4.4-stable review patch. If anyone has any objections, please let me know. ------------------ From: Jiri Kosina <jkosina@xxxxxxx> 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@xxxxxxx> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Cc: Andy Lutomirski <luto@xxxxxxxxxx> Cc: Borislav Petkov <bp@xxxxxxxxx> Cc: Brian Gerst <brgerst@xxxxxxxxx> Cc: Denys Vlasenko <dvlasenk@xxxxxxxxxx> Cc: H. Peter Anvin <hpa@xxxxxxxxx> Cc: Josh Poimboeuf <jpoimboe@xxxxxxxxxx> Cc: Kees Cook <keescook@xxxxxxxxxxxx> Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Cc: Luis R. Rodriguez <mcgrof@xxxxxxxx> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Cc: Toshi Kani <toshi.kani@xxxxxx> Link: http://lkml.kernel.org/r/alpine.LNX.2.00.1607081137020.24757@xxxxxxxxxxxxx Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- 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++; }