From: B Horn <b...@horn.uk>
It was possible to delete a loopback while there were still references
to it. This led to an exploitable use-after-free.
Fixed by implementing a reference counting in the grub_loopback struct.
Reported-by: B Horn <b...@horn.uk>
Signed-off-by: B Horn <b...@horn.uk>
Reviewed-by: Daniel Kiper <daniel.ki...@oracle.com>
---
grub-core/disk/loopback.c | 18 ++++++++++++++++++
include/grub/err.h | 3 ++-
2 files changed, 20 insertions(+), 1 deletion(-)
diff --git a/grub-core/disk/loopback.c b/grub-core/disk/loopback.c
index 4635dcfde..2bea4e922 100644
--- a/grub-core/disk/loopback.c
+++ b/grub-core/disk/loopback.c
@@ -24,6 +24,7 @@
#include <grub/mm.h>
#include <grub/extcmd.h>
#include <grub/i18n.h>
+#include <grub/safemath.h>
GRUB_MOD_LICENSE ("GPLv3+");
@@ -33,6 +34,7 @@ struct grub_loopback
grub_file_t file;
struct grub_loopback *next;
unsigned long id;
+ grub_uint64_t refcnt;
};
static struct grub_loopback *loopback_list;
@@ -64,6 +66,8 @@ delete_loopback (const char *name)
if (! dev)
return grub_error (GRUB_ERR_BAD_DEVICE, "device not found");
+ if (dev->refcnt > 0)
+ return grub_error (GRUB_ERR_STILL_REFERENCED, "device still referenced");
/* Remove the device from the list. */
*prev = dev->next;
@@ -120,6 +124,7 @@ grub_cmd_loopback (grub_extcmd_context_t ctxt, int argc,
char **args)
newdev->file = file;
newdev->id = last_id++;
+ newdev->refcnt = 0;
/* Add the new entry to the list. */
newdev->next = loopback_list;
@@ -161,6 +166,9 @@ grub_loopback_open (const char *name, grub_disk_t disk)
if (! dev)
return grub_error (GRUB_ERR_UNKNOWN_DEVICE, "can't open device");
+ if (grub_add (dev->refcnt, 1, &dev->refcnt))
+ grub_fatal ("Reference count overflow");
+
/* Use the filesize for the disk size, round up to a complete sector. */
if (dev->file->size != GRUB_FILE_SIZE_UNKNOWN)
disk->total_sectors = ((dev->file->size + GRUB_DISK_SECTOR_SIZE - 1)
@@ -178,6 +186,15 @@ grub_loopback_open (const char *name, grub_disk_t disk)
return 0;
}
+static void
+grub_loopback_close (grub_disk_t disk)
+{
+ struct grub_loopback *dev = disk->data;
+
+ if (grub_sub (dev->refcnt, 1, &dev->refcnt))
+ grub_fatal ("Reference count underflow");
+}
+
static grub_err_t
grub_loopback_read (grub_disk_t disk, grub_disk_addr_t sector,
grub_size_t size, char *buf)
@@ -220,6 +237,7 @@ static struct grub_disk_dev grub_loopback_dev =
.id = GRUB_DISK_DEVICE_LOOPBACK_ID,
.disk_iterate = grub_loopback_iterate,
.disk_open = grub_loopback_open,
+ .disk_close = grub_loopback_close,
.disk_read = grub_loopback_read,
.disk_write = grub_loopback_write,
.next = 0
diff --git a/include/grub/err.h b/include/grub/err.h
index 1c07034cd..b0e54e0a0 100644
--- a/include/grub/err.h
+++ b/include/grub/err.h
@@ -73,7 +73,8 @@ typedef enum
GRUB_ERR_NET_NO_DOMAIN,
GRUB_ERR_EOF,
GRUB_ERR_BAD_SIGNATURE,
- GRUB_ERR_BAD_FIRMWARE
+ GRUB_ERR_BAD_FIRMWARE,
+ GRUB_ERR_STILL_REFERENCED
}
grub_err_t;
--
2.11.0
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