diff options
| author | Amir Goldstein <amir73il@gmail.com> | 2022-08-16 17:53:17 +0300 |
|---|---|---|
| committer | Al Viro <viro@zeniv.linux.org.uk> | 2022-08-16 10:59:54 -0400 |
| commit | d6da19c9cace63290ccfccb1fc35151ffefc0bec (patch) | |
| tree | 00e66911e1e16675007d324b91572ab73adac346 /fs/open.c | |
| parent | 568035b01cfb107af8d2e4bd2fb9aea22cf5b868 (diff) | |
locks: fix TOCTOU race when granting write lease
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>
Diffstat (limited to 'fs/open.c')
| -rw-r--r-- | fs/open.c | 11 |
1 files changed, 4 insertions, 7 deletions
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 @@ cleanup_all: 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; |