On Fri 07-02-25 17:31:49, yebin wrote:
> On 2025/2/7 12:16, Darrick J. Wong wrote:
> > On Fri, Feb 07, 2025 at 11:27:43AM +0800, Ye Bin wrote:
> > > From: Ye Bin <yebin10@xxxxxxxxxx>
> > >
> > > There's issue as follows:
> > > BUG: KASAN: use-after-free in ext4_xattr_inode_dec_ref_all+0x6ff/0x790
> > > Read of size 4 at addr ffff88807b003000 by task syz-executor.0/15172
> > >
> > > CPU: 3 PID: 15172 Comm: syz-executor.0
> > > Call Trace:
> > > __dump_stack lib/dump_stack.c:82 [inline]
> > > dump_stack+0xbe/0xfd lib/dump_stack.c:123
> > > print_address_description.constprop.0+0x1e/0x280 mm/kasan/report.c:400
> > > __kasan_report.cold+0x6c/0x84 mm/kasan/report.c:560
> > > kasan_report+0x3a/0x50 mm/kasan/report.c:585
> > > ext4_xattr_inode_dec_ref_all+0x6ff/0x790 fs/ext4/xattr.c:1137
> > > ext4_xattr_delete_inode+0x4c7/0xda0 fs/ext4/xattr.c:2896
> > > ext4_evict_inode+0xb3b/0x1670 fs/ext4/inode.c:323
> > > evict+0x39f/0x880 fs/inode.c:622
> > > iput_final fs/inode.c:1746 [inline]
> > > iput fs/inode.c:1772 [inline]
> > > iput+0x525/0x6c0 fs/inode.c:1758
> > > ext4_orphan_cleanup fs/ext4/super.c:3298 [inline]
> > > ext4_fill_super+0x8c57/0xba40 fs/ext4/super.c:5300
> > > mount_bdev+0x355/0x410 fs/super.c:1446
> > > legacy_get_tree+0xfe/0x220 fs/fs_context.c:611
> > > vfs_get_tree+0x8d/0x2f0 fs/super.c:1576
> > > do_new_mount fs/namespace.c:2983 [inline]
> > > path_mount+0x119a/0x1ad0 fs/namespace.c:3316
> > > do_mount+0xfc/0x110 fs/namespace.c:3329
> > > __do_sys_mount fs/namespace.c:3540 [inline]
> > > __se_sys_mount+0x219/0x2e0 fs/namespace.c:3514
> > > do_syscall_64+0x33/0x40 arch/x86/entry/common.c:46
> > > entry_SYSCALL_64_after_hwframe+0x67/0xd1
> > >
> > > Memory state around the buggy address:
> > > ffff88807b002f00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> > > ffff88807b002f80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> > > > ffff88807b003000: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
> > > ^
> > > ffff88807b003080: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
> > > ffff88807b003100: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
> > >
> > > Above issue happens as ext4_xattr_delete_inode() isn't check xattr
> > > is valid if xattr is in inode.
> > > To solve above issue call xattr_check_inode() check if xattr if valid
> > > in inode.
> > >
> > > Fixes: e50e5129f384 ("ext4: xattr-in-inode support")
> > > Signed-off-by: Ye Bin <yebin10@xxxxxxxxxx>
> > > ---
> > > fs/ext4/xattr.c | 14 +++++++++++---
> > > 1 file changed, 11 insertions(+), 3 deletions(-)
> > >
> > > diff --git a/fs/ext4/xattr.c b/fs/ext4/xattr.c
> > > index 0e4494863d15..cb724477f8da 100644
> > > --- a/fs/ext4/xattr.c
> > > +++ b/fs/ext4/xattr.c
> > > @@ -2922,7 +2922,6 @@ int ext4_xattr_delete_inode(handle_t *handle, struct inode *inode,
> > > int extra_credits)
> > > {
> > > struct buffer_head *bh = NULL;
> > > - struct ext4_xattr_ibody_header *header;
> > > struct ext4_iloc iloc = { .bh = NULL };
> > > struct ext4_xattr_entry *entry;
> > > struct inode *ea_inode;
> > > @@ -2937,6 +2936,9 @@ int ext4_xattr_delete_inode(handle_t *handle, struct inode *inode,
> > >
> > > if (ext4_has_feature_ea_inode(inode->i_sb) &&
> > > ext4_test_inode_state(inode, EXT4_STATE_XATTR)) {
> > > + struct ext4_xattr_ibody_header *header;
> > > + struct ext4_inode *raw_inode;
> > > + void *end;
> > >
> > > error = ext4_get_inode_loc(inode, &iloc);
> > > if (error) {
> > > @@ -2952,14 +2954,20 @@ int ext4_xattr_delete_inode(handle_t *handle, struct inode *inode,
> > > goto cleanup;
> > > }
> > >
> > > - header = IHDR(inode, ext4_raw_inode(&iloc));
> > > - if (header->h_magic == cpu_to_le32(EXT4_XATTR_MAGIC))
> > > + raw_inode = ext4_raw_inode(&iloc);
> > > + header = IHDR(inode, raw_inode);
> > > + end = ITAIL(inode, raw_inode);
> > > + if (header->h_magic == cpu_to_le32(EXT4_XATTR_MAGIC)) {
> >
> > This needs to make sure that header + sizeof(h_magic) >= end before
> > checking the magic number in header::h_magic, right?
> >
> > --D
> Thank you for your reply.
> There ' s no need to check "header + sizeof(h_magic) >= end" because it has
> been checked
> when the EXT4_STATE_XATTR flag bit is set:
> __ext4_iget
> ret = ext4_iget_extra_inode(inode, raw_inode, ei);
> if (EXT4_INODE_HAS_XATTR_SPACE(inode) && *magic ==
> cpu_to_le32(EXT4_XATTR_MAGIC))
> ext4_set_inode_state(inode, EXT4_STATE_XATTR);
> It seems that the judgment of "header->h_magic ==
> cpu_to_le32(EXT4_XATTR_MAGIC)"
> should be redundant here.
Yes, if we have EXT4_STATE_XATTR set, xattr_check_inode() should be safe to
call (ext4_iget_extra_inode() makes sure inode space is sane) and should
return success. I'm actually wondering whether it wouldn't be better for
ext4_iget_extra_inode() to check xattr validity with xattr_check_inode()
along with setting EXT4_STATE_XATTR. So we'd be checking xattr validity
when loading from disk similarly as for xattr blocks which is a well
defined place. When doing the checking on use (as we do now) it is always
easy to miss some place...
Honza
> > > + error = xattr_check_inode(inode, header, end);
> > > + if (error)
> > > + goto cleanup;
> > > ext4_xattr_inode_dec_ref_all(handle, inode, iloc.bh,
> > > IFIRST(header),
> > > false /* block_csum */,
> > > ea_inode_array,
> > > extra_credits,
> > > false /* skip_quota */);
> > > + }
> > > }
> > >
> > > if (EXT4_I(inode)->i_file_acl) {
> > > --
> > > 2.34.1
> > >
> > >
> >
>
--
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR
