Hello,
syzbot found the following crash on:
HEAD commit: 7ae77150 Merge tag 'powerpc-5.8-1' of git://git.kernel.org..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=16e12212100000
kernel config: https://syzkaller.appspot.com/x/.config?x=d195fe572fb15312
dashboard link: https://syzkaller.appspot.com/bug?extid=4abac52934a48af5ff19
compiler: gcc (GCC) 9.0.0 20181231 (experimental)
Unfortunately, I don't have any reproducer for this crash yet.
IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: [email protected]
RBP: 000000000078bf00 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000005
R13: 0000000000000751 R14: 00000000004ca3ea R15: 00007f8970ff76d4
general protection fault, probably for non-canonical address 0xdffffc0000000001: 0000 [#1] PREEMPT SMP KASAN
KASAN: null-ptr-deref in range [0x0000000000000008-0x000000000000000f]
CPU: 0 PID: 6840 Comm: syz-executor.2 Not tainted 5.7.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
RIP: 0010:proc_kill_sb+0x4d/0x110 fs/proc/root.c:267
Code: c1 ea 03 80 3c 02 00 0f 85 ad 00 00 00 49 8b ac 24 68 06 00 00 48 b8 00 00 00 00 00 fc ff df 48 8d 7d 08 48 89 fa 48 c1 ea 03 <80> 3c 02 00 0f 85 a1 00 00 00 4c 8b 6d 08 4d 85 ed 74 0d e8 cb 51
RSP: 0018:ffffc90007b67d48 EFLAGS: 00010202
RAX: dffffc0000000000 RBX: 0000000000000001 RCX: ffffc9000d6d1000
RDX: 0000000000000001 RSI: ffffffff81e37c9d RDI: 0000000000000008
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000001
R10: ffffffff8c347a2f R11: fffffbfff1868f45 R12: ffff888059e1a000
R13: 00000000fffffff4 R14: 0000000000000000 R15: ffff888059e1a068
FS: 00007f8970ff7700(0000) GS:ffff8880ae600000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000000000073c138 CR3: 00000000588dc000 CR4: 00000000001406f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
deactivate_locked_super+0x8c/0xf0 fs/super.c:335
vfs_get_super+0x258/0x2d0 fs/super.c:1212
vfs_get_tree+0x89/0x2f0 fs/super.c:1547
do_new_mount fs/namespace.c:2874 [inline]
do_mount+0x1306/0x1b40 fs/namespace.c:3199
__do_sys_mount fs/namespace.c:3409 [inline]
__se_sys_mount fs/namespace.c:3386 [inline]
__x64_sys_mount+0x18f/0x230 fs/namespace.c:3386
do_syscall_64+0xf6/0x7d0 arch/x86/entry/common.c:295
entry_SYSCALL_64_after_hwframe+0x49/0xb3
RIP: 0033:0x45ca69
Code: 0d b7 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 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 0f 83 db b6 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f8970ff6c78 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 00000000004f62c0 RCX: 000000000045ca69
RDX: 00000000200000c0 RSI: 0000000020000200 RDI: 0000000020000340
RBP: 000000000078bf00 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000005
R13: 0000000000000751 R14: 00000000004ca3ea R15: 00007f8970ff76d4
Modules linked in:
---[ end trace 7f26d357bd21d77e ]---
RIP: 0010:proc_kill_sb+0x4d/0x110 fs/proc/root.c:267
Code: c1 ea 03 80 3c 02 00 0f 85 ad 00 00 00 49 8b ac 24 68 06 00 00 48 b8 00 00 00 00 00 fc ff df 48 8d 7d 08 48 89 fa 48 c1 ea 03 <80> 3c 02 00 0f 85 a1 00 00 00 4c 8b 6d 08 4d 85 ed 74 0d e8 cb 51
RSP: 0018:ffffc90007b67d48 EFLAGS: 00010202
RAX: dffffc0000000000 RBX: 0000000000000001 RCX: ffffc9000d6d1000
RDX: 0000000000000001 RSI: ffffffff81e37c9d RDI: 0000000000000008
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000001
R10: ffffffff8c347a2f R11: fffffbfff1868f45 R12: ffff888059e1a000
R13: 00000000fffffff4 R14: 0000000000000000 R15: ffff888059e1a068
FS: 00007f8970ff7700(0000) GS:ffff8880ae600000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f19326ab000 CR3: 00000000588dc000 CR4: 00000000001406f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
---
This bug is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at [email protected].
syzbot will keep track of this bug report. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
syzbot found that proc_fill_super() fails before filling up sb->s_fs_info,
deactivate_locked_super() will be called and sb->s_fs_info will be NULL.
The proc_kill_sb() does not expect fs_info to be NULL which is wrong.
Link: https://lore.kernel.org/lkml/[email protected]
Reported-by: [email protected]
Fixes: fa10fed30f25 ("proc: allow to mount many instances of proc in one pid namespace")
Signed-off-by: Alexey Gladkov <[email protected]>
---
fs/proc/root.c | 15 +++++++++------
1 file changed, 9 insertions(+), 6 deletions(-)
diff --git a/fs/proc/root.c b/fs/proc/root.c
index ffebed1999e5..a715eb9f196a 100644
--- a/fs/proc/root.c
+++ b/fs/proc/root.c
@@ -264,15 +264,18 @@ static void proc_kill_sb(struct super_block *sb)
{
struct proc_fs_info *fs_info = proc_sb_info(sb);
- if (fs_info->proc_self)
- dput(fs_info->proc_self);
+ if (fs_info) {
+ if (fs_info->proc_self)
+ dput(fs_info->proc_self);
- if (fs_info->proc_thread_self)
- dput(fs_info->proc_thread_self);
+ if (fs_info->proc_thread_self)
+ dput(fs_info->proc_thread_self);
+
+ put_pid_ns(fs_info->pid_ns);
+ kfree(fs_info);
+ }
kill_anon_super(sb);
- put_pid_ns(fs_info->pid_ns);
- kfree(fs_info);
}
static struct file_system_type proc_fs_type = {
--
2.25.4
Alexey Gladkov <[email protected]> writes:
> syzbot found that proc_fill_super() fails before filling up sb->s_fs_info,
> deactivate_locked_super() will be called and sb->s_fs_info will be NULL.
> The proc_kill_sb() does not expect fs_info to be NULL which is wrong.
For the case where s_fs_info is never allocated this looks correct.
That is because generic_shutdown_super has a special for !sb->s_root.
However for the existing cases I can't convince myself that it is safe
to change the order we free the pid namespace and free fs_info.
There is a lot of code that can run while generic_shutdown_super is
running and purging all of the inodes. We have crazy things like
proc_flush_pid that might care, as well proc_evict_inode.
I haven't found anything that actually references fs_info or actually
depends on the pid namespace living longer than the proc inode but it
would be really easy to miss something.
Can you send a v2 version does not change the order things are freed in
for the case where we do allocate fs_info. That will make it trivially
safe to apply.
Otherwise this looks like a very good patch.
Thank you,
Eric
> Link: https://lore.kernel.org/lkml/[email protected]
> Reported-by: [email protected]
> Fixes: fa10fed30f25 ("proc: allow to mount many instances of proc in one pid namespace")
> Signed-off-by: Alexey Gladkov <[email protected]>
> ---
> fs/proc/root.c | 15 +++++++++------
> 1 file changed, 9 insertions(+), 6 deletions(-)
>
> diff --git a/fs/proc/root.c b/fs/proc/root.c
> index ffebed1999e5..a715eb9f196a 100644
> --- a/fs/proc/root.c
> +++ b/fs/proc/root.c
> @@ -264,15 +264,18 @@ static void proc_kill_sb(struct super_block *sb)
> {
> struct proc_fs_info *fs_info = proc_sb_info(sb);
>
> - if (fs_info->proc_self)
> - dput(fs_info->proc_self);
> + if (fs_info) {
> + if (fs_info->proc_self)
> + dput(fs_info->proc_self);
>
> - if (fs_info->proc_thread_self)
> - dput(fs_info->proc_thread_self);
> + if (fs_info->proc_thread_self)
> + dput(fs_info->proc_thread_self);
> +
> + put_pid_ns(fs_info->pid_ns);
> + kfree(fs_info);
> + }
>
> kill_anon_super(sb);
> - put_pid_ns(fs_info->pid_ns);
> - kfree(fs_info);
> }
>
> static struct file_system_type proc_fs_type = {
syzbot found that proc_fill_super() fails before filling up sb->s_fs_info,
deactivate_locked_super() will be called and sb->s_fs_info will be NULL.
The proc_kill_sb() does not expect fs_info to be NULL which is wrong.
Link: https://lore.kernel.org/lkml/[email protected]
Reported-by: [email protected]
Fixes: fa10fed30f25 ("proc: allow to mount many instances of proc in one pid namespace")
Signed-off-by: Alexey Gladkov <[email protected]>
---
fs/proc/root.c | 10 ++++++----
1 file changed, 6 insertions(+), 4 deletions(-)
diff --git a/fs/proc/root.c b/fs/proc/root.c
index ffebed1999e5..5e444d4f9717 100644
--- a/fs/proc/root.c
+++ b/fs/proc/root.c
@@ -264,11 +264,13 @@ static void proc_kill_sb(struct super_block *sb)
{
struct proc_fs_info *fs_info = proc_sb_info(sb);
- if (fs_info->proc_self)
- dput(fs_info->proc_self);
+ if (!fs_info) {
+ kill_anon_super(sb);
+ return;
+ }
- if (fs_info->proc_thread_self)
- dput(fs_info->proc_thread_self);
+ dput(fs_info->proc_self);
+ dput(fs_info->proc_thread_self);
kill_anon_super(sb);
put_pid_ns(fs_info->pid_ns);
--
2.25.4
Alexey Gladkov <[email protected]> writes:
> syzbot found that proc_fill_super() fails before filling up sb->s_fs_info,
> deactivate_locked_super() will be called and sb->s_fs_info will be NULL.
> The proc_kill_sb() does not expect fs_info to be NULL which is wrong.
>
> Link: https://lore.kernel.org/lkml/[email protected]
> Reported-by: [email protected]
> Fixes: fa10fed30f25 ("proc: allow to mount many instances of proc in one pid namespace")
> Signed-off-by: Alexey Gladkov <[email protected]>
applied
Eric
On Wed, Jun 10, 2020 at 12:12:54PM -0500, Eric W. Biederman wrote:
> > {
> > struct proc_fs_info *fs_info = proc_sb_info(sb);
> >
> > - if (fs_info->proc_self)
> > - dput(fs_info->proc_self);
> > + if (fs_info) {
> > + if (fs_info->proc_self)
> > + dput(fs_info->proc_self);
> >
> > - if (fs_info->proc_thread_self)
> > - dput(fs_info->proc_thread_self);
> > + if (fs_info->proc_thread_self)
> > + dput(fs_info->proc_thread_self);
> > +
> > + put_pid_ns(fs_info->pid_ns);
> > + kfree(fs_info);
While we are at it, dput(NULL) is an explicit no-op.