From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001 From: B Horn Date: Sun, 12 May 2024 03:26:19 +0100 Subject: [PATCH] disk/loopback: Reference tracking for the loopback 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 Signed-off-by: B Horn Reviewed-by: Daniel Kiper --- 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 9406d931c..e7052a9cb 100644 --- a/grub-core/disk/loopback.c +++ b/grub-core/disk/loopback.c @@ -24,6 +24,7 @@ #include #include #include +#include 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; @@ -63,6 +65,8 @@ 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; @@ -124,6 +128,7 @@ 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; @@ -165,6 +170,9 @@ 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) @@ -182,6 +190,15 @@ 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) @@ -224,6 +241,7 @@ static struct grub_disk_dev grub_loopback_dev = .id = GRUB_DISK_DEVICE_LOOPBACK_ID, .iterate = grub_loopback_iterate, .open = grub_loopback_open, + .close = grub_loopback_close, .read = grub_loopback_read, .write = grub_loopback_write, .next = 0 diff --git a/include/grub/err.h b/include/grub/err.h index 9b830757d..1b5335610 100644 --- a/include/grub/err.h +++ b/include/grub/err.h @@ -71,7 +71,8 @@ typedef enum GRUB_ERR_NET_PACKET_TOO_BIG, GRUB_ERR_NET_NO_DOMAIN, GRUB_ERR_EOF, - GRUB_ERR_BAD_SIGNATURE + GRUB_ERR_BAD_SIGNATURE, + GRUB_ERR_STILL_REFERENCED } grub_err_t;