fix: don't allow userspace copy to read kernel memory

[lttng-modules.git] / lttng-filter-interpreter.c

diff --git a/lttng-filter-interpreter.c b/lttng-filter-interpreter.c
index 3dad6cc6650830f2990ec410f09b523dd59573d3..21169f01fe3ef22fc0f996246d898564366676b8 100644 (file)
--- a/lttng-filter-interpreter.c
+++ b/lttng-filter-interpreter.c
@@ -81,16 +81,14 @@ static
 int stack_star_glob_match(struct estack *stack, int top, const char *cmp_type)
 {
        bool has_user = false;
-       mm_segment_t old_fs;
        int result;
        struct estack_entry *pattern_reg;
        struct estack_entry *candidate_reg;
 
+       /* Disable the page fault handler when reading from userspace. */
        if (estack_bx(stack, top)->u.s.user
                        || estack_ax(stack, top)->u.s.user) {
                has_user = true;
-               old_fs = get_fs();
-               set_fs(KERNEL_DS);
                pagefault_disable();
        }
 
@@ -106,10 +104,8 @@ int stack_star_glob_match(struct estack *stack, int top, const char *cmp_type)
        /* Perform the match operation. */
        result = !strutils_star_glob_match_char_cb(get_char_at_cb,
                pattern_reg, get_char_at_cb, candidate_reg);
-       if (has_user) {
+       if (has_user)
                pagefault_enable();
-               set_fs(old_fs);
-       }
 
        return result;
 }
@@ -119,13 +115,10 @@ int stack_strcmp(struct estack *stack, int top, const char *cmp_type)
 {
        size_t offset_bx = 0, offset_ax = 0;
        int diff, has_user = 0;
-       mm_segment_t old_fs;
 
        if (estack_bx(stack, top)->u.s.user
                        || estack_ax(stack, top)->u.s.user) {
                has_user = 1;
-               old_fs = get_fs();
-               set_fs(KERNEL_DS);
                pagefault_disable();
        }
 
@@ -210,10 +203,9 @@ int stack_strcmp(struct estack *stack, int top, const char *cmp_type)
                offset_bx++;
                offset_ax++;
        }
-       if (has_user) {
+       if (has_user)
                pagefault_enable();
-               set_fs(old_fs);
-       }
+
        return diff;
 }