15:16 UTC (permalink / raw)
To: ChenXiaoSong
Cc: linux-xfs, linux-kernel, guoxuenan, liuyongqiang13, yi.zhang,
zhangxiaoxu5
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@kernel.org>
--D
> Signed-off-by: ChenXiaoSong <chenxiaosong2@huawei.com>
> Signed-off-by: Guo Xuenan <guoxuenan@huawei.com>
> ---
> 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
>
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] xfs: fix NULL pointer dereference in xfs_getbmap()
2022-07-27 15:16 ` Darrick J. Wong
@ 2022-07-28 10:57 ` chenxiaosong (A)
0 siblings, 0 replies; 3+ messages in thread
From: chenxiaosong (A) @ 2022-07-28 10:57 UTC (permalink / raw)
To: Darrick J. Wong
Cc: linux-xfs, linux-kernel, guoxuenan, liuyongqiang13, yi.zhang,
zhangxiaoxu5
在 2022/7/27 23:16, Darrick J. Wong 写道:
> 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.
I will try to add regression test to xfstests for this commit when it is
merged into mainline.
>
> 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.
The "Fixes:" label is: abbf9e8a4507 ("xfs: rewrite getbmap using the
xfs_iext_* helpers")
>
> No need to fix the nit, I'll do that when I commit this.
> Reviewed-by: Darrick J. Wong <djwong@kernel.org>
>
> --D
>
^ permalink raw reply [flat|nested] 3+ messages in thread
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2022-07-27 8:52 [PATCH] xfs: fix NULL pointer dereference in xfs_getbmap() ChenXiaoSong
2022-07-27 15:16 ` Darrick J. Wong
2022-07-28 10:57 ` chenxiaosong (A)
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