4.19-stable review patch. If anyone has any objections, please let me know.
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From: Mickaël Salaün mic@digikod.net
commit 26f204380a3c182e5adf1a798db0724d6111b597 upstream.
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: stable@vger.kernel.org Cc: Al Viro viro@zeniv.linux.org.uk Cc: Casey Schaufler casey@schaufler-ca.com Cc: Christian Brauner brauner@kernel.org Cc: James Morris jmorris@namei.org Cc: Jann Horn jannh@google.com Cc: Ondrej Mosnacek omosnace@redhat.com Cc: Paul Moore paul@paul-moore.com Cc: Serge E. Hallyn serge@hallyn.com Cc: Stephen Smalley stephen.smalley.work@gmail.com Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Signed-off-by: Mickaël Salaün mic@digikod.net Signed-off-by: Paul Moore paul@paul-moore.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- fs/fcntl.c | 14 ++++---------- 1 file changed, 4 insertions(+), 10 deletions(-)
--- a/fs/fcntl.c +++ b/fs/fcntl.c @@ -84,8 +84,8 @@ static int setfl(int fd, struct file * f return error; }
-static void f_modown(struct file *filp, struct pid *pid, enum pid_type type, - int force) +void __f_setown(struct file *filp, struct pid *pid, enum pid_type type, + int force) { write_lock_irq(&filp->f_owner.lock); if (force || !filp->f_owner.pid) { @@ -95,19 +95,13 @@ static void f_modown(struct file *filp,
if (pid) { const struct cred *cred = current_cred(); + security_file_set_fowner(filp); filp->f_owner.uid = cred->uid; filp->f_owner.euid = cred->euid; } } write_unlock_irq(&filp->f_owner.lock); } - -void __f_setown(struct file *filp, struct pid *pid, enum pid_type type, - int force) -{ - security_file_set_fowner(filp); - f_modown(filp, pid, type, force); -} EXPORT_SYMBOL(__f_setown);
int f_setown(struct file *filp, unsigned long arg, int force) @@ -143,7 +137,7 @@ EXPORT_SYMBOL(f_setown);
void f_delown(struct file *filp) { - f_modown(filp, NULL, PIDTYPE_TGID, 1); + __f_setown(filp, NULL, PIDTYPE_TGID, 1); }
pid_t f_getown(struct file *filp)