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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 /fs
parent81fd9c18444ed1199b5a6f6776a395292d4256fb (diff)
downloadlinux-9da3f2b74054406f87dff7101a569217ffceb29b.tar.bz2
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 'fs')
-rw-r--r--fs/namespace.c2
1 files changed, 2 insertions, 0 deletions
diff --git a/fs/namespace.c b/fs/namespace.c
index 99186556f8d3..d86830c86ce8 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -2642,6 +2642,7 @@ static long exact_copy_from_user(void *to, const void __user * from,
if (!access_ok(VERIFY_READ, from, n))
return n;
+ current->kernel_uaccess_faults_ok++;
while (n) {
if (__get_user(c, f)) {
memset(t, 0, n);
@@ -2651,6 +2652,7 @@ static long exact_copy_from_user(void *to, const void __user * from,
f++;
n--;
}
+ current->kernel_uaccess_faults_ok--;
return n;
}