coredump: show supported coredump modes

Allow userspace to discover what coredump modes are supported.

Link: https://lore.kernel.org/[email protected]
Acked-by: Luca Boccassi <[email protected]>
Reviewed-by: Jann Horn <[email protected]>
Reviewed-by: Alexander Mikhalitsyn <[email protected]>
Signed-off-by: Christian Brauner <[email protected]>

Author: brauner

fs/coredump.c

@@ -1248,6 +1248,12 @@ static int proc_dostring_coredump(const struct ctl_table *table, int write,
 
 static const unsigned int core_file_note_size_min = CORE_FILE_NOTE_SIZE_DEFAULT;
 static const unsigned int core_file_note_size_max = CORE_FILE_NOTE_SIZE_MAX;
+static char core_modes[] = {
+	"file\npipe"
+#ifdef CONFIG_UNIX
+	"\nsocket"
+#endif
+};
 
 static const struct ctl_table coredump_sysctls[] = {
 	{
@@ -1291,6 +1297,13 @@ static const struct ctl_table coredump_sysctls[] = {
 		.extra1		= SYSCTL_ZERO,
 		.extra2		= SYSCTL_ONE,
 	},
+	{
+		.procname	= "core_modes",
+		.data		= core_modes,
+		.maxlen		= sizeof(core_modes) - 1,
+		.mode		= 0444,
+		.proc_handler	= proc_dostring,
+	},
 };
 
 static int __init init_fs_coredump_sysctls(void)