[PATCH lttng-tools 1/2] Fix: syscall_table_nb_entry invalid value when no syscalls TPs are defined

[Jonathan Rajotte <jonathan.rajotte-julien@efficios.com>]

fscanf on an empty file returns directly without assigning value to
'index' leading to assigning the value of an uninitialized variable to
syscall_table_nb_entry. This can result in memory allocation problems
when listing syscalls on 'lttng list --kernel --syscall'[1][2].

Fixes #1091

[1] https://bugs.lttng.org/issues/1091
[2] https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1671063/

Signed-off-by: Jonathan Rajotte <jonathan.rajotte-julien@efficios.com>
---
 src/bin/lttng-sessiond/syscall.c | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/src/bin/lttng-sessiond/syscall.c b/src/bin/lttng-sessiond/syscall.c
index 6ee38bd..c21e4d8 100644
--- a/src/bin/lttng-sessiond/syscall.c
+++ b/src/bin/lttng-sessiond/syscall.c
@@ -16,6 +16,8 @@
  */
 
 #define _LGPL_SOURCE
+#include <stdbool.h>
+
 #include <common/bitfield.h>
 #include <common/common.h>
 #include <common/kernel-ctl/kernel-ctl.h>
@@ -43,7 +45,8 @@ int syscall_init_table(void)
 	size_t nbmem;
 	FILE *fp;
 	/* Syscall data from the kernel. */
-	size_t index;
+	size_t index = 0;
+	bool at_least_one_syscall = false;
 	uint32_t bitness;
 	char name[SYSCALL_NAME_LEN];
 
@@ -76,7 +79,8 @@ int syscall_init_table(void)
 				name = %" XSTR(SYSCALL_NAME_LEN) "[^;]; \
 				bitness = %u; };\n",
 				&index, name, &bitness) == 3) {
-		if (index >= nbmem ) {
+		at_least_one_syscall = true;
+		if (index >= nbmem) {
 			struct syscall *new_list;
 			size_t new_nbmem;
 
@@ -123,7 +127,10 @@ int syscall_init_table(void)
 		*/
 	}
 
-	syscall_table_nb_entry = index;
+	/* Index start at 0. */
+	if (at_least_one_syscall) {
+		syscall_table_nb_entry = index + 1;
+	}
 
 	ret = 0;
 
-- 
2.7.4

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