From: David Howells dhowells@redhat.com
[ Upstream commit 29e44f4535faa71a70827af3639b5e6762d8f02a ]
Impose a limit on the number of watches that a user can hold so that they can't use this mechanism to fill up all the available memory.
This is done by putting a counter in user_struct that's incremented when a watch is allocated and decreased when it is released. If the number exceeds the RLIMIT_NOFILE limit, the watch is rejected with EAGAIN.
This can be tested by the following means:
(1) Create a watch queue and attach it to fd 5 in the program given - in this case, bash:
keyctl watch_session /tmp/nlog /tmp/gclog 5 bash
(2) In the shell, set the maximum number of files to, say, 99:
ulimit -n 99
(3) Add 200 keyrings:
for ((i=0; i<200; i++)); do keyctl newring a$i @s || break; done
(4) Try to watch all of the keyrings:
for ((i=0; i<200; i++)); do echo $i; keyctl watch_add 5 %:a$i || break; done
This should fail when the number of watches belonging to the user hits 99.
(5) Remove all the keyrings and all of those watches should go away:
for ((i=0; i<200; i++)); do keyctl unlink %:a$i; done
(6) Kill off the watch queue by exiting the shell spawned by watch_session.
Fixes: c73be61cede5 ("pipe: Add general notification queue support") Reported-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: David Howells dhowells@redhat.com Reviewed-by: Jarkko Sakkinen jarkko.sakkinen@linux.intel.com Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Sasha Levin sashal@kernel.org --- include/linux/sched/user.h | 3 +++ kernel/watch_queue.c | 8 ++++++++ 2 files changed, 11 insertions(+)
diff --git a/include/linux/sched/user.h b/include/linux/sched/user.h index 917d88edb7b9d..a8ec3b6093fcb 100644 --- a/include/linux/sched/user.h +++ b/include/linux/sched/user.h @@ -36,6 +36,9 @@ struct user_struct { defined(CONFIG_NET) || defined(CONFIG_IO_URING) atomic_long_t locked_vm; #endif +#ifdef CONFIG_WATCH_QUEUE + atomic_t nr_watches; /* The number of watches this user currently has */ +#endif
/* Miscellaneous per-user rate limit */ struct ratelimit_state ratelimit; diff --git a/kernel/watch_queue.c b/kernel/watch_queue.c index f74020f6bd9d5..0ef8f65bd2d71 100644 --- a/kernel/watch_queue.c +++ b/kernel/watch_queue.c @@ -393,6 +393,7 @@ static void free_watch(struct rcu_head *rcu) struct watch *watch = container_of(rcu, struct watch, rcu);
put_watch_queue(rcu_access_pointer(watch->queue)); + atomic_dec(&watch->cred->user->nr_watches); put_cred(watch->cred); }
@@ -452,6 +453,13 @@ int add_watch_to_object(struct watch *watch, struct watch_list *wlist) watch->cred = get_current_cred(); rcu_assign_pointer(watch->watch_list, wlist);
+ if (atomic_inc_return(&watch->cred->user->nr_watches) > + task_rlimit(current, RLIMIT_NOFILE)) { + atomic_dec(&watch->cred->user->nr_watches); + put_cred(watch->cred); + return -EAGAIN; + } + spin_lock_bh(&wqueue->lock); kref_get(&wqueue->usage); kref_get(&watch->usage);