| Message ID | 20241122081025.1661161-1-lizhi.xu@windriver.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | [V4] fs/ntfs3: check if the inode is bad before creating symlink | expand |
On Fri 22-11-24 16:10:25, Lizhi Xu wrote: > syzbot reported a null-ptr-deref in pick_link. [1] > > First, i_link and i_dir_seq are in the same union, they share the same memory > address, and i_dir_seq will be updated during the execution of walk_component, > which makes the value of i_link equal to i_dir_seq. > > Secondly, the chmod execution failed, which resulted in setting the mode value > of file0's inode to REG when executing ntfs_bad_inode. > > Third, during the execution of the link command, it sets the inode of the > symlink file to the already bad inode of file0 by calling d_instantiate, which > ultimately leads to null-ptr-deref when performing a mount operation on the > symbolic link bus because it use bad inode's i_link and its value is equal to > i_dir_seq=2. > > Note: ("file0, bus" are defined in reproducer [2]) > > To avoid null-ptr-deref in pick_link, when creating a symbolic link, first check > whether the inode of file is already bad. So actually there's no symbolic link involved here at all (which what was confusing me all the time). > move_mount(0xffffffffffffff9c, &(0x7f00000003c0)='./file0\x00', 0xffffffffffffff9c, &(0x7f0000000400)='./file0/file0\x00', 0x140) > chmod(&(0x7f0000000080)='./file0\x00', 0x0) > link(&(0x7f0000000200)='./file0\x00', &(0x7f0000000240)='./bus\x00') > mount$overlay(0x0, &(0x7f00000000c0)='./bus\x00', 0x0, 0x0, 0x0) This creates only a hardlink. And in fact the creation of the link seems to be totally irrelevant for this problem. I believe: move_mount(0xffffffffffffff9c, &(0x7f00000003c0)='./file0\x00', 0xffffffffffffff9c, &(0x7f0000000400)='./file0/file0\x00', 0x140) chmod(&(0x7f0000000080)='./file0\x00', 0x0) mount$overlay(0x0, &(0x7f00000000c0)='./file0\x00', 0x0, 0x0, 0x0) would be as good reproducer of the problem. The core of the problem is that NTFS3 calls make_bad_inode() on inode that is accessible to userspace and is something else than a regular file. As long as that happens, some variant of this NULL-ptr-dereference can happen as well, just the reproducers will be somewhat different. So I don't think patching ntfs_link_inode() makes a lot of sense. If anything, I'd patch NTFS3 to not mark the inode as bad somewhere inside ntfs_setattr() and deal with the error in a better way. Honza > > Reported-by: syzbot+73d8fc29ec7cba8286fa@syzkaller.appspotmail.com > Closes: https://syzkaller.appspot.com/bug?extid=73d8fc29ec7cba8286fa > Signed-off-by: Lizhi Xu <lizhi.xu@windriver.com> > --- > V1 --> V2: add the root cause of the i_link not set issue and imporve the check > V2 --> V3: when creating a symbolic link, first check whether the inode of file is bad. > V3 --> V4: add comments for symlink use bad inode, it is the root cause > > fs/ntfs3/inode.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/fs/ntfs3/inode.c b/fs/ntfs3/inode.c > index be04d2845bb7..fefbdcf75016 100644 > --- a/fs/ntfs3/inode.c > +++ b/fs/ntfs3/inode.c > @@ -1719,6 +1719,9 @@ int ntfs_link_inode(struct inode *inode, struct dentry *dentry) > struct ntfs_sb_info *sbi = inode->i_sb->s_fs_info; > struct NTFS_DE *de; > > + if (is_bad_inode(inode)) > + return -EIO; > + > /* Allocate PATH_MAX bytes. */ > de = __getname(); > if (!de) > -- > 2.43.0 >
diff --git a/fs/ntfs3/inode.c b/fs/ntfs3/inode.c index be04d2845bb7..fefbdcf75016 100644 --- a/fs/ntfs3/inode.c +++ b/fs/ntfs3/inode.c @@ -1719,6 +1719,9 @@ int ntfs_link_inode(struct inode *inode, struct dentry *dentry) struct ntfs_sb_info *sbi = inode->i_sb->s_fs_info; struct NTFS_DE *de; + if (is_bad_inode(inode)) + return -EIO; + /* Allocate PATH_MAX bytes. */ de = __getname(); if (!de)
syzbot reported a null-ptr-deref in pick_link. [1] First, i_link and i_dir_seq are in the same union, they share the same memory address, and i_dir_seq will be updated during the execution of walk_component, which makes the value of i_link equal to i_dir_seq. Secondly, the chmod execution failed, which resulted in setting the mode value of file0's inode to REG when executing ntfs_bad_inode. Third, during the execution of the link command, it sets the inode of the symlink file to the already bad inode of file0 by calling d_instantiate, which ultimately leads to null-ptr-deref when performing a mount operation on the symbolic link bus because it use bad inode's i_link and its value is equal to i_dir_seq=2. Note: ("file0, bus" are defined in reproducer [2]) To avoid null-ptr-deref in pick_link, when creating a symbolic link, first check whether the inode of file is already bad. [1] KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007] CPU: 0 UID: 0 PID: 5310 Comm: syz-executor255 Not tainted 6.12.0-rc6-syzkaller-00318-ga9cda7c0ffed #0 Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014 RIP: 0010:pick_link+0x51c/0xd50 fs/namei.c:1864 Code: c1 e8 03 42 80 3c 38 00 74 08 48 89 df e8 fc 00 e9 ff 48 8b 2b 48 85 ed 0f 84 92 00 00 00 e8 7b 36 7f ff 48 89 e8 48 c1 e8 03 <42> 0f b6 04 38 84 c0 0f 85 a2 05 00 00 0f b6 5d 00 bf 2f 00 00 00 RSP: 0018:ffffc9000d147998 EFLAGS: 00010246 RAX: 0000000000000000 RBX: ffff88804558dec8 RCX: ffff88801ec7a440 RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000 RBP: 0000000000000002 R08: ffffffff8215a35f R09: 1ffffffff203a13d R10: dffffc0000000000 R11: fffffbfff203a13e R12: 1ffff92001a28f93 R13: ffffc9000d147af8 R14: 1ffff92001a28f5f R15: dffffc0000000000 FS: 0000555577611380(0000) GS:ffff88801fc00000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007fcc0a595ed8 CR3: 0000000035760000 CR4: 0000000000352ef0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 Call Trace: <TASK> step_into+0xca9/0x1080 fs/namei.c:1923 lookup_last fs/namei.c:2556 [inline] path_lookupat+0x16f/0x450 fs/namei.c:2580 filename_lookup+0x256/0x610 fs/namei.c:2609 user_path_at+0x3a/0x60 fs/namei.c:3016 do_mount fs/namespace.c:3844 [inline] __do_sys_mount fs/namespace.c:4057 [inline] __se_sys_mount+0x297/0x3c0 fs/namespace.c:4034 do_syscall_x64 arch/x86/entry/common.c:52 [inline] do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83 entry_SYSCALL_64_after_hwframe+0x77/0x7f RIP: 0033:0x7f4b18ad5b19 Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 f1 17 00 00 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 b8 ff ff ff f7 d8 64 89 01 48 RSP: 002b:00007ffc2e486c48 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5 RAX: ffffffffffffffda RBX: 0030656c69662f2e RCX: 00007f4b18ad5b19 RDX: 0000000000000000 RSI: 00000000200000c0 RDI: 0000000000000000 RBP: 00007f4b18b685f0 R08: 0000000000000000 R09: 00005555776124c0 R10: 0000000000000000 R11: 0000000000000246 R12: 00007ffc2e486c70 R13: 00007ffc2e486e98 R14: 431bde82d7b634db R15: 00007f4b18b1e03b </TASK> [2] move_mount(0xffffffffffffff9c, &(0x7f00000003c0)='./file0\x00', 0xffffffffffffff9c, &(0x7f0000000400)='./file0/file0\x00', 0x140) chmod(&(0x7f0000000080)='./file0\x00', 0x0) link(&(0x7f0000000200)='./file0\x00', &(0x7f0000000240)='./bus\x00') mount$overlay(0x0, &(0x7f00000000c0)='./bus\x00', 0x0, 0x0, 0x0) Reported-by: syzbot+73d8fc29ec7cba8286fa@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=73d8fc29ec7cba8286fa Signed-off-by: Lizhi Xu <lizhi.xu@windriver.com> --- V1 --> V2: add the root cause of the i_link not set issue and imporve the check V2 --> V3: when creating a symbolic link, first check whether the inode of file is bad. V3 --> V4: add comments for symlink use bad inode, it is the root cause fs/ntfs3/inode.c | 3 +++ 1 file changed, 3 insertions(+)