From 29e44f4535faa71a70827af3639b5e6762d8f02a Mon Sep 17 00:00:00 2001 From: David Howells Date: Mon, 17 Aug 2020 11:07:28 +0100 Subject: watch_queue: Limit the number of watches a user can hold 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 Signed-off-by: David Howells Reviewed-by: Jarkko Sakkinen Signed-off-by: Linus Torvalds --- include/linux/sched/user.h | 3 +++ 1 file changed, 3 insertions(+) (limited to 'include') diff --git a/include/linux/sched/user.h b/include/linux/sched/user.h index 917d88edb7b9..a8ec3b6093fc 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; -- cgit v1.2.3-59-g8ed1b