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Message-ID: <c5a2cf05-8e30-1fac-3c48-d4b508ea9009@redhat.com>
Date: Mon, 7 Nov 2022 20:03:10 +0800
From: Xiubo Li <xiubli@...hat.com>
To: Jeff Layton <jlayton@...nel.org>, viro@...iv.linux.org.uk,
chuck.lever@...cle.com
Cc: axboe@...nel.dk, asml.silence@...il.com,
linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
io-uring@...r.kernel.org, ceph-devel@...r.kernel.org,
mchangir@...hat.com, idryomov@...il.com, lhenriques@...e.de,
gfarnum@...hat.com
Subject: Re: [RFC PATCH] fs/lock: increase the filp's reference for
Posix-style locks
On 07/11/2022 18:33, Jeff Layton wrote:
> On Mon, 2022-11-07 at 17:52 +0800, xiubli@...hat.com wrote:
>> From: Xiubo Li <xiubli@...hat.com>
>>
>> When closing the file descripters in parallel in multiple threads,
>> who are sharing the same file descripters, the filp_close() will
>> remove all the Posix-style locks. But if two threads both calling
>> the filp_close() it may race and cause use-after-free crash:
>>
>> PID: 327771 TASK: ffff952aa1db3180 CPU: 8 COMMAND: "db2fmp"
>> #0 [ffff95202f33b960] machine_kexec at ffffffff890662f4
>> #1 [ffff95202f33b9c0] __crash_kexec at ffffffff89122b82
>> #2 [ffff95202f33ba90] crash_kexec at ffffffff89122c70
>> #3 [ffff95202f33baa8] oops_end at ffffffff89791798
>> #4 [ffff95202f33bad0] no_context at ffffffff89075d14
>> #5 [ffff95202f33bb20] __bad_area_nosemaphore at ffffffff89075fe2
>> #6 [ffff95202f33bb70] bad_area_nosemaphore at ffffffff89076104
>> #7 [ffff95202f33bb80] __do_page_fault at ffffffff89794750
>> #8 [ffff95202f33bbf0] do_page_fault at ffffffff89794975
>> #9 [ffff95202f33bc20] page_fault at ffffffff89790778
>> [exception RIP: ceph_fl_release_lock+20]
>> RIP: ffffffffc08247a4 RSP: ffff95202f33bcd0 RFLAGS: 00010286
>> RAX: ffff952d4ebd8a00 RBX: 0000000000000000 RCX: dead000000000200
>> RDX: ffff95202f33bd60 RSI: ffff95202f33bd60 RDI: ffff9526b6ac5b00
>> RBP: ffff95202f33bce0 R8: ffff9526b6ac5b18 R9: ffffffffc083c368
>> R10: 0000000000001109 R11: 0000000000000000 R12: ffff95202f33bd60
>> R13: ffff9526b6ac5b00 R14: 0000000000000000 R15: 0000000000000000
>> ORIG_RAX: ffffffffffffffff CS: 0010 SS: 0018
>> #10 [ffff95202f33bce8] locks_release_private at ffffffff892ab3d7
>> #11 [ffff95202f33bd00] locks_free_lock at ffffffff892ac34d
>> #12 [ffff95202f33bd18] locks_dispose_list at ffffffff892ac44b
>> #13 [ffff95202f33bd40] __posix_lock_file at ffffffff892acdfa
>> #14 [ffff95202f33bda8] posix_lock_file at ffffffff892ad146
>> #15 [ffff95202f33bdb8] ceph_lock at ffffffffc0824e8a [ceph]
>> #16 [ffff95202f33bdf8] vfs_lock_file at ffffffff892ad185
>> #17 [ffff95202f33be08] locks_remove_posix at ffffffff892ad239
>> #18 [ffff95202f33bee0] locks_remove_posix at ffffffff892ad2a0
>> #19 [ffff95202f33bef0] filp_close at ffffffff8924baa6
>> #20 [ffff95202f33bf18] __close_fd at ffffffff8926f89c
>> #21 [ffff95202f33bf40] sys_close at ffffffff8924d503
>> #22 [ffff95202f33bf50] system_call_fastpath at ffffffff89799f92
>> RIP: 00007f806ec446ab RSP: 00007f80517f0d90 RFLAGS: 00010206
>> RAX: 0000000000000003 RBX: 00007f8030001a20 RCX: 00007f80300386b0
>> RDX: 00007f806ef0d880 RSI: 0000000000000001 RDI: 0000000000000006
>> RBP: 00007f806ef0e3c0 R8: 00007f80517fa700 R9: 0000000000000000
>> R10: 0000000000000000 R11: 0000000000000206 R12: 0000000000000000
>> R13: 00007f80300035b0 R14: 00007f80517f1104 R15: 000000000000006c
>> ORIG_RAX: 0000000000000003 CS: 0033 SS: 002b
>>
>> We need to make sure that the filp in the file_lock shouldn't be
>> release when any file_lock is still referring to it.
>>
>> For the Posix-style locks, whose owner will be the thread ids, we
>> will increase the filp's reference.
>>
>> URL: https://tracker.ceph.com/issues/57986
>> Signed-off-by: Xiubo Li <xiubli@...hat.com>
>> ---
>> drivers/android/binder.c | 2 +-
>> fs/file.c | 15 ++++++++++-----
>> fs/locks.c | 18 +++++++++++++++---
>> include/linux/fs.h | 14 ++++++++++++++
>> io_uring/openclose.c | 3 ++-
>> 5 files changed, 42 insertions(+), 10 deletions(-)
>>
>> diff --git a/drivers/android/binder.c b/drivers/android/binder.c
>> index 880224ec6abb..03692564d940 100644
>> --- a/drivers/android/binder.c
>> +++ b/drivers/android/binder.c
>> @@ -1924,7 +1924,7 @@ static void binder_deferred_fd_close(int fd)
>> if (twcb->file) {
>> // pin it until binder_do_fd_close(); see comments there
>> get_file(twcb->file);
>> - filp_close(twcb->file, current->files);
>> + filp_close(twcb->file, file_lock_make_thread_owner(current->files));
>> task_work_add(current, &twcb->twork, TWA_RESUME);
>> } else {
>> kfree(twcb);
>> diff --git a/fs/file.c b/fs/file.c
>> index 5f9c802a5d8d..39ad8e74a8d9 100644
>> --- a/fs/file.c
>> +++ b/fs/file.c
>> @@ -417,6 +417,7 @@ static struct fdtable *close_files(struct files_struct * files)
>> * files structure.
>> */
>> struct fdtable *fdt = rcu_dereference_raw(files->fdt);
>> + fl_owner_t owner = file_lock_make_thread_owner(files);
>> unsigned int i, j = 0;
>>
>> for (;;) {
>> @@ -429,7 +430,7 @@ static struct fdtable *close_files(struct files_struct * files)
>> if (set & 1) {
>> struct file * file = xchg(&fdt->fd[i], NULL);
>> if (file) {
>> - filp_close(file, files);
>> + filp_close(file, owner);
>> cond_resched();
>> }
>> }
>> @@ -653,6 +654,7 @@ static struct file *pick_file(struct files_struct *files, unsigned fd)
>> int close_fd(unsigned fd)
>> {
>> struct files_struct *files = current->files;
>> + fl_owner_t owner = file_lock_make_thread_owner(files);
>> struct file *file;
>>
>> spin_lock(&files->file_lock);
>> @@ -661,7 +663,7 @@ int close_fd(unsigned fd)
>> if (!file)
>> return -EBADF;
>>
>> - return filp_close(file, files);
>> + return filp_close(file, owner);
>> }
>> EXPORT_SYMBOL(close_fd); /* for ksys_close() */
>>
>> @@ -695,6 +697,7 @@ static inline void __range_cloexec(struct files_struct *cur_fds,
>> static inline void __range_close(struct files_struct *cur_fds, unsigned int fd,
>> unsigned int max_fd)
>> {
>> + fl_owner_t owner = file_lock_make_thread_owner(cur_fds);
>> unsigned n;
>>
>> rcu_read_lock();
>> @@ -711,7 +714,7 @@ static inline void __range_close(struct files_struct *cur_fds, unsigned int fd,
>>
>> if (file) {
>> /* found a valid file to close */
>> - filp_close(file, cur_fds);
>> + filp_close(file, owner);
>> cond_resched();
>> }
>> }
>> @@ -816,6 +819,7 @@ struct file *close_fd_get_file(unsigned int fd)
>>
>> void do_close_on_exec(struct files_struct *files)
>> {
>> + fl_owner_t owner = file_lock_make_thread_owner(files);
>> unsigned i;
>> struct fdtable *fdt;
>>
>> @@ -841,7 +845,7 @@ void do_close_on_exec(struct files_struct *files)
>> rcu_assign_pointer(fdt->fd[fd], NULL);
>> __put_unused_fd(files, fd);
>> spin_unlock(&files->file_lock);
>> - filp_close(file, files);
>> + filp_close(file, owner);
>> cond_resched();
>> spin_lock(&files->file_lock);
>> }
>> @@ -1080,6 +1084,7 @@ static int do_dup2(struct files_struct *files,
>> struct file *file, unsigned fd, unsigned flags)
>> __releases(&files->file_lock)
>> {
>> + fl_owner_t owner = file_lock_make_thread_owner(files);
>> struct file *tofree;
>> struct fdtable *fdt;
>>
>> @@ -1111,7 +1116,7 @@ __releases(&files->file_lock)
>> spin_unlock(&files->file_lock);
>>
>> if (tofree)
>> - filp_close(tofree, files);
>> + filp_close(tofree, owner);
>>
>> return fd;
>>
>> diff --git a/fs/locks.c b/fs/locks.c
>> index 607f94a0e789..e8b67f87e0ee 100644
>> --- a/fs/locks.c
>> +++ b/fs/locks.c
>> @@ -331,6 +331,8 @@ EXPORT_SYMBOL_GPL(locks_owner_has_blockers);
>> /* Free a lock which is not in use. */
>> void locks_free_lock(struct file_lock *fl)
>> {
>> + if (fl->fl_file && file_lock_is_thread_owner(fl->fl_owner))
>> + fput(fl->fl_file);
>> locks_release_private(fl);
>> kmem_cache_free(filelock_cache, fl);
>> }
>> @@ -384,7 +386,10 @@ void locks_copy_lock(struct file_lock *new, struct file_lock *fl)
>>
>> locks_copy_conflock(new, fl);
>>
>> - new->fl_file = fl->fl_file;
>> + if (file_lock_is_thread_owner(new->fl_owner))
>> + new->fl_file = get_file(fl->fl_file);
>> + else
>> + new->fl_file = fl->fl_file;
>> new->fl_ops = fl->fl_ops;
>>
>> if (fl->fl_ops) {
>> @@ -488,13 +493,14 @@ static int flock64_to_posix_lock(struct file *filp, struct file_lock *fl,
>> } else
>> fl->fl_end = OFFSET_MAX;
>>
>> - fl->fl_owner = current->files;
>> + fl->fl_owner = file_lock_make_thread_owner(current->files);
>> fl->fl_pid = current->tgid;
>> - fl->fl_file = filp;
>> + fl->fl_file = get_file(filp);
>> fl->fl_flags = FL_POSIX;
>> fl->fl_ops = NULL;
>> fl->fl_lmops = NULL;
>>
>> +
>> return assign_type(fl, l->l_type);
>> }
>>
>> @@ -2243,6 +2249,7 @@ int fcntl_getlk(struct file *filp, unsigned int cmd, struct flock *flock)
>>
>> fl->fl_flags |= FL_OFDLCK;
>> fl->fl_owner = filp;
>> + fput(filp);
>> }
>>
>> error = vfs_test_lock(filp, fl);
>> @@ -2376,6 +2383,7 @@ int fcntl_setlk(unsigned int fd, struct file *filp, unsigned int cmd,
>> cmd = F_SETLK;
>> file_lock->fl_flags |= FL_OFDLCK;
>> file_lock->fl_owner = filp;
>> + fput(filp);
>> break;
>> case F_OFD_SETLKW:
>> error = -EINVAL;
>> @@ -2385,6 +2393,7 @@ int fcntl_setlk(unsigned int fd, struct file *filp, unsigned int cmd,
>> cmd = F_SETLKW;
>> file_lock->fl_flags |= FL_OFDLCK;
>> file_lock->fl_owner = filp;
>> + fput(filp);
>> fallthrough;
>> case F_SETLKW:
>> file_lock->fl_flags |= FL_SLEEP;
>> @@ -2450,6 +2459,7 @@ int fcntl_getlk64(struct file *filp, unsigned int cmd, struct flock64 *flock)
>> cmd = F_GETLK64;
>> fl->fl_flags |= FL_OFDLCK;
>> fl->fl_owner = filp;
>> + fput(filp);
>> }
>>
>> error = vfs_test_lock(filp, fl);
>> @@ -2499,6 +2509,7 @@ int fcntl_setlk64(unsigned int fd, struct file *filp, unsigned int cmd,
>> cmd = F_SETLK64;
>> file_lock->fl_flags |= FL_OFDLCK;
>> file_lock->fl_owner = filp;
>> + fput(filp);
>> break;
>> case F_OFD_SETLKW:
>> error = -EINVAL;
>> @@ -2508,6 +2519,7 @@ int fcntl_setlk64(unsigned int fd, struct file *filp, unsigned int cmd,
>> cmd = F_SETLKW64;
>> file_lock->fl_flags |= FL_OFDLCK;
>> file_lock->fl_owner = filp;
>> + fput(filp);
>> fallthrough;
>> case F_SETLKW64:
>> file_lock->fl_flags |= FL_SLEEP;
>> diff --git a/include/linux/fs.h b/include/linux/fs.h
>> index e654435f1651..d7d81962a863 100644
>> --- a/include/linux/fs.h
>> +++ b/include/linux/fs.h
>> @@ -1028,6 +1028,20 @@ static inline struct file *get_file(struct file *f)
>> /* legacy typedef, should eventually be removed */
>> typedef void *fl_owner_t;
>>
>> +/*
>> + * Set the last significant bit to 1 to mark that
>> + * we have get a reference of the fl->fl_file.
>> + */
>> +static inline fl_owner_t file_lock_make_thread_owner(fl_owner_t owner)
>> +{
>> + return (fl_owner_t)((unsigned long)owner | 1UL);
>> +}
>> +
>> +static inline bool file_lock_is_thread_owner(fl_owner_t owner)
>> +{
>> + return ((unsigned long)owner & 1UL);
>> +}
>> +
>> struct file_lock;
>>
>> struct file_lock_operations {
>> diff --git a/io_uring/openclose.c b/io_uring/openclose.c
>> index 67178e4bb282..5a12cdf7f8d0 100644
>> --- a/io_uring/openclose.c
>> +++ b/io_uring/openclose.c
>> @@ -212,6 +212,7 @@ int io_close_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
>> int io_close(struct io_kiocb *req, unsigned int issue_flags)
>> {
>> struct files_struct *files = current->files;
>> + fl_owner_t owner = file_lock_make_thread_owner(files);
>> struct io_close *close = io_kiocb_to_cmd(req, struct io_close);
>> struct fdtable *fdt;
>> struct file *file;
>> @@ -247,7 +248,7 @@ int io_close(struct io_kiocb *req, unsigned int issue_flags)
>> goto err;
>>
>> /* No ->flush() or already async, safely close from here */
>> - ret = filp_close(file, current->files);
>> + ret = filp_close(file, owner);
>> err:
>> if (ret < 0)
>> req_set_fail(req);
> I think this is the wrong approach to fixing this. It also looks like
> you could hit a similar problem with OFD locks and this patch wouldn't
> address that issue.
For the OFD locks they will set the 'file' struct as the owner just as
the flock does, it should be okay and I don't think it has this issue if
my understanding is correct here.
> The real bug seems to be that ceph_fl_release_lock dereferences fl_file,
> at a point when it shouldn't rely on that being valid. Most filesystems
> stash some info in fl->fl_u if they need to do bookkeeping after
> releasing a lock. Perhaps ceph should be doing something similar?
This is the 'filp' memory in filp_close(filp, ...):
crash> file.f_path.dentry,f_inode 0xffff952d7ab46200
f_path.dentry = 0xffff9521b121cb40
f_inode = 0xffff951f3ea33550,
We can see the 'f_inode' is pointing to the correct inode memory.
While later in 'ceph_fl_release_lock()':
41 static void ceph_fl_release_lock(struct file_lock *fl)
42 {
43 struct ceph_file_info *fi = fl->fl_file->private_data;
44 struct inode *inode = file_inode(fl->fl_file);
45 struct ceph_inode_info *ci = ceph_inode(inode);
46 atomic_dec(&fi->num_locks);
47 if (atomic_dec_and_test(&ci->i_filelock_ref)) {
48 /* clear error when all locks are released */
49 spin_lock(&ci->i_ceph_lock);
50 ci->i_ceph_flags &= ~CEPH_I_ERROR_FILELOCK;
51 spin_unlock(&ci->i_ceph_lock);
52 }
53 }
It crashed in Line#47 and the 'fl->fl_file' memory is:
crash> file.f_path.dentry,f_inode 0xffff952d4ebd8a00
f_path.dentry = 0x0
f_inode = 0x0,
Please NOTE: the 'filp' and 'fl->fl_file' are two different 'file struct'.
Can we fix this by using 'fl->fl_u' here ?
I was also thinking I could just call the 'get_file(file)' in
ceph_lock() and then in ceph_fl_release_lock() release the reference
counter. How about this ?
Thanks!
- Xiubo
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