| Message ID | 159562904644.2287160.13294507067766261970.stgit@warthog.procyon.org.uk (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | watch_queue: Limit the number of watches a user can hold | expand |
On Fri, Jul 24, 2020 at 11:17:26PM +0100, David Howells wrote: > 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> > --- > > 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 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; > diff --git a/kernel/watch_queue.c b/kernel/watch_queue.c > index f74020f6bd9d..0ef8f65bd2d7 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); > > Reviewed-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com> David, BTW, would it be possible to push keyrings to lore.kernel.org? I don't have an archive for keyrings, which means that I cannot push this forward. /Jarkko
Hi Linus, Could you consider taking this patch as a bugfix since the problem exists already in upstream code? David
David Howells <dhowells@redhat.com> wrote: > Could you consider taking this patch as a bugfix since the problem exists > already in upstream code? Alternatively, I can include it in a set with the mount notifications. David
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; diff --git a/kernel/watch_queue.c b/kernel/watch_queue.c index f74020f6bd9d..0ef8f65bd2d7 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);
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> --- include/linux/sched/user.h | 3 +++ kernel/watch_queue.c | 8 ++++++++ 2 files changed, 11 insertions(+)