diff options
| author | Amir Goldstein <amir73il@gmail.com> | 2022-08-16 17:53:17 +0300 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2022-10-26 12:34:58 +0200 |
| commit | a29b6eb959bd5c3cbb2dd0ed7c982a10c93734d4 (patch) | |
| tree | a469a00152582163dfe7c7ba3680f43f87a265bf /fs | |
| parent | 7e053784c4c70df28324106d476778be7a4519b3 (diff) | |
locks: fix TOCTOU race when granting write lease
[ 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>
Diffstat (limited to 'fs')
| -rw-r--r-- | fs/file_table.c | 7 | ||||
| -rw-r--r-- | fs/internal.h | 10 | ||||
| -rw-r--r-- | fs/open.c | 11 |
3 files changed, 15 insertions, 13 deletions
diff --git a/fs/file_table.c b/fs/file_table.c index e8c9016703ad..6f297f9782fc 100644 --- a/fs/file_table.c +++ b/fs/file_table.c @@ -284,12 +284,7 @@ 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 4f1fe6d08866..9075490f21a6 100644 --- a/fs/internal.h +++ b/fs/internal.h @@ -100,6 +100,16 @@ 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 1ba1d2ab2ef0..5e322f188e83 100644 --- a/fs/open.c +++ b/fs/open.c @@ -786,7 +786,9 @@ 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; @@ -826,8 +828,6 @@ 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; @@ -880,10 +880,7 @@ 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; |