Re: [PATCH v3] f2fs: fix to avoid accessing xattr across the boundary

From: Randall Huang
Date: Wed Apr 10 2019 - 05:27:27 EST

On Tue, Apr 09, 2019 at 06:22:55PM +0800, Chao Yu wrote:
> On 2019/4/9 16:53, Randall Huang wrote:
> > When we traverse xattr entries via __find_xattr(),
> > if the raw filesystem content is faked or any hardware failure occurs,
> > out-of-bound error can be detected by KASAN.
> > Fix the issue by introducing boundary check.
> >
> > [ 38.402878] c7 1827 BUG: KASAN: slab-out-of-bounds in f2fs_getxattr+0x518/0x68c
> > [ 38.402891] c7 1827 Read of size 4 at addr ffffffc0b6fb35dc by task
> > [ 38.402935] c7 1827 Call trace:
> > [ 38.402952] c7 1827 [<ffffff900809003c>] dump_backtrace+0x0/0x6bc
> > [ 38.402966] c7 1827 [<ffffff9008090030>] show_stack+0x20/0x2c
> > [ 38.402981] c7 1827 [<ffffff900871ab10>] dump_stack+0xfc/0x140
> > [ 38.402995] c7 1827 [<ffffff9008325c40>] print_address_description+0x80/0x2d8
> > [ 38.403009] c7 1827 [<ffffff900832629c>] kasan_report_error+0x198/0x1fc
> > [ 38.403022] c7 1827 [<ffffff9008326104>] kasan_report_error+0x0/0x1fc
> > [ 38.403037] c7 1827 [<ffffff9008325000>] __asan_load4+0x1b0/0x1b8
> > [ 38.403051] c7 1827 [<ffffff90085fcc44>] f2fs_getxattr+0x518/0x68c
> > [ 38.403066] c7 1827 [<ffffff90085fc508>] f2fs_xattr_generic_get+0xb0/0xd0
> > [ 38.403080] c7 1827 [<ffffff9008395708>] __vfs_getxattr+0x1f4/0x1fc
> > [ 38.403096] c7 1827 [<ffffff9008621bd0>] inode_doinit_with_dentry+0x360/0x938
> > [ 38.403109] c7 1827 [<ffffff900862d6cc>] selinux_d_instantiate+0x2c/0x38
> > [ 38.403123] c7 1827 [<ffffff900861b018>] security_d_instantiate+0x68/0x98
> > [ 38.403136] c7 1827 [<ffffff9008377db8>] d_splice_alias+0x58/0x348
> > [ 38.403149] c7 1827 [<ffffff900858d16c>] f2fs_lookup+0x608/0x774
> > [ 38.403163] c7 1827 [<ffffff900835eacc>] lookup_slow+0x1e0/0x2cc
> > [ 38.403177] c7 1827 [<ffffff9008367fe0>] walk_component+0x160/0x520
> > [ 38.403190] c7 1827 [<ffffff9008369ef4>] path_lookupat+0x110/0x2b4
> > [ 38.403203] c7 1827 [<ffffff900835dd38>] filename_lookup+0x1d8/0x3a8
> > [ 38.403216] c7 1827 [<ffffff900835eeb0>] user_path_at_empty+0x54/0x68
> > [ 38.403229] c7 1827 [<ffffff9008395f44>] SyS_getxattr+0xb4/0x18c
> > [ 38.403241] c7 1827 [<ffffff9008084200>] el0_svc_naked+0x34/0x38
> >
> > Bug: 126558260
> >
> > Signed-off-by: Randall Huang <huangrandall@xxxxxxxxxx>
> > ---
> > v2:
> > * return EFAULT if OOB error is detected
> >
> > v3:
> > * fix typo in setxattr()
> > ---
> > fs/f2fs/xattr.c | 31 +++++++++++++++++++++++++++----
> > 1 file changed, 27 insertions(+), 4 deletions(-)
> >
> > diff --git a/fs/f2fs/xattr.c b/fs/f2fs/xattr.c
> > index 848a785abe25..381f14b02a78 100644
> > --- a/fs/f2fs/xattr.c
> > +++ b/fs/f2fs/xattr.c
> > @@ -202,12 +202,17 @@ static inline const struct xattr_handler *f2fs_xattr_handler(int index)
> > return handler;
> > }
> >
> > -static struct f2fs_xattr_entry *__find_xattr(void *base_addr, int index,
> > - size_t len, const char *name)
> > +static struct f2fs_xattr_entry *__find_xattr(void *base_addr,
> > + unsigned int max_size, int index,
> > + size_t len, const char *name)
> > {
> > struct f2fs_xattr_entry *entry;
> > + void *max_addr = base_addr + ENTRY_SIZE(XATTR_ENTRY(base_addr)) +
> > + max_size - 1;
>
> Hi Randall,
>
> I think this is not right, I enable noinline_xattr mount option, and add
> printk to see the status here, it shows
>
> __find_xattr, base_addr:ffff8e709ba92000, max_addr:ffff8e709baa131f, max_size:4
>
> ffff8e709baa131f - ffff8e709ba92000 = F31F
>
I would like to try another way.
The key is the pointer of entry should never run over the boundary of txattr
allocated in lookup_all_xattrs().

I will send v4.

> >
> > list_for_each_xattr(entry, base_addr) {
> > + if ((void *)entry + sizeof(__u32) > max_addr)
> > + return NULL;
> > if (entry->e_name_index != index)
> > continue;
> > if (entry->e_name_len != len)
> > @@ -301,6 +306,7 @@ static int lookup_all_xattrs(struct inode *inode, struct page *ipage,
> > nid_t xnid = F2FS_I(inode)->i_xattr_nid;
> > unsigned int size = xnid ? VALID_XATTR_BLOCK_SIZE : 0;
> > unsigned int inline_size = inline_xattr_size(inode);
> > + unsigned int max_size = inline_size + size + XATTR_PADDING_SIZE;
> > int err = 0;
> >
> > if (!size && !inline_size)
> > @@ -323,6 +329,7 @@ static int lookup_all_xattrs(struct inode *inode, struct page *ipage,
> > *base_size = inline_size;
> > goto check;
> > }
> > + max_size -= inline_size;
>
> The cur_addr pointer may point to middle of inline xattr space due to below code? we
> should consider such case here.
>
> if (last_addr)
> cur_addr = XATTR_HDR(last_addr) - 1;
>
> > }
> >
> > /* read from xattr node block */
> > @@ -330,6 +337,8 @@ static int lookup_all_xattrs(struct inode *inode, struct page *ipage,
> > err = read_xattr_block(inode, txattr_addr);
> > if (err)
> > goto out;
> > +
> > + max_size -= size;
>
> We should not shrink max_size after loading xattr block's data.
>
> Thanks,
>
> > }
> >
> > if (last_addr)
> > @@ -337,7 +346,12 @@ static int lookup_all_xattrs(struct inode *inode, struct page *ipage,
> > else
> > cur_addr = txattr_addr;
> >
> > - *xe = __find_xattr(cur_addr, index, len, name);
> > + *xe = __find_xattr(cur_addr, max_size, index, len, name);
> > + if (!*xe) {
> > + err = -EFAULT;
> > + goto out;
> > + }
> > +
> > check:
> > if (IS_XATTR_LAST_ENTRY(*xe)) {
> > err = -ENODATA;
> > @@ -585,6 +599,11 @@ static int __f2fs_setxattr(struct inode *inode, int index,
> > int found, newsize;
> > size_t len;
> > __u32 new_hsize;
> > + nid_t xnid = F2FS_I(inode)->i_xattr_nid;
> > + unsigned int xattr_nid_size = xnid ? VALID_XATTR_BLOCK_SIZE : 0;
> > + unsigned int inline_size = inline_xattr_size(inode);
> > + unsigned int max_size = inline_size + xattr_nid_size +
> > + XATTR_PADDING_SIZE;
> > int error = 0;
> >
> > if (name == NULL)
> > @@ -606,7 +625,11 @@ static int __f2fs_setxattr(struct inode *inode, int index,
> > return error;
> >
> > /* find entry with wanted name. */
> > - here = __find_xattr(base_addr, index, len, name);
> > + here = __find_xattr(base_addr, max_size, index, len, name);
> > + if (!here) {
> > + error = -EFAULT;
> > + goto exit;
> > + }
> >
> > found = IS_XATTR_LAST_ENTRY(here) ? 0 : 1;
> >
> >