summaryrefslogtreecommitdiffstats
path: root/include
diff options
context:
space:
mode:
authorDavid Howells <dhowells@redhat.com>2020-08-17 11:07:28 +0100
committerLinus Torvalds <torvalds@linux-foundation.org>2020-08-17 09:39:18 -0700
commit29e44f4535faa71a70827af3639b5e6762d8f02a (patch)
tree4775719cd867602b8aea88ac16f4d627d1a122e5 /include
parent9123e3a74ec7b934a4a099e98af6a61c2f80bbf5 (diff)
downloadlinux-stable-29e44f4535faa71a70827af3639b5e6762d8f02a.tar.gz
linux-stable-29e44f4535faa71a70827af3639b5e6762d8f02a.tar.bz2
linux-stable-29e44f4535faa71a70827af3639b5e6762d8f02a.zip
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 <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>
Diffstat (limited to 'include')
-rw-r--r--include/linux/sched/user.h3
1 files changed, 3 insertions, 0 deletions
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;