linux-kernel - [PATCH] f2fs: fix to avoid accessing xattr across the boundary

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Date:   Mon,  8 Apr 2019 16:50:16 +0800
From:   Randall Huang <huangrandall@...gle.com>
To:     jaegeuk@...nel.org, yuchao0@...wei.com,
        linux-f2fs-devel@...ts.sourceforge.net,
        linux-kernel@...r.kernel.org
Cc:     huangrandall@...gle.com
Subject: [PATCH] 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

Bug: 126558260

Signed-off-by: Randall Huang <huangrandall@...gle.com>
---
 fs/f2fs/xattr.c | 22 ++++++++++++++++------
 1 file changed, 16 insertions(+), 6 deletions(-)

diff --git a/fs/f2fs/xattr.c b/fs/f2fs/xattr.c
index 848a785abe25..0531c1e38275 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,
+				int base_addr_limit, int index,
+				size_t len, const char *name)
 {
 	struct f2fs_xattr_entry *entry;
+	void *max_addr = base_addr + ENTRY_SIZE(XATTR_ENTRY(base_addr)) +
+		base_addr_limit - 1;
 
 	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)
@@ -337,9 +342,9 @@ 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, XATTR_PADDING_SIZE, index, len, name);
 check:
-	if (IS_XATTR_LAST_ENTRY(*xe)) {
+	if (!*xe || IS_XATTR_LAST_ENTRY(*xe)) {
 		err = -ENODATA;
 		goto out;
 	}
@@ -606,9 +611,14 @@ 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, inline_xattr_size(inode) +
+			VALID_XATTR_BLOCK_SIZE + XATTR_PADDING_SIZE,
+			index, len, name);
 
-	found = IS_XATTR_LAST_ENTRY(here) ? 0 : 1;
+	if (!here)
+		found = 0;
+	else
+		found = IS_XATTR_LAST_ENTRY(here) ? 0 : 1;
 
 	if (found) {
 		if ((flags & XATTR_CREATE)) {
-- 
2.21.0.392.gf8f6787159e-goog