Thread A trying to acquire a write lease checks the value of i_readcount
and i_writecount in check_conflicting_open() to verify that its own fd
is the only fd referencing the file.
Thread B trying to open the file for read will call break_lease() in
do_dentry_open() before incrementing i_readcount, which leaves a small
window where thread A can acquire the write lease and then thread B
completes the open of the file for read without breaking the write lease
that was acquired by thread A.
Fix this race by incrementing i_readcount before checking for existing
leases, same as the case with i_writecount.
Use a helper put_file_access() to decrement i_readcount or i_writecount
in do_dentry_open() and __fput().
Fixes: 387e3746d01c ("locks: eliminate false positive conflicts for write lease")
Signed-off-by: Amir Goldstein <amir73il@xxxxxxxxx>
---
Hi Jeff,
This fixes a race I found during code audit - I do not have a reproducer
for it.
I ran the fstests I found for locks and leases:
generic/131 generic/478 generic/504 generic/571
and the LTP fcntl tests.
Encountered this warning with generic/131, but I also see it on
current master:
=============================
WARNING: suspicious RCU usage
5.19.0-xfstests-14277-gbd6ab3ef4e93 #966 Not tainted
-----------------------------
include/net/sock.h:592 suspicious rcu_dereference_check() usage!
other info that might help us debug this:
rcu_scheduler_active = 2, debug_locks = 1
5 locks held by locktest/3996:
#0: ffff88800be1d7a0 (&sb->s_type->i_mutex_key#8){+.+.}-{3:3}, at: __sock_release+0x25/0x97
#1: ffff88800909ce00 (sk_lock-AF_INET){+.+.}-{0:0}, at: tcp_close+0x14/0x60
#2: ffff888006847cc8 (&h->lhash2[i].lock){+.+.}-{2:2}, at: inet_unhash+0x3a/0xcf
#3: ffffffff82a8ac18 (reuseport_lock){+...}-{2:2}, at: reuseport_detach_sock+0x17/0xb8
#4: ffff88800909d0b0 (clock-AF_INET){++..}-{2:2}, at: bpf_sk_reuseport_detach+0x1b/0x85
stack backtrace:
CPU: 1 PID: 3996 Comm: locktest Not tainted 5.19.0-xfstests-14277-gbd6ab3ef4e93 #966
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.13.0-1ubuntu1.1 04/01/2014
Call Trace:
<TASK>
dump_stack_lvl+0x45/0x5d
bpf_sk_reuseport_detach+0x5c/0x85
reuseport_detach_sock+0x65/0xb8
inet_unhash+0x55/0xcf
tcp_set_state+0xb3/0x10d
? mark_lock.part.0+0x30/0x101
__tcp_close+0x26/0x32d
tcp_close+0x20/0x60
inet_release+0x50/0x64
__sock_release+0x32/0x97
sock_close+0x14/0x1b
__fput+0x118/0x1eb
Let me know what you think.
Thanks,
Amir.
fs/file_table.c | 7 +------
fs/open.c | 11 ++++-------
include/linux/fs.h | 10 ++++++++++
3 files changed, 15 insertions(+), 13 deletions(-)
diff --git a/fs/file_table.c b/fs/file_table.c
index 99c6796c9f28..dd88701e54a9 100644
--- a/fs/file_table.c
+++ b/fs/file_table.c
@@ -324,12 +324,7 @@ static void __fput(struct file *file)
}
fops_put(file->f_op);
put_pid(file->f_owner.pid);
- if ((mode & (FMODE_READ | FMODE_WRITE)) == FMODE_READ)
- i_readcount_dec(inode);
- if (mode & FMODE_WRITER) {
- put_write_access(inode);
- __mnt_drop_write(mnt);
- }
+ put_file_access(file);
dput(dentry);
if (unlikely(mode & FMODE_NEED_UNMOUNT))
dissolve_on_fput(mnt);
diff --git a/fs/open.c b/fs/open.c
index 8a813fa5ca56..a98572585815 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -840,7 +840,9 @@ static int do_dentry_open(struct file *f,
return 0;
}
- if (f->f_mode & FMODE_WRITE && !special_file(inode->i_mode)) {
+ if ((f->f_mode & (FMODE_READ | FMODE_WRITE)) == FMODE_READ) {
+ i_readcount_inc(inode);
+ } else if (f->f_mode & FMODE_WRITE && !special_file(inode->i_mode)) {
error = get_write_access(inode);
if (unlikely(error))
goto cleanup_file;
@@ -880,8 +882,6 @@ static int do_dentry_open(struct file *f,
goto cleanup_all;
}
f->f_mode |= FMODE_OPENED;
- if ((f->f_mode & (FMODE_READ | FMODE_WRITE)) == FMODE_READ)
- i_readcount_inc(inode);
if ((f->f_mode & FMODE_READ) &&
likely(f->f_op->read || f->f_op->read_iter))
f->f_mode |= FMODE_CAN_READ;
@@ -935,10 +935,7 @@ static int do_dentry_open(struct file *f,
if (WARN_ON_ONCE(error > 0))
error = -EINVAL;
fops_put(f->f_op);
- if (f->f_mode & FMODE_WRITER) {
- put_write_access(inode);
- __mnt_drop_write(f->f_path.mnt);
- }
+ put_file_access(f);
cleanup_file:
path_put(&f->f_path);
f->f_path.mnt = NULL;
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 9eced4cc286e..8bc04852c3da 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -3000,6 +3000,16 @@ static inline void i_readcount_inc(struct inode *inode)
return;
}
#endif
+static inline void put_file_access(struct file *file)
+{
+ if ((file->f_mode & (FMODE_READ | FMODE_WRITE)) == FMODE_READ) {
+ i_readcount_dec(file->f_inode);
+ } else if (file->f_mode & FMODE_WRITER) {
+ put_write_access(file->f_inode);
+ __mnt_drop_write(file->f_path.mnt);
+ }
+}
+
extern int do_pipe_flags(int *, int);
extern ssize_t kernel_read(struct file *, void *, size_t, loff_t *);
--
2.25.1
