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Subject[PATCH v5] f2fs: fix to avoid accessing xattr across the boundary
From
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@google.com>
---
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;
+
/* read from inline xattr */
if (inline_size) {
err = read_inline_xattr(inode, ipage, txattr_addr);
@@ -337,7 +346,11 @@ 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, last_txattr_addr, index, len, name);
+ if (!*xe) {
+ err = -EFAULT;
+ goto out;
+ }
check:
if (IS_XATTR_LAST_ENTRY(*xe)) {
err = -ENODATA;
@@ -581,10 +594,14 @@ static int __f2fs_setxattr(struct inode *inode, int index,
struct page *ipage, int flags)
{
struct f2fs_xattr_entry *here, *last;
- void *base_addr;
+ void *base_addr, *last_base_addr = NULL;
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);
+
int error = 0;

if (name == NULL)
@@ -604,9 +621,14 @@ static int __f2fs_setxattr(struct inode *inode, int index,
error = read_all_xattrs(inode, ipage, &base_addr);
if (error)
return error;
+ last_base_addr = (void *)base_addr + xattr_nid_size + inline_size;

/* find entry with wanted name. */
- here = __find_xattr(base_addr, index, len, name);
+ here = __find_xattr(base_addr, last_base_addr, index, len, name);
+ if (!here) {
+ error = -EFAULT;
+ goto exit;
+ }

found = IS_XATTR_LAST_ENTRY(here) ? 0 : 1;

--
2.21.0.392.gf8f6787159e-goog
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