fs: Fix file_set_fowner LSM hook inconsistencies

The fcntl's F_SETOWN command sets the process that handle SIGIO/SIGURG
for the related file descriptor.  Before this change, the
file_set_fowner LSM hook was always called, ignoring the VFS logic which
may not actually change the process that handles SIGIO (e.g. TUN, TTY,
dnotify), nor update the related UID/EUID.

Moreover, because security_file_set_fowner() was called without lock
(e.g. f_owner.lock), concurrent F_SETOWN commands could result to a race
condition and inconsistent LSM states (e.g. SELinux's fown_sid) compared
to struct fown_struct's UID/EUID.

This change makes sure the LSM states are always in sync with the VFS
state by moving the security_file_set_fowner() call close to the
UID/EUID updates and using the same f_owner.lock .

Rename f_modown() to __f_setown() to simplify code.

Cc: [email protected]
Cc: Al Viro <[email protected]>
Cc: Casey Schaufler <[email protected]>
Cc: Christian Brauner <[email protected]>
Cc: James Morris <[email protected]>
Cc: Jann Horn <[email protected]>
Cc: Ondrej Mosnacek <[email protected]>
Cc: Paul Moore <[email protected]>
Cc: Serge E. Hallyn <[email protected]>
Cc: Stephen Smalley <[email protected]>
Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Mickaël Salaün <[email protected]>
Signed-off-by: Paul Moore <[email protected]>

0 files changed, 0 insertions, 0 deletions