Fix: handle integer capture page faults as skip field

Now that we have the appropriate save/restore position mechanism for
error handling in place, we can handle page faults on integer
copy-from-user by skipping the offending captured field entirely rather
than relying on an arbitrary 0 value.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Change-Id: I4ec6243d96753ce7e9c6230563713aeacb126567

diff --git a/src/lttng-event-notifier-notification.c b/src/lttng-event-notifier-notification.c
index a4e945673633a4cc7c761a73aa388b5678c74106..7d345acc8be648f7ab3719fbaed7a63b09b908cd 100644 (file)
--- a/src/lttng-event-notifier-notification.c
+++ b/src/lttng-event-notifier-notification.c
@@ -81,6 +81,8 @@ int capture_enum(struct lttng_msgpack_writer *writer,
                break;
        default:
                WARN_ON_ONCE(1);
+               ret = -1;
+               goto end;
        }
 
        ret = lttng_msgpack_end_map(writer);
@@ -89,8 +91,9 @@ end:
 }
 
 static
-int64_t capture_sequence_element_signed(uint8_t *ptr,
-               const struct lttng_kernel_type_integer *type)
+int capture_sequence_element_signed(uint8_t *ptr,
+               const struct lttng_kernel_type_integer *type,
+               int64_t *_value)
 {
        int64_t value = 0;
        unsigned int size = type->size;
@@ -104,7 +107,7 @@ int64_t capture_sequence_element_signed(uint8_t *ptr,
 
                if (user) {
                        if (lttng_copy_from_user_check_nofault(&tmp, ptr, sizeof(int8_t)))
-                               tmp = 0;
+                               return -1;
                } else {
                        tmp = *ptr;
                }
@@ -117,7 +120,7 @@ int64_t capture_sequence_element_signed(uint8_t *ptr,
 
                if (user) {
                        if (lttng_copy_from_user_check_nofault(&tmp, ptr, sizeof(int16_t)))
-                               tmp = 0;
+                               return -1;
                } else {
                        tmp = *(int16_t *) ptr;
                }
@@ -132,7 +135,7 @@ int64_t capture_sequence_element_signed(uint8_t *ptr,
 
                if (user) {
                        if (lttng_copy_from_user_check_nofault(&tmp, ptr, sizeof(int32_t)))
-                               tmp = 0;
+                               return -1;
                } else {
                        tmp = *(int32_t *) ptr;
                }
@@ -147,7 +150,7 @@ int64_t capture_sequence_element_signed(uint8_t *ptr,
 
                if (user) {
                        if (lttng_copy_from_user_check_nofault(&tmp, ptr, sizeof(int64_t)))
-                               tmp = 0;
+                               return -1;
                } else {
                        tmp = *(int64_t *) ptr;
                }
@@ -158,14 +161,17 @@ int64_t capture_sequence_element_signed(uint8_t *ptr,
        }
        default:
                WARN_ON_ONCE(1);
+               return -1;
        }
 
-       return value;
+       *_value = value;
+       return 0;
 }
 
 static
-uint64_t capture_sequence_element_unsigned(uint8_t *ptr,
-               const struct lttng_kernel_type_integer *type)
+int capture_sequence_element_unsigned(uint8_t *ptr,
+               const struct lttng_kernel_type_integer *type,
+               uint64_t *_value)
 {
        uint64_t value = 0;
        unsigned int size = type->size;
@@ -179,7 +185,7 @@ uint64_t capture_sequence_element_unsigned(uint8_t *ptr,
 
                if (user) {
                        if (lttng_copy_from_user_check_nofault(&tmp, ptr, sizeof(uint8_t)))
-                               tmp = 0;
+                               return -1;
                } else {
                        tmp = *ptr;
                }
@@ -192,7 +198,7 @@ uint64_t capture_sequence_element_unsigned(uint8_t *ptr,
 
                if (user) {
                        if (lttng_copy_from_user_check_nofault(&tmp, ptr, sizeof(uint16_t)))
-                               tmp = 0;
+                               return -1;
                } else {
                        tmp = *(uint16_t *) ptr;
                }
@@ -207,7 +213,7 @@ uint64_t capture_sequence_element_unsigned(uint8_t *ptr,
 
                if (user) {
                        if (lttng_copy_from_user_check_nofault(&tmp, ptr, sizeof(uint32_t)))
-                               tmp = 0;
+                               return -1;
                } else {
                        tmp = *(uint32_t *) ptr;
                }
@@ -222,7 +228,7 @@ uint64_t capture_sequence_element_unsigned(uint8_t *ptr,
 
                if (user) {
                        if (lttng_copy_from_user_check_nofault(&tmp, ptr, sizeof(uint64_t)))
-                               tmp = 0;
+                               return -1;
                } else {
                        tmp = *(uint64_t *) ptr;
                }
@@ -233,9 +239,11 @@ uint64_t capture_sequence_element_unsigned(uint8_t *ptr,
        }
        default:
                WARN_ON_ONCE(1);
+               return -1;
        }
 
-       return value;
+       *_value = value;
+       return 0;
 }
 
 int capture_sequence(struct lttng_msgpack_writer *writer,
@@ -271,14 +279,24 @@ int capture_sequence(struct lttng_msgpack_writer *writer,
        signedness = integer_type->signedness;
        for (i = 0; i < output->u.sequence.nr_elem; i++) {
                if (signedness) {
-                       ret = lttng_msgpack_write_signed_integer(writer,
-                               capture_sequence_element_signed(ptr, integer_type));
+                       int64_t v;
+
+                       ret = capture_sequence_element_signed(ptr, integer_type, &v);
+                       if (ret) {
+                               goto end;
+                       }
+                       ret = lttng_msgpack_write_signed_integer(writer, v);
                        if (ret) {
                                goto end;
                        }
                } else {
-                       ret = lttng_msgpack_write_unsigned_integer(writer,
-                               capture_sequence_element_unsigned(ptr, integer_type));
+                       uint64_t v;
+
+                       ret = capture_sequence_element_unsigned(ptr, integer_type, &v);
+                       if (ret) {
+                               goto end;
+                       }
+                       ret = lttng_msgpack_write_unsigned_integer(writer, v);
                        if (ret) {
                                goto end;
                        }