f2fs: fix to avoid accessing xattr across the boundary

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

Signed-off-by: Randall Huang <huangrandall@google.com>
[Jaegeuk Kim: Fix wrong ending boundary]
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

2 files changed, 29 insertions, 9 deletions

diff --git a/fs/f2fs/xattr.c b/fs/f2fs/xattr.c
index 848a785abe25..e791741d193b 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,
+                                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) > last_base_addr)
+                        return NULL;
+
                 if (entry->e_name_index != index)
                         continue;
                 if (entry->e_name_len != len)
@@ -297,20 +302,22 @@ static int lookup_all_xattrs(struct inode *inode, struct page *ipage,
                                 const char *name, struct f2fs_xattr_entry **xe,
                                 void **base_addr, int *base_size)
 {
-        void *cur_addr, *txattr_addr, *last_addr = NULL;
+        void *cur_addr, *txattr_addr, *last_txattr_addr;
+        void *last_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);
         int err = 0;
 
-        if (!size && !inline_size)
+        if (!xnid && !inline_size)
                 return -ENODATA;
 
-        *base_size = inline_size + size + XATTR_PADDING_SIZE;
+        *base_size = XATTR_SIZE(xnid, inode) + XATTR_PADDING_SIZE;
         txattr_addr = f2fs_kzalloc(F2FS_I_SB(inode), *base_size, GFP_NOFS);
         if (!txattr_addr)
                 return -ENOMEM;
 
+        last_txattr_addr = (void *)txattr_addr + XATTR_SIZE(xnid, inode);
+
         /* read from inline xattr */
         if (inline_size) {
                 err = read_inline_xattr(inode, ipage, txattr_addr);
@@ -337,7 +344,11 @@ 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;
@@ -581,7 +592,8 @@ 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;
+        nid_t xnid = F2FS_I(inode)->i_xattr_nid;
         int found, newsize;
         size_t len;
         __u32 new_hsize;
@@ -605,8 +617,14 @@ static int __f2fs_setxattr(struct inode *inode, int index,
         if (error)
                 return error;
 
+        last_base_addr = (void *)base_addr + XATTR_SIZE(xnid, inode);
+
         /* 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;
 
diff --git a/fs/f2fs/xattr.h b/fs/f2fs/xattr.h
index 9172ee082ca8..a90920e2f949 100644
--- a/fs/f2fs/xattr.h
+++ b/fs/f2fs/xattr.h
@@ -71,6 +71,8 @@ struct f2fs_xattr_entry {
                                 entry = XATTR_NEXT_ENTRY(entry))
 #define VALID_XATTR_BLOCK_SIZE  (PAGE_SIZE - sizeof(struct node_footer))
 #define XATTR_PADDING_SIZE      (sizeof(__u32))
+#define XATTR_SIZE(x,i)         (((x) ? VALID_XATTR_BLOCK_SIZE : 0) +   \
+                                                (inline_xattr_size(i)))
 #define MIN_OFFSET(i)           XATTR_ALIGN(inline_xattr_size(i) +      \
                                                 VALID_XATTR_BLOCK_SIZE)