From bef3efbeb897b56867e271cdbc5f8adaacaeb9cd Mon Sep 17 00:00:00 2001 From: "Luck, Tony" Date: Thu, 22 Feb 2018 09:15:06 -0800 Subject: efivarfs: Limit the rate for non-root to read files Each read from a file in efivarfs results in two calls to EFI (one to get the file size, another to get the actual data). On X86 these EFI calls result in broadcast system management interrupts (SMI) which affect performance of the whole system. A malicious user can loop performing reads from efivarfs bringing the system to its knees. Linus suggested per-user rate limit to solve this. So we add a ratelimit structure to "user_struct" and initialize it for the root user for no limit. When allocating user_struct for other users we set the limit to 100 per second. This could be used for other places that want to limit the rate of some detrimental user action. In efivarfs if the limit is exceeded when reading, we take an interruptible nap for 50ms and check the rate limit again. Signed-off-by: Tony Luck Acked-by: Ard Biesheuvel Signed-off-by: Linus Torvalds --- fs/efivarfs/file.c | 6 ++++++ 1 file changed, 6 insertions(+) (limited to 'fs/efivarfs') diff --git a/fs/efivarfs/file.c b/fs/efivarfs/file.c index 5f22e74bbade..8e568428c88b 100644 --- a/fs/efivarfs/file.c +++ b/fs/efivarfs/file.c @@ -8,6 +8,7 @@ */ #include +#include #include #include #include @@ -74,6 +75,11 @@ static ssize_t efivarfs_file_read(struct file *file, char __user *userbuf, ssize_t size = 0; int err; + while (!__ratelimit(&file->f_cred->user->ratelimit)) { + if (!msleep_interruptible(50)) + return -EINTR; + } + err = efivar_entry_size(var, &datasize); /* -- cgit