From 148a1bc84398039e2b96ff78678c4d9a67f81452 Mon Sep 17 00:00:00 2001 From: Robin Murphy Date: Wed, 1 Jun 2016 19:21:42 +0100 Subject: [PATCH] drivers: char: mem: Check {read,write}_kmem() addresses Arriving at read_kmem() with an offset representing a bogus kernel address (e.g. 0 from a simple "cat /dev/kmem") leads to copy_to_user faulting on the kernel-side read. x86_64 happens to get away with this since the optimised implementation uses "rep movs*", thus the user write (which is allowed to fault) and the kernel read are the same instruction, the kernel-side fault falls into the user-side fixup handler and the chain of events which transpires ends up returning an error as one might expect, even if it's an inappropriate -EFAULT. On other architectures, though, the read is not covered by the fixup entry for the write, and we get a big scary "Unable to hande kernel paging request..." dump. The more typical use-case of mmap_kmem() has always (within living memory at least) returned -EIO for addresses which don't satisfy pfn_valid(), so let's make that consistent across {read,write}_kem() too. Reported-by: Kefeng Wang Signed-off-by: Robin Murphy Signed-off-by: Greg Kroah-Hartman --- drivers/char/mem.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/drivers/char/mem.c b/drivers/char/mem.c index a33163dbb913..5bb1985ec484 100644 --- a/drivers/char/mem.c +++ b/drivers/char/mem.c @@ -381,6 +381,9 @@ static ssize_t read_kmem(struct file *file, char __user *buf, char *kbuf; /* k-addr because vread() takes vmlist_lock rwlock */ int err = 0; + if (!pfn_valid(PFN_DOWN(p))) + return -EIO; + read = 0; if (p < (unsigned long) high_memory) { low_count = count; @@ -509,6 +512,9 @@ static ssize_t write_kmem(struct file *file, const char __user *buf, char *kbuf; /* k-addr because vwrite() takes vmlist_lock rwlock */ int err = 0; + if (!pfn_valid(PFN_DOWN(p))) + return -EIO; + if (p < (unsigned long) high_memory) { unsigned long to_write = min_t(unsigned long, count, (unsigned long)high_memory - p); -- 2.30.2