Messages in this thread Patch in this message | | | From | Robin Murphy <> | Subject | [PATCH v2] drivers: char: mem: Check {read,write}_kmem() addresses | Date | Wed, 1 Jun 2016 19:21:42 +0100 |
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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 <wangkefeng.wang@huawei.com> Signed-off-by: Robin Murphy <robin.murphy@arm.com> ---
v2: Make the error code consistent and more appropriate, tweak commit message.
drivers/char/mem.c | 6 ++++++ 1 file changed, 6 insertions(+)
diff --git a/drivers/char/mem.c b/drivers/char/mem.c index 71025c2f6bbb..e1b8d960341f 100644 --- a/drivers/char/mem.c +++ b/drivers/char/mem.c @@ -384,6 +384,9 @@ 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; @@ -512,6 +515,9 @@ 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); -- 2.8.1.dirty
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