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Date: Thu, 2 Jun 2022 19:46:51 +0800
From: Baokun Li <libaokun1@...wei.com>
To: <linux-ext4@...r.kernel.org>
CC: <tytso@....edu>, <adilger.kernel@...ger.ca>, <jack@...e.cz>,
<ritesh.list@...il.com>, <lczerner@...hat.com>,
<linux-kernel@...r.kernel.org>, <yi.zhang@...wei.com>,
<yebin10@...wei.com>, <yukuai3@...wei.com>, <libaokun1@...wei.com>,
Hulk Robot <hulkci@...wei.com>
Subject: [PATCH] ext4: fix use-after-free in ext4_xattr_set_entry
Hulk Robot reported a issue:
==================================================================
BUG: KASAN: use-after-free in ext4_xattr_set_entry+0x18ab/0x3500
Write of size 4105 at addr ffff8881675ef5f4 by task syz-executor.0/7092
CPU: 1 PID: 7092 Comm: syz-executor.0 Not tainted 4.19.90-dirty #17
Call Trace:
[...]
memcpy+0x34/0x50 mm/kasan/kasan.c:303
ext4_xattr_set_entry+0x18ab/0x3500 fs/ext4/xattr.c:1747
ext4_xattr_ibody_inline_set+0x86/0x2a0 fs/ext4/xattr.c:2205
ext4_xattr_set_handle+0x940/0x1300 fs/ext4/xattr.c:2386
ext4_xattr_set+0x1da/0x300 fs/ext4/xattr.c:2498
__vfs_setxattr+0x112/0x170 fs/xattr.c:149
__vfs_setxattr_noperm+0x11b/0x2a0 fs/xattr.c:180
__vfs_setxattr_locked+0x17b/0x250 fs/xattr.c:238
vfs_setxattr+0xed/0x270 fs/xattr.c:255
setxattr+0x235/0x330 fs/xattr.c:520
path_setxattr+0x176/0x190 fs/xattr.c:539
__do_sys_lsetxattr fs/xattr.c:561 [inline]
__se_sys_lsetxattr fs/xattr.c:557 [inline]
__x64_sys_lsetxattr+0xc2/0x160 fs/xattr.c:557
do_syscall_64+0xdf/0x530 arch/x86/entry/common.c:298
entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x459fe9
RSP: 002b:00007fa5e54b4c08 EFLAGS: 00000246 ORIG_RAX: 00000000000000bd
RAX: ffffffffffffffda RBX: 000000000051bf60 RCX: 0000000000459fe9
RDX: 00000000200003c0 RSI: 0000000020000180 RDI: 0000000020000140
RBP: 000000000051bf60 R08: 0000000000000001 R09: 0000000000000000
R10: 0000000000001009 R11: 0000000000000246 R12: 0000000000000000
R13: 00007ffc73c93fc0 R14: 000000000051bf60 R15: 00007fa5e54b4d80
[...]
==================================================================
Above issue may happen as follows:
-------------------------------------
ext4_xattr_set
ext4_xattr_set_handle
ext4_xattr_ibody_find
>> s->end < s->base
>> no EXT4_STATE_XATTR
>> xattr_check_inode is not executed
ext4_xattr_ibody_set
ext4_xattr_set_entry
>> size_t min_offs = s->end - s->base
>> UAF in memcpy
we can easily reproduce this problem with the following commands:
mkfs.ext4 -F /dev/sda
mount -o debug_want_extra_isize=128 /dev/sda /mnt
touch /mnt/file
setfattr -n user.cat -v `seq -s z 4096|tr -d '[:digit:]'` /mnt/file
In ext4_xattr_ibody_find, we have the following assignment logic:
header = IHDR(inode, raw_inode)
= raw_inode + EXT4_GOOD_OLD_INODE_SIZE + i_extra_isize
is->s.base = IFIRST(header)
= header + sizeof(struct ext4_xattr_ibody_header)
is->s.end = raw_inode + s_inode_size
Obviously, when the inode does not have EXT4_status_XATTR and its
i_extra_isize is large, is->s.end may be larger than is->s.base.
In this case, the above issue may be triggered.
EXT4_GOOD_OLD_INODE_SIZE extra_isize header entry pad data
|---------------------------|------------|------|---------|---|--------|
As shown above, when adding an xattr to an inode, we must ensure that the
inode_size is not less than EXT4_GOOD_OLD_INODE_SIZE + extra_isize + pad.
Reported-by: Hulk Robot <hulkci@...wei.com>
Signed-off-by: Baokun Li <libaokun1@...wei.com>
---
fs/ext4/inline.c | 3 +++
fs/ext4/inode.c | 3 +--
fs/ext4/xattr.c | 6 ++++--
fs/ext4/xattr.h | 6 ++++++
4 files changed, 14 insertions(+), 4 deletions(-)
diff --git a/fs/ext4/inline.c b/fs/ext4/inline.c
index cff52ff6549d..b8cec7cb4b08 100644
--- a/fs/ext4/inline.c
+++ b/fs/ext4/inline.c
@@ -35,6 +35,9 @@ static int get_max_inline_xattr_value_size(struct inode *inode,
struct ext4_inode *raw_inode;
int free, min_offs;
+ if (!INODE_HAVE_XATTR_SPACE(inode))
+ return 0;
+
min_offs = EXT4_SB(inode->i_sb)->s_inode_size -
EXT4_GOOD_OLD_INODE_SIZE -
EXT4_I(inode)->i_extra_isize -
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 3dce7d058985..714fa61d0afb 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -4685,8 +4685,7 @@ static inline int ext4_iget_extra_inode(struct inode *inode,
__le32 *magic = (void *)raw_inode +
EXT4_GOOD_OLD_INODE_SIZE + ei->i_extra_isize;
- if (EXT4_GOOD_OLD_INODE_SIZE + ei->i_extra_isize + sizeof(__le32) <=
- EXT4_INODE_SIZE(inode->i_sb) &&
+ if (INODE_HAVE_XATTR_SPACE(inode) &&
*magic == cpu_to_le32(EXT4_XATTR_MAGIC)) {
ext4_set_inode_state(inode, EXT4_STATE_XATTR);
return ext4_find_inline_data_nolock(inode);
diff --git a/fs/ext4/xattr.c b/fs/ext4/xattr.c
index 042325349098..4a63f8386910 100644
--- a/fs/ext4/xattr.c
+++ b/fs/ext4/xattr.c
@@ -2176,8 +2176,9 @@ int ext4_xattr_ibody_find(struct inode *inode, struct ext4_xattr_info *i,
struct ext4_inode *raw_inode;
int error;
- if (EXT4_I(inode)->i_extra_isize == 0)
+ if (!INODE_HAVE_XATTR_SPACE(inode))
return 0;
+
raw_inode = ext4_raw_inode(&is->iloc);
header = IHDR(inode, raw_inode);
is->s.base = is->s.first = IFIRST(header);
@@ -2205,8 +2206,9 @@ int ext4_xattr_ibody_set(handle_t *handle, struct inode *inode,
struct ext4_xattr_search *s = &is->s;
int error;
- if (EXT4_I(inode)->i_extra_isize == 0)
+ if (!INODE_HAVE_XATTR_SPACE(inode))
return -ENOSPC;
+
error = ext4_xattr_set_entry(i, s, handle, inode, false /* is_block */);
if (error)
return error;
diff --git a/fs/ext4/xattr.h b/fs/ext4/xattr.h
index 77efb9a627ad..f2b299b347f9 100644
--- a/fs/ext4/xattr.h
+++ b/fs/ext4/xattr.h
@@ -95,6 +95,12 @@ struct ext4_xattr_entry {
#define EXT4_ZERO_XATTR_VALUE ((void *)-1)
+#define INODE_HAVE_XATTR_SPACE(inode) \
+ ((EXT4_I(inode)->i_extra_isize != 0) && \
+ (EXT4_GOOD_OLD_INODE_SIZE + EXT4_I(inode)->i_extra_isize + \
+ sizeof(struct ext4_xattr_ibody_header) + EXT4_XATTR_PAD <= \
+ EXT4_INODE_SIZE((inode)->i_sb)))
+
struct ext4_xattr_info {
const char *name;
const void *value;
--
2.31.1
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