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daemon/mkfs: disable creation of fake MBR partition table with "mkfs.fat"

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Search the usage output of "mkfs.fat" for "--mbr[="; cache the result for
further invocations. If the option is supported, pass "--mbr=n" to
"mkfs.fat". This will prevent the creation of a bogus partition table
whose first (and only) entry describes a partition that contains the
partition table.

(Such a bogus partition table breaks "parted", which is a tool used by
libguestfs extensively, both internally and in public libguestfs APIs.)

Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=1931821
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Acked-by: Richard W.M. Jones <rjones@redhat.com>
Message-Id: <20211125094954.9713-2-lersek@redhat.com>
This commit is contained in:
Laszlo Ersek
2021-11-25 10:49:50 +01:00
committed by Richard W.M. Jones
parent 07049b2a1f
commit e8e2f417c9
1 changed files with 27 additions and 0 deletions
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27
daemon/mkfs.c
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@@ -30,6 +30,14 @@
#define MAX_ARGS 64
enum fat_mbr_option {
FMO_UNCHECKED,
FMO_DOESNT_EXIST,
FMO_EXISTS,
};
static enum fat_mbr_option fat_mbr_option = FMO_UNCHECKED;
/* Takes optional arguments, consult optargs_bitmask. */
int
do_mkfs (const char *fstype, const char *device, int blocksize,
@@ -101,6 +109,25 @@ do_mkfs (const char *fstype, const char *device, int blocksize,
STREQ (fstype, "msdos"))
ADD_ARG (argv, i, "-I");
/* Prevent mkfs.fat from creating a bogus partition table (RHBZ#1931821). */
if (STREQ (fstype, "fat") || STREQ (fstype, "vfat") ||
STREQ (fstype, "msdos")) {
if (fat_mbr_option == FMO_UNCHECKED) {
CLEANUP_FREE char *usage_err = NULL;
fat_mbr_option = FMO_DOESNT_EXIST;
/* Invoking either version 3 of version 4 of mkfs.fat without any options
* will make it (a) print a usage summary to stderr, (b) exit with status
* 1.
*/
r = commandr (NULL, &usage_err, "mkfs.fat", (char *)NULL);
if (r == 1 && strstr (usage_err, "--mbr[=") != NULL)
fat_mbr_option = FMO_EXISTS;
}
if (fat_mbr_option == FMO_EXISTS)
ADD_ARG (argv, i, "--mbr=n");
}
/* Process blocksize parameter if set. */
if (optargs_bitmask & GUESTFS_MKFS_BLOCKSIZE_BITMASK) {
if (blocksize <= 0 || !is_power_of_2 (blocksize)) {