Patch "x86/mm/pat, /dev/mem: Remove superfluous error message" has been added to the 4.4-stable tree

This is a note to let you know that I've just added the patch titled

x86/mm/pat, /dev/mem: Remove superfluous error message

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
x86-mm-pat-dev-mem-remove-superfluous-error-message.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Jiri Kosina <[email protected]>
Date: Fri, 8 Jul 2016 11:38:28 +0200
Subject: x86/mm/pat, /dev/mem: Remove superfluous error message

From: Jiri Kosina <[email protected]>

commit 39380b80d72723282f0ea1d1bbf2294eae45013e upstream.

Currently it's possible for broken (or malicious) userspace to flood a kernel log indefinitely with messages a-la

	Program dmidecode tried to access /dev/mem between f0000->100000

because range_is_allowed() is case of CONFIG_STRICT_DEVMEM being turned on dumps this information each and every time devmem_is_allowed() fails.

Reportedly userspace that is able to trigger contignuous flow of these messages exists.

It would be possible to rate limit this message, but that'd have a questionable value; the administrator wouldn't get information about all the failing accessess, so then the information would be both superfluous and incomplete at the same time :)

Returning EPERM (which is what is actually happening) is enough indication for userspace what has happened; no need to log this particular error as some sort of special condition.

---
 arch/x86/mm/pat.c  |    5 +----
 drivers/char/mem.c |    6 +-----
 2 files changed, 2 insertions(+), 9 deletions(-)

@@ -750,11 +750,8 @@ static inline int range_is_allowed(unsig
 		return 1;
 
 	while (cursor < to) {
-		if (!devmem_is_allowed(pfn)) {
-			pr_info("x86/PAT: Program %s tried to access /dev/mem between [mem %#010Lx-%#010Lx], PAT prevents it\n",
-				current->comm, from, to - 1);
+		if (!devmem_is_allowed(pfn))
 			return 0;
-		}
 		cursor += PAGE_SIZE;
 		pfn++;
 	}

@@ -70,12 +70,8 @@ static inline int range_is_allowed(unsig
 	u64 cursor = from;
 
 	while (cursor < to) {
-		if (!devmem_is_allowed(pfn)) {
-			printk(KERN_INFO
-		"Program %s tried to access /dev/mem between %Lx->%Lx.\n",
-				current->comm, from, to);
+		if (!devmem_is_allowed(pfn))
 			return 0;
-		}
 		cursor += PAGE_SIZE;
 		pfn++;
 	}

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/x86-mm-pat-dev-mem-remove-superfluous-error-message.patch