general protection fault in make_kuid

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: 6d21a41b Add linux-next specific files for 20190718
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=15200158600000
kernel config: https://syzkaller.appspot.com/x/.config?x=3430a151e1452331
dashboard link: https://syzkaller.appspot.com/bug?extid=7d6a57304857423318a5
compiler: gcc (GCC) 9.0.0 20181231 (experimental)
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1688da20600000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=16de4894600000

The bug was bisected to:

commit e786741ff1b52769b044b7f4407f39cd13ee5d2d
Author: Linus Torvalds <torv...@linux-foundation.org>
Date: Thu Jul 11 22:36:02 2019 +0000

Merge tag 'staging-5.3-rc1' of
git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/staging

bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=16610cf0600000
final crash: https://syzkaller.appspot.com/x/report.txt?x=15610cf0600000
console output: https://syzkaller.appspot.com/x/log.txt?x=11610cf0600000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+7d6a57...@syzkaller.appspotmail.com
Fixes: e786741ff1b5 ("Merge tag 'staging-5.3-rc1' of
git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/staging")

kasan: CONFIG_KASAN_INLINE enabled
kasan: GPF could be caused by NULL-ptr deref or user memory access
general protection fault: 0000 [#1] PREEMPT SMP KASAN
CPU: 0 PID: 9000 Comm: syz-executor213 Not tainted 5.2.0-next-20190718 #41
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
RIP: 0010:map_id_range_down+0x87/0x370 /kernel/user_namespace.c:293
Code: 6e 81 c7 00 f1 f1 f1 f1 c7 40 04 00 04 f3 f3 65 48 8b 04 25 28 00 00
00 48 89 45 d0 31 c0 e8 c0 a5 03 00 4c 89 f8 48 c1 e8 03 <42> 0f b6 04 28
84 c0 74 08 3c 03 0f 8e 9f 02 00 00 4c 8b ad 68 ff
RSP: 0018:ffff88809a567a30 EFLAGS: 00010246
RAX: 0000000000000000 RBX: ffff88809a567aa8 RCX: ffffffff825b97b5
RDX: 0000000000000000 RSI: ffffffff816edf30 RDI: 0000000000000000
RBP: ffff88809a567ad0 R08: ffff88808e4d2600 R09: ffffed1014af1713
R10: ffffed1014af1712 R11: 0000000000000003 R12: 0000000000000001
R13: dffffc0000000000 R14: 0000000000000000 R15: 0000000000000000
FS: 0000555555618880(0000) GS:ffff8880ae800000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000020000084 CR3: 000000008b2ec000 CR4: 00000000001406f0
Call Trace:
map_id_down /kernel/user_namespace.c:312 [inline]
make_kuid+0x23/0x30 /kernel/user_namespace.c:389
fuse_parse_param+0x2cb/0x750 /fs/fuse/inode.c:523
vfs_parse_fs_param+0x2ca/0x540 /fs/fs_context.c:145
vfs_parse_fs_string+0x105/0x170 /fs/fs_context.c:188
generic_parse_monolithic+0x181/0x200 /fs/fs_context.c:228
parse_monolithic_mount_data+0x69/0x90 /fs/fs_context.c:708
do_remount /fs/namespace.c:2520 [inline]
do_mount+0x924/0x1c30 /fs/namespace.c:3102
ksys_mount+0xdb/0x150 /fs/namespace.c:3320
__do_sys_mount /fs/namespace.c:3334 [inline]
__se_sys_mount /fs/namespace.c:3331 [inline]
__x64_sys_mount+0xbe/0x150 /fs/namespace.c:3331
do_syscall_64+0xfd/0x6a0 /arch/x86/entry/common.c:296
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x4406e9
Code: 18 89 d0 c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 00 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 0f 83 5b 14 fc ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007ffdf71f73c8 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 0000000000007275 RCX: 00000000004406e9
RDX: 0000000000000000 RSI: 0000000020000100 RDI: 0000000000000000
RBP: 00000000006cb018 R08: 0000000020000300 R09: 65732f636f72702f
R10: 0000000000000070 R11: 0000000000000246 R12: 0000000000401fd0
R13: 0000000000402060 R14: 0000000000000000 R15: 0000000000000000
Modules linked in:
---[ end trace 4fbbc963024437d2 ]---
RIP: 0010:map_id_range_down+0x87/0x370 /kernel/user_namespace.c:293
Code: 6e 81 c7 00 f1 f1 f1 f1 c7 40 04 00 04 f3 f3 65 48 8b 04 25 28 00 00
00 48 89 45 d0 31 c0 e8 c0 a5 03 00 4c 89 f8 48 c1 e8 03 <42> 0f b6 04 28
84 c0 74 08 3c 03 0f 8e 9f 02 00 00 4c 8b ad 68 ff
RSP: 0018:ffff88809a567a30 EFLAGS: 00010246
RAX: 0000000000000000 RBX: ffff88809a567aa8 RCX: ffffffff825b97b5
RDX: 0000000000000000 RSI: ffffffff816edf30 RDI: 0000000000000000
RBP: ffff88809a567ad0 R08: ffff88808e4d2600 R09: ffffed1014af1713
R10: ffffed1014af1712 R11: 0000000000000003 R12: 0000000000000001
R13: dffffc0000000000 R14: 0000000000000000 R15: 0000000000000000
FS: 0000555555618880(0000) GS:ffff8880ae800000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000020000084 CR3: 000000008b2ec000 CR4: 00000000001406f0


---
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For information about bisection process see: https://goo.gl/tpsmEJ#bisection
syzbot can test patches for this bug, for details see:
https://goo.gl/tpsmEJ#testing-patches

[Eric Biggers]

From: Eric Biggers <ebig...@google.com>

fs_context::user_ns is used by fuse_parse_param(), even during remount,
so it needs to be set to the existing value for reconfigure.

Reproducer:

#include <fcntl.h>
#include <sys/mount.h>

int main()
{
char opts[128];
int fd = open("/dev/fuse", O_RDWR);

sprintf(opts, "fd=%d,rootmode=040000,user_id=0,group_id=0", fd);
mkdir("mnt", 0777);
mount("foo", "mnt", "fuse.foo", 0, opts);
mount("foo", "mnt", "fuse.foo", MS_REMOUNT, opts);
}

Crash:
BUG: kernel NULL pointer dereference, address: 0000000000000000
#PF: supervisor read access in kernel mode
#PF: error_code(0x0000) - not-present page
PGD 0 P4D 0
Oops: 0000 [#1] SMP
CPU: 0 PID: 129 Comm: syz_make_kuid Not tainted 5.3.0-rc5-next-20190821 #3
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.12.0-20181126_142135-anatol 04/01/2014
RIP: 0010:map_id_range_down+0xb/0xc0 kernel/user_namespace.c:291
[...]
Call Trace:
map_id_down kernel/user_namespace.c:312 [inline]
make_kuid+0xe/0x10 kernel/user_namespace.c:389
fuse_parse_param+0x116/0x210 fs/fuse/inode.c:523
vfs_parse_fs_param+0xdb/0x1b0 fs/fs_context.c:145
vfs_parse_fs_string+0x6a/0xa0 fs/fs_context.c:188
generic_parse_monolithic+0x85/0xc0 fs/fs_context.c:228
parse_monolithic_mount_data+0x1b/0x20 fs/fs_context.c:708
do_remount fs/namespace.c:2525 [inline]
do_mount+0x39a/0xa60 fs/namespace.c:3107
ksys_mount+0x7d/0xd0 fs/namespace.c:3325
__do_sys_mount fs/namespace.c:3339 [inline]
__se_sys_mount fs/namespace.c:3336 [inline]
__x64_sys_mount+0x20/0x30 fs/namespace.c:3336
do_syscall_64+0x4a/0x1a0 arch/x86/entry/common.c:290
entry_SYSCALL_64_after_hwframe+0x49/0xbe

Reported-by: syzbot+7d6a57...@syzkaller.appspotmail.com
Fixes: 408cbe695350 ("vfs: Convert fuse to use the new mount API")
Cc: David Howells <dhow...@redhat.com>
Cc: Miklos Szeredi <mik...@szeredi.hu>
Signed-off-by: Eric Biggers <ebig...@google.com>
---
fs/fs_context.c | 4 +---
1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/fs/fs_context.c b/fs/fs_context.c
index cc61d305dc4b..44c4174b250a 100644
--- a/fs/fs_context.c
+++ b/fs/fs_context.c
@@ -279,10 +279,8 @@ static struct fs_context *alloc_fs_context(struct file_system_type *fs_type,
fc->user_ns = get_user_ns(reference->d_sb->s_user_ns);
break;
case FS_CONTEXT_FOR_RECONFIGURE:
- /* We don't pin any namespaces as the superblock's
- * subscriptions cannot be changed at this point.
- */
atomic_inc(&reference->d_sb->s_active);
+ fc->user_ns = get_user_ns(reference->d_sb->s_user_ns);
fc->root = dget(reference);
break;
}
--
2.22.1

[Eric Biggers]

Ping.

[Eric Biggers]

Ping. This is still broken in linux-next.

- Eric