[PATCH v3] proc: proc_pid_ns takes super_block as an argument

From: Alexey Gladkov
Date: Mon May 18 2020 - 11:09:52 EST

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syzbot writes:
> general protection fault, probably for non-canonical address 0xdffffc0000000005: 0000 [#1] PREEMPT SMP KASAN
> KASAN: null-ptr-deref in range [0x0000000000000028-0x000000000000002f]
> CPU: 0 PID: 6698 Comm: sshd Not tainted 5.7.0-rc5-next-20200515-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> RIP: 0010:tomoyo_get_local_path+0x450/0x800 security/tomoyo/realpath.c:165
> Code: 48 89 fa 48 c1 ea 03 80 3c 02 00 0f 85 b4 03 00 00 48 b8 00 00 00 00 00 fc ff df 4d 8b 7f 60 49 8d 7f 28 48 89 fa 48 c1 ea 03 <80> 3c 02 00 0f 85 87 03 00 00 48 b8 00 00 00 00 00 fc ff df 4d 8b
> RSP: 0018:ffffc900063d7450 EFLAGS: 00010206
> RAX: dffffc0000000000 RBX: ffff88809975c000 RCX: ffffffff8363deda
> RDX: 0000000000000005 RSI: ffffffff8363dee8 RDI: 0000000000000028
> RBP: 1ffff92000c7ae8b R08: ffff8880a47644c0 R09: fffffbfff155a0a2
> R10: ffffffff8aad050f R11: fffffbfff155a0a1 R12: ffff88809df3cfea
> R13: ffff88809df3c000 R14: 0000000000001a2a R15: 0000000000000000
> FS: 00007efe13ce28c0(0000) GS:ffff8880ae600000(0000) knlGS:0000000000000000
> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 000055e78cf578f5 CR3: 00000000987ed000 CR4: 00000000001406f0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
> tomoyo_realpath_from_path+0x393/0x620 security/tomoyo/realpath.c:282
> tomoyo_get_realpath security/tomoyo/file.c:151 [inline]
> tomoyo_path_number_perm+0x1c2/0x4d0 security/tomoyo/file.c:723
> tomoyo_path_mknod+0x10d/0x190 security/tomoyo/tomoyo.c:246
> security_path_mknod+0x116/0x180 security/security.c:1072
> may_o_create fs/namei.c:2905 [inline]
> lookup_open+0x5ae/0x1320 fs/namei.c:3046
> open_last_lookups fs/namei.c:3155 [inline]
> path_openat+0x93c/0x27f0 fs/namei.c:3343
> do_filp_open+0x192/0x260 fs/namei.c:3373
> do_sys_openat2+0x585/0x7d0 fs/open.c:1179
> do_sys_open+0xc3/0x140 fs/open.c:1195
> do_syscall_64+0xf6/0x7d0 arch/x86/entry/common.c:295
> entry_SYSCALL_64_after_hwframe+0x49/0xb3
> RIP: 0033:0x7efe11e4b6f0
> Code: 00 f7 d8 64 89 01 48 83 c8 ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 83 3d 19 30 2c 00 00 75 10 b8 02 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 31 c3 48 83 ec 08 e8 fe 9d 01 00 48 89 04 24
> RSP: 002b:00007ffc3d0894d8 EFLAGS: 00000246 ORIG_RAX: 0000000000000002
> RAX: ffffffffffffffda RBX: 000055e78f0bc110 RCX: 00007efe11e4b6f0
> RDX: 00000000000001b6 RSI: 0000000000000241 RDI: 000055e78cf578f5
> RBP: 0000000000000004 R08: 0000000000000004 R09: 0000000000000001
> R10: 0000000000000240 R11: 0000000000000246 R12: 000055e78cf2851e
> R13: 0000000000000001 R14: 0000000000000000 R15: 0000000000000000
> Modules linked in:
> ---[ end trace 0a58064de06d50f4 ]---
> RIP: 0010:tomoyo_get_local_path+0x450/0x800 security/tomoyo/realpath.c:165
> Code: 48 89 fa 48 c1 ea 03 80 3c 02 00 0f 85 b4 03 00 00 48 b8 00 00 00 00 00 fc ff df 4d 8b 7f 60 49 8d 7f 28 48 89 fa 48 c1 ea 03 <80> 3c 02 00 0f 85 87 03 00 00 48 b8 00 00 00 00 00 fc ff df 4d 8b
> RSP: 0018:ffffc900063d7450 EFLAGS: 00010206
> RAX: dffffc0000000000 RBX: ffff88809975c000 RCX: ffffffff8363deda
> RDX: 0000000000000005 RSI: ffffffff8363dee8 RDI: 0000000000000028
> RBP: 1ffff92000c7ae8b R08: ffff8880a47644c0 R09: fffffbfff155a0a2
> R10: ffffffff8aad050f R11: fffffbfff155a0a1 R12: ffff88809df3cfea
> R13: ffff88809df3c000 R14: 0000000000001a2a R15: 0000000000000000
> FS: 00007efe13ce28c0(0000) GS:ffff8880ae600000(0000) knlGS:0000000000000000
> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 000055dfe16c15f8 CR3: 00000000987ed000 CR4: 00000000001406f0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400

This is happening as part of creating a file or a device node. The
dentry that is passed in most likely comes from d_alloc_parallel and
does not have a d_inode.

Before c59f415a7cb6, Tomoyo received pid_ns from proc's s_fs_info
directly. Since proc_pid_ns() can only work with inode, using it in
the tomoyo_get_local_path() was wrong.

To avoid creating more functions for getting proc_ns would be more
correct to change the argument type of the proc_pid_ns() function.

In this case, Tomoyo can use the existing super_block to get pid_ns.

Reported-by: syzbot+c1af344512918c61362c@xxxxxxxxxxxxxxxxxxxxxxxxx
Fixes: c59f415a7cb6 ("Use proc_pid_ns() to get pid_namespace from the proc superblock")
Signed-off-by: Alexey Gladkov <gladkov.alexey@xxxxxxxxx>
---
fs/locks.c | 4 ++--
fs/proc/array.c | 2 +-
fs/proc/base.c | 10 +++++-----
fs/proc/self.c | 2 +-
fs/proc/thread_self.c | 2 +-
include/linux/proc_fs.h | 4 ++--
kernel/fork.c | 2 +-
net/ipv6/ip6_flowlabel.c | 2 +-
security/tomoyo/realpath.c | 2 +-
9 files changed, 15 insertions(+), 15 deletions(-)

diff --git a/fs/locks.c b/fs/locks.c
index 399c5dbb72c4..ab702d6efb55 100644
--- a/fs/locks.c
+++ b/fs/locks.c
@@ -2823,7 +2823,7 @@ static void lock_get_status(struct seq_file *f, struct file_lock *fl,
{
struct inode *inode = NULL;
unsigned int fl_pid;
- struct pid_namespace *proc_pidns = proc_pid_ns(file_inode(f->file));
+ struct pid_namespace *proc_pidns = proc_pid_ns(file_inode(f->file)->i_sb);

fl_pid = locks_translate_pid(fl, proc_pidns);
/*
@@ -2901,7 +2901,7 @@ static int locks_show(struct seq_file *f, void *v)
{
struct locks_iterator *iter = f->private;
struct file_lock *fl, *bfl;
- struct pid_namespace *proc_pidns = proc_pid_ns(file_inode(f->file));
+ struct pid_namespace *proc_pidns = proc_pid_ns(file_inode(f->file)->i_sb);

fl = hlist_entry(v, struct file_lock, fl_link);

diff --git a/fs/proc/array.c b/fs/proc/array.c
index 8e16f14bb05a..043311014db2 100644
--- a/fs/proc/array.c
+++ b/fs/proc/array.c
@@ -728,7 +728,7 @@ static int children_seq_show(struct seq_file *seq, void *v)
{
struct inode *inode = file_inode(seq->file);

- seq_printf(seq, "%d ", pid_nr_ns(v, proc_pid_ns(inode)));
+ seq_printf(seq, "%d ", pid_nr_ns(v, proc_pid_ns(inode->i_sb)));
return 0;
}

diff --git a/fs/proc/base.c b/fs/proc/base.c
index 5a307b3bb2d1..30c9fceca0b7 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -754,7 +754,7 @@ static const struct inode_operations proc_def_inode_operations = {
static int proc_single_show(struct seq_file *m, void *v)
{
struct inode *inode = m->private;
- struct pid_namespace *ns = proc_pid_ns(inode);
+ struct pid_namespace *ns = proc_pid_ns(inode->i_sb);
struct pid *pid = proc_pid(inode);
struct task_struct *task;
int ret;
@@ -1423,7 +1423,7 @@ static const struct file_operations proc_fail_nth_operations = {
static int sched_show(struct seq_file *m, void *v)
{
struct inode *inode = m->private;
- struct pid_namespace *ns = proc_pid_ns(inode);
+ struct pid_namespace *ns = proc_pid_ns(inode->i_sb);
struct task_struct *p;

p = get_proc_task(inode);
@@ -2466,7 +2466,7 @@ static int proc_timers_open(struct inode *inode, struct file *file)
return -ENOMEM;

tp->pid = proc_pid(inode);
- tp->ns = proc_pid_ns(inode);
+ tp->ns = proc_pid_ns(inode->i_sb);
return 0;
}

@@ -3377,7 +3377,7 @@ int proc_pid_readdir(struct file *file, struct dir_context *ctx)
{
struct tgid_iter iter;
struct proc_fs_info *fs_info = proc_sb_info(file_inode(file)->i_sb);
- struct pid_namespace *ns = proc_pid_ns(file_inode(file));
+ struct pid_namespace *ns = proc_pid_ns(file_inode(file)->i_sb);
loff_t pos = ctx->pos;

if (pos >= PID_MAX_LIMIT + TGID_OFFSET)
@@ -3730,7 +3730,7 @@ static int proc_task_readdir(struct file *file, struct dir_context *ctx)
/* f_version caches the tgid value that the last readdir call couldn't
* return. lseek aka telldir automagically resets f_version to 0.
*/
- ns = proc_pid_ns(inode);
+ ns = proc_pid_ns(inode->i_sb);
tid = (int)file->f_version;
file->f_version = 0;
for (task = first_tid(proc_pid(inode), tid, ctx->pos - 2, ns);
diff --git a/fs/proc/self.c b/fs/proc/self.c
index 309301ac0136..ca5158fa561c 100644
--- a/fs/proc/self.c
+++ b/fs/proc/self.c
@@ -12,7 +12,7 @@ static const char *proc_self_get_link(struct dentry *dentry,
struct inode *inode,
struct delayed_call *done)
{
- struct pid_namespace *ns = proc_pid_ns(inode);
+ struct pid_namespace *ns = proc_pid_ns(inode->i_sb);
pid_t tgid = task_tgid_nr_ns(current, ns);
char *name;

diff --git a/fs/proc/thread_self.c b/fs/proc/thread_self.c
index 2493cbbdfa6f..ac284f409568 100644
--- a/fs/proc/thread_self.c
+++ b/fs/proc/thread_self.c
@@ -12,7 +12,7 @@ static const char *proc_thread_self_get_link(struct dentry *dentry,
struct inode *inode,
struct delayed_call *done)
{
- struct pid_namespace *ns = proc_pid_ns(inode);
+ struct pid_namespace *ns = proc_pid_ns(inode->i_sb);
pid_t tgid = task_tgid_nr_ns(current, ns);
pid_t pid = task_pid_nr_ns(current, ns);
char *name;
diff --git a/include/linux/proc_fs.h b/include/linux/proc_fs.h
index 2cb424e6f36a..6ec524d8842c 100644
--- a/include/linux/proc_fs.h
+++ b/include/linux/proc_fs.h
@@ -202,9 +202,9 @@ int open_related_ns(struct ns_common *ns,
struct ns_common *(*get_ns)(struct ns_common *ns));

/* get the associated pid namespace for a file in procfs */
-static inline struct pid_namespace *proc_pid_ns(const struct inode *inode)
+static inline struct pid_namespace *proc_pid_ns(struct super_block *sb)
{
- return proc_sb_info(inode->i_sb)->pid_ns;
+ return proc_sb_info(sb)->pid_ns;
}

#endif /* _LINUX_PROC_FS_H */
diff --git a/kernel/fork.c b/kernel/fork.c
index 4385f3d639f2..e7bdaccad942 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1745,7 +1745,7 @@ static void pidfd_show_fdinfo(struct seq_file *m, struct file *f)
pid_t nr = -1;

if (likely(pid_has_task(pid, PIDTYPE_PID))) {
- ns = proc_pid_ns(file_inode(m->file));
+ ns = proc_pid_ns(file_inode(m->file)->i_sb);
nr = pid_nr_ns(pid, ns);
}

diff --git a/net/ipv6/ip6_flowlabel.c b/net/ipv6/ip6_flowlabel.c
index d64b83e85642..ce4fbba4acce 100644
--- a/net/ipv6/ip6_flowlabel.c
+++ b/net/ipv6/ip6_flowlabel.c
@@ -779,7 +779,7 @@ static void *ip6fl_seq_start(struct seq_file *seq, loff_t *pos)
{
struct ip6fl_iter_state *state = ip6fl_seq_private(seq);

- state->pid_ns = proc_pid_ns(file_inode(seq->file));
+ state->pid_ns = proc_pid_ns(file_inode(seq->file)->i_sb);

rcu_read_lock_bh();
return *pos ? ip6fl_get_idx(seq, *pos - 1) : SEQ_START_TOKEN;
diff --git a/security/tomoyo/realpath.c b/security/tomoyo/realpath.c
index 08b096e2f7e3..df4798980416 100644
--- a/security/tomoyo/realpath.c
+++ b/security/tomoyo/realpath.c
@@ -162,7 +162,7 @@ static char *tomoyo_get_local_path(struct dentry *dentry, char * const buffer,
if (sb->s_magic == PROC_SUPER_MAGIC && *pos == '/') {
char *ep;
const pid_t pid = (pid_t) simple_strtoul(pos + 1, &ep, 10);
- struct pid_namespace *proc_pidns = proc_pid_ns(d_inode(dentry));
+ struct pid_namespace *proc_pidns = proc_pid_ns(sb);

if (*ep == '/' && pid && pid ==
task_tgid_nr_ns(current, proc_pidns)) {
--
2.25.4

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