This is a note to let you know that I've just added the patch titled
fanotify: fix permission model of unprivileged group
to the 5.10-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
fanotify-fix-permission-model-of-unprivileged-group.patch
and it can be found in the queue-5.10 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 34eb839d60a1045b3867dd7f1a2a227c68f00ab9
Author: Amir Goldstein <amir73il@xxxxxxxxx>
Date: Mon May 24 16:53:21 2021 +0300
fanotify: fix permission model of unprivileged group
[ Upstream commit a8b98c808eab3ec8f1b5a64be967b0f4af4cae43 ]
Reporting event->pid should depend on the privileges of the user that
initialized the group, not the privileges of the user reading the
events.
Use an internal group flag FANOTIFY_UNPRIV to record the fact that the
group was initialized by an unprivileged user.
To be on the safe side, the premissions to setup filesystem and mount
marks now require that both the user that initialized the group and
the user setting up the mark have CAP_SYS_ADMIN.
Link: https://lore.kernel.org/linux-fsdevel/CAOQ4uxiA77_P5vtv7e83g0+9d7B5W9ZTE4GfQEYbWmfT1rA=VA@xxxxxxxxxxxxxx/
Fixes: 7cea2a3c505e ("fanotify: support limited functionality for unprivileged users")
Cc: <Stable@xxxxxxxxxxxxxxx> # v5.12+
Link: https://lore.kernel.org/r/20210524135321.2190062-1-amir73il@xxxxxxxxx
Reviewed-by: Matthew Bobrowski <repnop@xxxxxxxxxx>
Acked-by: Christian Brauner <christian.brauner@xxxxxxxxxx>
Signed-off-by: Amir Goldstein <amir73il@xxxxxxxxx>
Signed-off-by: Jan Kara <jack@xxxxxxx>
Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/fs/notify/fanotify/fanotify_user.c b/fs/notify/fanotify/fanotify_user.c
index 98289ace66fac..1c439e2fdcd80 100644
--- a/fs/notify/fanotify/fanotify_user.c
+++ b/fs/notify/fanotify/fanotify_user.c
@@ -424,11 +424,18 @@ static ssize_t copy_event_to_user(struct fsnotify_group *group,
* events generated by the listener process itself, without disclosing
* the pids of other processes.
*/
- if (!capable(CAP_SYS_ADMIN) &&
+ if (FAN_GROUP_FLAG(group, FANOTIFY_UNPRIV) &&
task_tgid(current) != event->pid)
metadata.pid = 0;
- if (path && path->mnt && path->dentry) {
+ /*
+ * For now, fid mode is required for an unprivileged listener and
+ * fid mode does not report fd in events. Keep this check anyway
+ * for safety in case fid mode requirement is relaxed in the future
+ * to allow unprivileged listener to get events with no fd and no fid.
+ */
+ if (!FAN_GROUP_FLAG(group, FANOTIFY_UNPRIV) &&
+ path && path->mnt && path->dentry) {
fd = create_fd(group, path, &f);
if (fd < 0)
return fd;
@@ -1040,6 +1047,7 @@ SYSCALL_DEFINE2(fanotify_init, unsigned int, flags, unsigned int, event_f_flags)
int f_flags, fd;
unsigned int fid_mode = flags & FANOTIFY_FID_BITS;
unsigned int class = flags & FANOTIFY_CLASS_BITS;
+ unsigned int internal_flags = 0;
pr_debug("%s: flags=%x event_f_flags=%x\n",
__func__, flags, event_f_flags);
@@ -1053,6 +1061,13 @@ SYSCALL_DEFINE2(fanotify_init, unsigned int, flags, unsigned int, event_f_flags)
*/
if ((flags & FANOTIFY_ADMIN_INIT_FLAGS) || !fid_mode)
return -EPERM;
+
+ /*
+ * Setting the internal flag FANOTIFY_UNPRIV on the group
+ * prevents setting mount/filesystem marks on this group and
+ * prevents reporting pid and open fd in events.
+ */
+ internal_flags |= FANOTIFY_UNPRIV;
}
#ifdef CONFIG_AUDITSYSCALL
@@ -1105,7 +1120,7 @@ SYSCALL_DEFINE2(fanotify_init, unsigned int, flags, unsigned int, event_f_flags)
goto out_destroy_group;
}
- group->fanotify_data.flags = flags;
+ group->fanotify_data.flags = flags | internal_flags;
group->memcg = get_mem_cgroup_from_mm(current->mm);
group->fanotify_data.merge_hash = fanotify_alloc_merge_hash();
@@ -1323,11 +1338,13 @@ static int do_fanotify_mark(int fanotify_fd, unsigned int flags, __u64 mask,
group = f.file->private_data;
/*
- * An unprivileged user is not allowed to watch a mount point nor
- * a filesystem.
+ * An unprivileged user is not allowed to setup mount nor filesystem
+ * marks. This also includes setting up such marks by a group that
+ * was initialized by an unprivileged user.
*/
ret = -EPERM;
- if (!capable(CAP_SYS_ADMIN) &&
+ if ((!capable(CAP_SYS_ADMIN) ||
+ FAN_GROUP_FLAG(group, FANOTIFY_UNPRIV)) &&
mark_type != FAN_MARK_INODE)
goto fput_and_out;
@@ -1478,6 +1495,7 @@ static int __init fanotify_user_setup(void)
max_marks = clamp(max_marks, FANOTIFY_OLD_DEFAULT_MAX_MARKS,
FANOTIFY_DEFAULT_MAX_USER_MARKS);
+ BUILD_BUG_ON(FANOTIFY_INIT_FLAGS & FANOTIFY_INTERNAL_GROUP_FLAGS);
BUILD_BUG_ON(HWEIGHT32(FANOTIFY_INIT_FLAGS) != 10);
BUILD_BUG_ON(HWEIGHT32(FANOTIFY_MARK_FLAGS) != 9);
diff --git a/fs/notify/fdinfo.c b/fs/notify/fdinfo.c
index 85b112bd88511..3451708fd035c 100644
--- a/fs/notify/fdinfo.c
+++ b/fs/notify/fdinfo.c
@@ -137,7 +137,7 @@ void fanotify_show_fdinfo(struct seq_file *m, struct file *f)
struct fsnotify_group *group = f->private_data;
seq_printf(m, "fanotify flags:%x event-flags:%x\n",
- group->fanotify_data.flags,
+ group->fanotify_data.flags & FANOTIFY_INIT_FLAGS,
group->fanotify_data.f_flags);
show_fdinfo(m, f, fanotify_fdinfo);
diff --git a/include/linux/fanotify.h b/include/linux/fanotify.h
index bad41bcb25dfb..a16dbeced1528 100644
--- a/include/linux/fanotify.h
+++ b/include/linux/fanotify.h
@@ -51,6 +51,10 @@ extern struct ctl_table fanotify_table[]; /* for sysctl */
#define FANOTIFY_INIT_FLAGS (FANOTIFY_ADMIN_INIT_FLAGS | \
FANOTIFY_USER_INIT_FLAGS)
+/* Internal group flags */
+#define FANOTIFY_UNPRIV 0x80000000
+#define FANOTIFY_INTERNAL_GROUP_FLAGS (FANOTIFY_UNPRIV)
+
#define FANOTIFY_MARK_TYPE_BITS (FAN_MARK_INODE | FAN_MARK_MOUNT | \
FAN_MARK_FILESYSTEM)
