bpf: Restrict bpf when kernel lockdown is in confidentiality mode
authorDavid Howells <dhowells@redhat.com>
Tue, 20 Aug 2019 00:17:59 +0000 (17:17 -0700)
committerJames Morris <jmorris@namei.org>
Tue, 20 Aug 2019 04:54:16 +0000 (21:54 -0700)
bpf_read() and bpf_read_str() could potentially be abused to (eg) allow
private keys in kernel memory to be leaked. Disable them if the kernel
has been locked down in confidentiality mode.

Suggested-by: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Signed-off-by: Matthew Garrett <mjg59@google.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
cc: netdev@vger.kernel.org
cc: Chun-Yi Lee <jlee@suse.com>
cc: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: James Morris <jmorris@namei.org>
include/linux/security.h
kernel/trace/bpf_trace.c
security/lockdown/lockdown.c

index 0b2529dbf0f4a05010c9c34956f682af8ae59e93..e604f4c67f03e87c9dfb9a9bbe943b3965af831c 100644 (file)
@@ -118,6 +118,7 @@ enum lockdown_reason {
        LOCKDOWN_INTEGRITY_MAX,
        LOCKDOWN_KCORE,
        LOCKDOWN_KPROBES,
+       LOCKDOWN_BPF_READ,
        LOCKDOWN_CONFIDENTIALITY_MAX,
 };
 
index 1c9a4745e596d91bde5fc5910fc4f8bcb318529e..33a954c367f3501e78b85a5723271892a92d0e8f 100644 (file)
@@ -139,8 +139,13 @@ BPF_CALL_3(bpf_probe_read, void *, dst, u32, size, const void *, unsafe_ptr)
 {
        int ret;
 
+       ret = security_locked_down(LOCKDOWN_BPF_READ);
+       if (ret < 0)
+               goto out;
+
        ret = probe_kernel_read(dst, unsafe_ptr, size);
        if (unlikely(ret < 0))
+out:
                memset(dst, 0, size);
 
        return ret;
@@ -566,6 +571,10 @@ BPF_CALL_3(bpf_probe_read_str, void *, dst, u32, size,
 {
        int ret;
 
+       ret = security_locked_down(LOCKDOWN_BPF_READ);
+       if (ret < 0)
+               goto out;
+
        /*
         * The strncpy_from_unsafe() call will likely not fill the entire
         * buffer, but that's okay in this circumstance as we're probing
@@ -577,6 +586,7 @@ BPF_CALL_3(bpf_probe_read_str, void *, dst, u32, size,
         */
        ret = strncpy_from_unsafe(dst, unsafe_ptr, size);
        if (unlikely(ret < 0))
+out:
                memset(dst, 0, size);
 
        return ret;
index 27b2cf51e443c3536050910766ca81bc411bf173..2397772c56bdb82c24a51b63158c0236ad7011a6 100644 (file)
@@ -33,6 +33,7 @@ static char *lockdown_reasons[LOCKDOWN_CONFIDENTIALITY_MAX+1] = {
        [LOCKDOWN_INTEGRITY_MAX] = "integrity",
        [LOCKDOWN_KCORE] = "/proc/kcore access",
        [LOCKDOWN_KPROBES] = "use of kprobes",
+       [LOCKDOWN_BPF_READ] = "use of bpf to read kernel RAM",
        [LOCKDOWN_CONFIDENTIALITY_MAX] = "confidentiality",
 };