From: Amir Goldstein amir73il@gmail.com
[ Upstream commit d6da19c9cace63290ccfccb1fc35151ffefc0bec ]
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") Reviewed-by: Jeff Layton jlayton@kernel.org Signed-off-by: Amir Goldstein amir73il@gmail.com Signed-off-by: Al Viro viro@zeniv.linux.org.uk Signed-off-by: Sasha Levin sashal@kernel.org --- fs/file_table.c | 7 +------ fs/internal.h | 10 ++++++++++ fs/open.c | 11 ++++------- 3 files changed, 15 insertions(+), 13 deletions(-)
diff --git a/fs/file_table.c b/fs/file_table.c index 5424e3a8df5f..543a501b0247 100644 --- a/fs/file_table.c +++ b/fs/file_table.c @@ -321,12 +321,7 @@ 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/internal.h b/fs/internal.h index 3e206d3e317c..4372d67a3753 100644 --- a/fs/internal.h +++ b/fs/internal.h @@ -102,6 +102,16 @@ extern void chroot_fs_refs(const struct path *, const struct path *); extern struct file *alloc_empty_file(int, const struct cred *); extern struct file *alloc_empty_file_noaccount(int, const struct cred *);
+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); + } +} + /* * super.c */ diff --git a/fs/open.c b/fs/open.c index 1d57fbde2feb..5874258b54bd 100644 --- a/fs/open.c +++ b/fs/open.c @@ -810,7 +810,9 @@ 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; @@ -850,8 +852,6 @@ 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; @@ -902,10 +902,7 @@ 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;