4.4-stable review patch. If anyone has any objections, please let me know.
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From: Jiri Kosina jkosina@suse.cz
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.
Signed-off-by: Jiri Kosina jkosina@suse.cz Cc: Andrew Morton akpm@linux-foundation.org Cc: Andy Lutomirski luto@kernel.org Cc: Borislav Petkov bp@alien8.de Cc: Brian Gerst brgerst@gmail.com Cc: Denys Vlasenko dvlasenk@redhat.com Cc: H. Peter Anvin hpa@zytor.com Cc: Josh Poimboeuf jpoimboe@redhat.com Cc: Kees Cook keescook@chromium.org Cc: Linus Torvalds torvalds@linux-foundation.org Cc: Luis R. Rodriguez mcgrof@suse.com Cc: Peter Zijlstra peterz@infradead.org Cc: Thomas Gleixner tglx@linutronix.de Cc: Toshi Kani toshi.kani@hp.com Link: http://lkml.kernel.org/r/alpine.LNX.2.00.1607081137020.24757@cbobk.fhfr.pm Signed-off-by: Ingo Molnar mingo@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- arch/x86/mm/pat.c | 5 +---- drivers/char/mem.c | 6 +----- 2 files changed, 2 insertions(+), 9 deletions(-)
--- a/arch/x86/mm/pat.c +++ b/arch/x86/mm/pat.c @@ -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++; } --- a/drivers/char/mem.c +++ b/drivers/char/mem.c @@ -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++; }