[syzbot] general protection fault in ovl_dentry_upper

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: fe24a97cf254 Merge tag 'input-for-v6.1-rc5' of git://git.k..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=15a02765880000
kernel config: https://syzkaller.appspot.com/x/.config?x=6f9416d398342c83
dashboard link: https://syzkaller.appspot.com/bug?extid=a4055c78774bbf3498bb
compiler: Debian clang version 13.0.1-++20220126092033+75e33f71c2da-1~exp1~20220126212112.63, GNU ld (GNU Binutils for Debian) 2.35.2
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=10a320fd880000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=10e6b6ed880000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/d4424ef25058/disk-fe24a97c.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/61c4ed6a96dd/vmlinux-fe24a97c.xz
kernel image: https://storage.googleapis.com/syzbot-assets/d1b8ff061e4e/bzImage-fe24a97c.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+a4055c...@syzkaller.appspotmail.com

general protection fault, probably for non-canonical address 0xdffffc0000000092: 0000 [#1] PREEMPT SMP KASAN
KASAN: null-ptr-deref in range [0x0000000000000490-0x0000000000000497]
CPU: 0 PID: 16299 Comm: syz-executor309 Not tainted 6.1.0-rc5-syzkaller-00307-gfe24a97cf254 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/26/2022
RIP: 0010:ovl_upperdentry_dereference fs/overlayfs/ovl_entry.h:150 [inline]
RIP: 0010:ovl_dentry_upper+0x40/0x60 fs/overlayfs/util.c:213
Code: fe 49 83 c6 68 4c 89 f0 48 c1 e8 03 42 80 3c 38 00 74 08 4c 89 f7 e8 7f 28 e9 fe bb 90 04 00 00 49 03 1e 48 89 d8 48 c1 e8 03 <42> 80 3c 38 00 74 08 48 89 df e8 61 28 e9 fe 48 8b 03 5b 41 5e 41
RSP: 0018:ffffc9000ef3fa50 EFLAGS: 00010202
RAX: 0000000000000092 RBX: 0000000000000490 RCX: ffff888020328000
RDX: 0000000000000000 RSI: 0000000000000040 RDI: ffff888075528758
RBP: dffffc0000000000 R08: ffffffff81f2119e R09: ffffed100eaa50fa
R10: ffffed100eaa50fa R11: 1ffff1100eaa50f9 R12: 0000000000000040
R13: ffffc9000ef3fc20 R14: ffff8880755287c0 R15: dffffc0000000000
FS: 00007f7e44d61700(0000) GS:ffff8880b9800000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f7e44df1800 CR3: 000000007c404000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
<TASK>
ovl_dentry_revalidate_common fs/overlayfs/super.c:146 [inline]
ovl_dentry_revalidate+0x4b/0x380 fs/overlayfs/super.c:159
d_revalidate fs/namei.c:856 [inline]
lookup_fast+0x26c/0x480 fs/namei.c:1634
walk_component+0x55/0x410 fs/namei.c:1989
lookup_last fs/namei.c:2450 [inline]
path_lookupat+0x17d/0x450 fs/namei.c:2474
filename_lookup+0x274/0x650 fs/namei.c:2503
user_path_at_empty+0x40/0x1a0 fs/namei.c:2876
user_path_at include/linux/namei.h:57 [inline]
__do_sys_name_to_handle_at fs/fhandle.c:107 [inline]
__se_sys_name_to_handle_at+0xf8/0x610 fs/fhandle.c:93
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x3d/0xb0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x63/0xcd
RIP: 0033:0x7f7e44db0159
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 41 15 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:00007f7e44d612f8 EFLAGS: 00000246 ORIG_RAX: 000000000000012f
RAX: ffffffffffffffda RBX: 0000000000000034 RCX: 00007f7e44db0159
RDX: 0000000000000000 RSI: 0000000020000100 RDI: 0000000000000003
RBP: 00007f7e44e394a8 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f7e44e394a0
R13: 00007f7e44e394ac R14: 00007f7e44e06074 R15: 0030656c69662f2e
</TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:ovl_upperdentry_dereference fs/overlayfs/ovl_entry.h:150 [inline]
RIP: 0010:ovl_dentry_upper+0x40/0x60 fs/overlayfs/util.c:213
Code: fe 49 83 c6 68 4c 89 f0 48 c1 e8 03 42 80 3c 38 00 74 08 4c 89 f7 e8 7f 28 e9 fe bb 90 04 00 00 49 03 1e 48 89 d8 48 c1 e8 03 <42> 80 3c 38 00 74 08 48 89 df e8 61 28 e9 fe 48 8b 03 5b 41 5e 41
RSP: 0018:ffffc9000ef3fa50 EFLAGS: 00010202
RAX: 0000000000000092 RBX: 0000000000000490 RCX: ffff888020328000
RDX: 0000000000000000 RSI: 0000000000000040 RDI: ffff888075528758
RBP: dffffc0000000000 R08: ffffffff81f2119e R09: ffffed100eaa50fa
R10: ffffed100eaa50fa R11: 1ffff1100eaa50f9 R12: 0000000000000040
R13: ffffc9000ef3fc20 R14: ffff8880755287c0 R15: dffffc0000000000
FS: 00007f7e44d61700(0000) GS:ffff8880b9800000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000564e6292d008 CR3: 000000007c404000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
----------------
Code disassembly (best guess), 1 bytes skipped:
0: 49 83 c6 68 add $0x68,%r14
4: 4c 89 f0 mov %r14,%rax
7: 48 c1 e8 03 shr $0x3,%rax
b: 42 80 3c 38 00 cmpb $0x0,(%rax,%r15,1)
10: 74 08 je 0x1a
12: 4c 89 f7 mov %r14,%rdi
15: e8 7f 28 e9 fe callq 0xfee92899
1a: bb 90 04 00 00 mov $0x490,%ebx
1f: 49 03 1e add (%r14),%rbx
22: 48 89 d8 mov %rbx,%rax
25: 48 c1 e8 03 shr $0x3,%rax
* 29: 42 80 3c 38 00 cmpb $0x0,(%rax,%r15,1) <-- trapping instruction
2e: 74 08 je 0x38
30: 48 89 df mov %rbx,%rdi
33: e8 61 28 e9 fe callq 0xfee92899
38: 48 8b 03 mov (%rbx),%rax
3b: 5b pop %rbx
3c: 41 5e pop %r14
3e: 41 rex.B


---
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[陈中津]

derefrence inode directly under rcu-walk mode.

#syz test https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git fe24a97cf2543e8832e7a2124802e5c32aac05aa

--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -139,11 +139,19 @@ static int ovl_dentry_revalidate_common(struct dentry *dentry,
                                        unsigned int flags, bool weak)
 {
        struct ovl_entry *oe = dentry->d_fsdata;
+       struct inode *inode;
        struct dentry *upper;
        unsigned int i;
        int ret = 1;

-       upper = ovl_dentry_upper(dentry);
+       if (flags & LOOKUP_RCU) {
+               inode = d_inode_rcu(dentry);
+               if (!inode)
+                       return -ECHILD;
+               upper = ovl_upperdentry_dereference(OVL_I(inode));
+       } else
+               upper = ovl_dentry_upper(dentry);
+
        if (upper)
                ret = ovl_revalidate_real(upper, flags, weak);

[Miklos Szeredi]

#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
master

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-and-tested-by: syzbot+a4055c...@syzkaller.appspotmail.com

Tested on:

commit: c3eb11fb Merge tag 'pci-v6.1-fixes-3' of git://git.ker..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=14a0ec05880000
kernel config: https://syzkaller.appspot.com/x/.config?x=8cdf448d3b35234

dashboard link: https://syzkaller.appspot.com/bug?extid=a4055c78774bbf3498bb
compiler: Debian clang version 13.0.1-++20220126092033+75e33f71c2da-1~exp1~20220126212112.63, GNU ld (GNU Binutils for Debian) 2.35.2

patch: https://syzkaller.appspot.com/x/patch.diff?x=16b17403880000

Note: testing is done by a robot and is best-effort only.