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authorDavide Libenzi <davidel@xmailserver.org>2008-12-01 13:13:55 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2008-12-01 19:55:24 -0800
commit7ef9964e6d1b911b78709f144000aacadd0ebc21 (patch)
tree30667d0a2f8e53973ff48d2c02df48bbc6fe74aa /kernel/sysctl.c
parentb7d271df873c5121a4ca1c70dea126b5920ec2f1 (diff)
epoll: introduce resource usage limits
It has been thought that the per-user file descriptors limit would also limit the resources that a normal user can request via the epoll interface. Vegard Nossum reported a very simple program (a modified version attached) that can make a normal user to request a pretty large amount of kernel memory, well within the its maximum number of fds. To solve such problem, default limits are now imposed, and /proc based configuration has been introduced. A new directory has been created, named /proc/sys/fs/epoll/ and inside there, there are two configuration points: max_user_instances = Maximum number of devices - per user max_user_watches = Maximum number of "watched" fds - per user The current default for "max_user_watches" limits the memory used by epoll to store "watches", to 1/32 of the amount of the low RAM. As example, a 256MB 32bit machine, will have "max_user_watches" set to roughly 90000. That should be enough to not break existing heavy epoll users. The default value for "max_user_instances" is set to 128, that should be enough too. This also changes the userspace, because a new error code can now come out from EPOLL_CTL_ADD (-ENOSPC). The EMFILE from epoll_create() was already listed, so that should be ok. [akpm@linux-foundation.org: use get_current_user()] Signed-off-by: Davide Libenzi <davidel@xmailserver.org> Cc: Michael Kerrisk <mtk.manpages@gmail.com> Cc: <stable@kernel.org> Cc: Cyrill Gorcunov <gorcunov@gmail.com> Reported-by: Vegard Nossum <vegardno@ifi.uio.no> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'kernel/sysctl.c')
-rw-r--r--kernel/sysctl.c10
1 files changed, 10 insertions, 0 deletions
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 9d048fa2d90..3d56fe7570d 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -176,6 +176,9 @@ extern struct ctl_table random_table[];
#ifdef CONFIG_INOTIFY_USER
extern struct ctl_table inotify_table[];
#endif
+#ifdef CONFIG_EPOLL
+extern struct ctl_table epoll_table[];
+#endif
#ifdef HAVE_ARCH_PICK_MMAP_LAYOUT
int sysctl_legacy_va_layout;
@@ -1325,6 +1328,13 @@ static struct ctl_table fs_table[] = {
.child = inotify_table,
},
#endif
+#ifdef CONFIG_EPOLL
+ {
+ .procname = "epoll",
+ .mode = 0555,
+ .child = epoll_table,
+ },
+#endif
#endif
{
.ctl_name = KERN_SETUID_DUMPABLE,