ima: Free IMA measurement buffer after kexec syscall

IMA allocates kernel virtual memory to carry forward the measurement
list, from the current kernel to the next kernel on kexec system call,
in ima_add_kexec_buffer() function.  This buffer is not freed before
completing the kexec system call resulting in memory leak.

Add ima_buffer field in "struct kimage" to store the virtual address
of the buffer allocated for the IMA measurement list.
Free the memory allocated for the IMA measurement list in
kimage_file_post_load_cleanup() function.

Signed-off-by: Lakshmi Ramasubramanian <nramas@linux.microsoft.com>
Suggested-by: Tyler Hicks <tyhicks@linux.microsoft.com>
Reviewed-by: Thiago Jung Bauermann <bauerman@linux.ibm.com>
Reviewed-by: Tyler Hicks <tyhicks@linux.microsoft.com>
Fixes: 7b8589cc29 ("ima: on soft reboot, save the measurement list")
Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>

include/linux/kexec.h

@@ -300,6 +300,11 @@ struct kimage {
 	/* Information for loading purgatory */
 	struct purgatory_info purgatory_info;
 #endif
+
+#ifdef CONFIG_IMA_KEXEC
+	/* Virtual address of IMA measurement buffer for kexec syscall */
+	void *ima_buffer;
+#endif
 };
 
 /* kexec interface functions */

kernel/kexec_file.c

@@ -166,6 +166,11 @@ void kimage_file_post_load_cleanup(struct kimage *image)
 	vfree(pi->sechdrs);
 	pi->sechdrs = NULL;
 
+#ifdef CONFIG_IMA_KEXEC
+	vfree(image->ima_buffer);
+	image->ima_buffer = NULL;
+#endif /* CONFIG_IMA_KEXEC */
+
 	/* See if architecture has anything to cleanup post load */
 	arch_kimage_file_post_load_cleanup(image);
 

security/integrity/ima/ima_kexec.c

@@ -129,6 +129,8 @@ void ima_add_kexec_buffer(struct kimage *image)
 		return;
 	}
 
+	image->ima_buffer = kexec_buffer;
+
 	pr_debug("kexec measurement buffer for the loaded kernel at 0x%lx.\n",
 		 kbuf.mem);
 }