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pidfs: improve ioctl handling

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Pidfs supports extensible and non-extensible ioctls. The extensible
ioctls need to check for the ioctl number itself not just the ioctl
command otherwise both backward- and forward compatibility are broken.

The pidfs ioctl handler also needs to look at the type of the ioctl
command to guard against cases where "[...] a daemon receives some
random file descriptor from a (potentially less privileged) client and
expects the FD to be of some specific type, it might call ioctl() on
this FD with some type-specific command and expect the call to fail if
the FD is of the wrong type; but due to the missing type check, the
kernel instead performs some action that userspace didn't expect."
(cf. [1]]

Link: https://lore.kernel.org/r/20250204-work-pidfs-ioctl-v1-1-04987d239575@kernel.org
Link: https://lore.kernel.org/r/CAG48ez2K9A5GwtgqO31u9ZL292we8ZwAA=TJwwEv7wRuJ3j4Lw@mail.gmail.com [1]
Fixes: 8ce3528188 ("pidfs: check for valid ioctl commands")
Acked-by: Luca Boccassi <luca.boccassi@gmail.com>
Reported-by: Jann Horn <jannh@google.com>
Cc: stable@vger.kernel.org # v6.13; please backport with 8ce3528188 ("pidfs: check for valid ioctl commands")
Signed-off-by: Christian Brauner <brauner@kernel.org>
This commit is contained in:
Christian Brauner 2025-02-04 14:51:20 +01:00
parent ec6164adc7
commit 091ee63e36
No known key found for this signature in database
GPG key ID: 91C61BC06578DCA2
1 changed files with 11 additions and 1 deletions

12
fs/pidfs.c
View file

@ -287,7 +287,6 @@ static bool pidfs_ioctl_valid(unsigned int cmd)
switch (cmd) {
case FS_IOC_GETVERSION:
case PIDFD_GET_CGROUP_NAMESPACE:
case PIDFD_GET_INFO:
case PIDFD_GET_IPC_NAMESPACE:
case PIDFD_GET_MNT_NAMESPACE:
case PIDFD_GET_NET_NAMESPACE:
@ -300,6 +299,17 @@ static bool pidfs_ioctl_valid(unsigned int cmd)
return true;
}
/* Extensible ioctls require some more careful checks. */
switch (_IOC_NR(cmd)) {
case _IOC_NR(PIDFD_GET_INFO):
/*
* Try to prevent performing a pidfd ioctl when someone
* erronously mistook the file descriptor for a pidfd.
* This is not perfect but will catch most cases.
*/
return (_IOC_TYPE(cmd) == _IOC_TYPE(PIDFD_GET_INFO));
}
return false;
}