109 lines
3.4 KiB
Diff
109 lines
3.4 KiB
Diff
From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
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From: B Horn <b@horn.uk>
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Date: Tue, 11 Feb 2025 15:22:28 -0600
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Subject: [PATCH] disk/loopback: Reference tracking for the loopback
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It was possible to delete a loopback while there were still references
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to it. This led to an exploitable use-after-free.
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Fixed by implementing a reference counting in the grub_loopback struct.
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Reported-by: B Horn <b@horn.uk>
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Signed-off-by: B Horn <b@horn.uk>
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Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
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---
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grub-core/disk/loopback.c | 17 +++++++++++++++++
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include/grub/err.h | 3 ++-
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include/grub/loopback.h | 1 +
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3 files changed, 20 insertions(+), 1 deletion(-)
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diff --git a/grub-core/disk/loopback.c b/grub-core/disk/loopback.c
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index 11a5e0cbd..f39281323 100644
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--- a/grub-core/disk/loopback.c
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+++ b/grub-core/disk/loopback.c
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@@ -25,6 +25,7 @@
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#include <grub/mm.h>
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#include <grub/extcmd.h>
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#include <grub/i18n.h>
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+#include <grub/safemath.h>
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GRUB_MOD_LICENSE ("GPLv3+");
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@@ -57,6 +58,8 @@ delete_loopback (const char *name)
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if (! dev)
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return grub_error (GRUB_ERR_BAD_DEVICE, "device not found");
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+ if (dev->refcnt > 0)
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+ return grub_error (GRUB_ERR_STILL_REFERENCED, "device still referenced");
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/* Remove the device from the list. */
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*prev = dev->next;
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@@ -113,6 +116,7 @@ grub_cmd_loopback (grub_extcmd_context_t ctxt, int argc, char **args)
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newdev->file = file;
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newdev->id = last_id++;
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+ newdev->refcnt = 0;
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/* Add the new entry to the list. */
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newdev->next = loopback_list;
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@@ -154,6 +158,9 @@ grub_loopback_open (const char *name, grub_disk_t disk)
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if (! dev)
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return grub_error (GRUB_ERR_UNKNOWN_DEVICE, "can't open device");
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+ if (grub_add (dev->refcnt, 1, &dev->refcnt))
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+ grub_fatal ("Reference count overflow");
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+
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/* Use the filesize for the disk size, round up to a complete sector. */
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if (dev->file->size != GRUB_FILE_SIZE_UNKNOWN)
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disk->total_sectors = ((dev->file->size + GRUB_DISK_SECTOR_SIZE - 1)
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@@ -171,6 +178,15 @@ grub_loopback_open (const char *name, grub_disk_t disk)
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return 0;
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}
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+static void
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+grub_loopback_close (grub_disk_t disk)
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+{
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+ struct grub_loopback *dev = disk->data;
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+
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+ if (grub_sub (dev->refcnt, 1, &dev->refcnt))
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+ grub_fatal ("Reference count underflow");
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+}
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+
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static grub_err_t
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grub_loopback_read (grub_disk_t disk, grub_disk_addr_t sector,
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grub_size_t size, char *buf)
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@@ -213,6 +229,7 @@ static struct grub_disk_dev grub_loopback_dev =
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.id = GRUB_DISK_DEVICE_LOOPBACK_ID,
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.disk_iterate = grub_loopback_iterate,
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.disk_open = grub_loopback_open,
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+ .disk_close = grub_loopback_close,
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.disk_read = grub_loopback_read,
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.disk_write = grub_loopback_write,
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.next = 0
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diff --git a/include/grub/err.h b/include/grub/err.h
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index 3c587b9b8..29f1a73c5 100644
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--- a/include/grub/err.h
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+++ b/include/grub/err.h
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@@ -73,7 +73,8 @@ typedef enum
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GRUB_ERR_NET_NO_DOMAIN,
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GRUB_ERR_EOF,
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GRUB_ERR_BAD_SIGNATURE,
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- GRUB_ERR_BAD_FIRMWARE
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+ GRUB_ERR_BAD_FIRMWARE,
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+ GRUB_ERR_STILL_REFERENCED
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}
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grub_err_t;
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diff --git a/include/grub/loopback.h b/include/grub/loopback.h
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index 3b9a9e32e..915ef65fc 100644
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--- a/include/grub/loopback.h
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+++ b/include/grub/loopback.h
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@@ -25,6 +25,7 @@ struct grub_loopback
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grub_file_t file;
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struct grub_loopback *next;
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unsigned long id;
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+ grub_uint64_t refcnt;
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};
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#endif /* ! GRUB_LOOPBACK_HEADER */
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