Re: [PATCH v5] f2fs: fix to avoid accessing xattr across the boundary

[Jaegeuk Kim]

On 05/09, Chao Yu wrote:
> On 2019/5/9 12:15, Jaegeuk Kim wrote:
> > On 04/11, 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()
> >>
> >> v4:
> >> * change boundry definition
> >>
> >> v5:
> >> * revise boundry definition
> >> ---
> >>  fs/f2fs/xattr.c | 32 +++++++++++++++++++++++++++-----
> >>  1 file changed, 27 insertions(+), 5 deletions(-)
> >>
> >> diff --git a/fs/f2fs/xattr.c b/fs/f2fs/xattr.c
> >> index 848a785abe25..587429e29a69 100644
> >> --- a/fs/f2fs/xattr.c
> >> +++ b/fs/f2fs/xattr.c
> >> @@ -202,12 +202,18 @@ 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,
> >> +				void *last_base_addr, int index,
> >> +				size_t len, const char *name)
> >>  {
> >>  	struct f2fs_xattr_entry *entry;
> >>  
> >>  	list_for_each_xattr(entry, base_addr) {
> >> +		if ((void *)(entry) + sizeof(__u32) > last_base_addr ||
> >> +			(void *)XATTR_NEXT_ENTRY(entry) +
> >> +			sizeof(__u32) > last_base_addr)
> >> +			return NULL;
> >> +
> >>  		if (entry->e_name_index != index)
> >>  			continue;
> >>  		if (entry->e_name_len != len)
> >> @@ -298,6 +304,7 @@ static int lookup_all_xattrs(struct inode *inode, struct page *ipage,
> >>  				void **base_addr, int *base_size)
> >>  {
> >>  	void *cur_addr, *txattr_addr, *last_addr = NULL;
> >> +	void *last_txattr_addr = NULL;
> >>  	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);
> >> @@ -311,6 +318,8 @@ static int lookup_all_xattrs(struct inode *inode, struct page *ipage,
> >>  	if (!txattr_addr)
> >>  		return -ENOMEM;
> >>  
> >> +	last_txattr_addr = (void *)txattr_addr + inline_size + size;
> > 
> > I just found this should be + XATTR_PADDING_SIZE. Otherwise, generic/026 fails.
> > Let me know, if there is any other concern below.
> 
> We're trying to use [txattr_addr, last_txattr_addr] to indicate valid range of
> xattr datas, any valid entries across the boundary is not allowed, so I think
> it's correct to exclude padding space for last_txattr_addr.

Okay, how about this?