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authorJann Horn <jannh@google.com>2018-08-28 22:14:20 +0200
committerThomas Gleixner <tglx@linutronix.de>2018-09-03 15:12:09 +0200
commit9da3f2b74054406f87dff7101a569217ffceb29b (patch)
tree12dc39602e4c134a2becbe843925b1e65b6971d8 /mm/maccess.c
parent81fd9c18444ed1199b5a6f6776a395292d4256fb (diff)
downloadlinux-stericsson-9da3f2b74054406f87dff7101a569217ffceb29b.tar.gz
x86/fault: BUG() when uaccess helpers fault on kernel addresses
There have been multiple kernel vulnerabilities that permitted userspace to pass completely unchecked pointers through to userspace accessors: - the waitid() bug - commit 96ca579a1ecc ("waitid(): Add missing access_ok() checks") - the sg/bsg read/write APIs - the infiniband read/write APIs These don't happen all that often, but when they do happen, it is hard to test for them properly; and it is probably also hard to discover them with fuzzing. Even when an unmapped kernel address is supplied to such buggy code, it just returns -EFAULT instead of doing a proper BUG() or at least WARN(). Try to make such misbehaving code a bit more visible by refusing to do a fixup in the pagefault handler code when a userspace accessor causes a #PF on a kernel address and the current context isn't whitelisted. Signed-off-by: Jann Horn <jannh@google.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Tested-by: Kees Cook <keescook@chromium.org> Cc: Andy Lutomirski <luto@kernel.org> Cc: kernel-hardening@lists.openwall.com Cc: dvyukov@google.com Cc: Masami Hiramatsu <mhiramat@kernel.org> Cc: "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com> Cc: Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com> Cc: "David S. Miller" <davem@davemloft.net> Cc: Alexander Viro <viro@zeniv.linux.org.uk> Cc: linux-fsdevel@vger.kernel.org Cc: Borislav Petkov <bp@alien8.de> Link: https://lkml.kernel.org/r/20180828201421.157735-7-jannh@google.com
Diffstat (limited to 'mm/maccess.c')
-rw-r--r--mm/maccess.c6
1 files changed, 6 insertions, 0 deletions
diff --git a/mm/maccess.c b/mm/maccess.c
index ec00be51a24f..f3416632e5a4 100644
--- a/mm/maccess.c
+++ b/mm/maccess.c
@@ -30,8 +30,10 @@ long __probe_kernel_read(void *dst, const void *src, size_t size)
set_fs(KERNEL_DS);
pagefault_disable();
+ current->kernel_uaccess_faults_ok++;
ret = __copy_from_user_inatomic(dst,
(__force const void __user *)src, size);
+ current->kernel_uaccess_faults_ok--;
pagefault_enable();
set_fs(old_fs);
@@ -58,7 +60,9 @@ long __probe_kernel_write(void *dst, const void *src, size_t size)
set_fs(KERNEL_DS);
pagefault_disable();
+ current->kernel_uaccess_faults_ok++;
ret = __copy_to_user_inatomic((__force void __user *)dst, src, size);
+ current->kernel_uaccess_faults_ok--;
pagefault_enable();
set_fs(old_fs);
@@ -94,11 +98,13 @@ long strncpy_from_unsafe(char *dst, const void *unsafe_addr, long count)
set_fs(KERNEL_DS);
pagefault_disable();
+ current->kernel_uaccess_faults_ok++;
do {
ret = __get_user(*dst++, (const char __user __force *)src++);
} while (dst[-1] && ret == 0 && src - unsafe_addr < count);
+ current->kernel_uaccess_faults_ok--;
dst[-1] = '\0';
pagefault_enable();
set_fs(old_fs);