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/internal.h | |
| 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/internal.h')
| -rw-r--r-- | fs/internal.h | 10 |
1 files changed, 10 insertions, 0 deletions
diff --git a/fs/internal.h b/fs/internal.h index 87e96b9024ce..31861e6c3eff 100644 --- a/fs/internal.h +++ b/fs/internal.h @@ -101,6 +101,16 @@ 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 */ |