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grub-editenv: Make grub-editenv chase symlinks including those across devices

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The grub-editenv create command will wrongly overwrite /boot/grub2/grubenv
with a regular file if grubenv is a symbolic link. But instead, it should
create a new file in the path the symlink points to.

This lets /boot/grub2/grubenv be a symlink to /boot/efi/EFI/fedora/grubenv
even when they're different mount points, which allows grub2-editenv to be
the same across platforms (i.e. UEFI vs BIOS).

For example, in Fedora the GRUB EFI builds have prefix set to /EFI/fedora
(on the EFI System Partition), but for BIOS machine it'll be /boot/grub2
(which may or may not be its own mountpoint).

With this patch, on EFI machines we can make /boot/grub2/grubenv a symlink
to /boot/efi/EFI/fedora/grubenv, and the same copy of grub-set-default will
work on both kinds of systems.

Windows doesn't implement a readlink primitive, so the current behaviour is
maintained for this operating system.

Signed-off-by: Peter Jones <pjones@redhat.com>
Signed-off-by: Jonathan Lebon <jlebon@redhat.com>
Reviewed-by: Adam Jackson <ajax@redhat.com>
Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
This commit is contained in:
Peter Jones 2020-01-17 17:10:43 +01:00 committed by Daniel Kiper
parent 03e72830ab
commit 0ad07e928a
2 changed files with 76 additions and 0 deletions
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11
Makefile.util.def
View file

@ -242,8 +242,19 @@ program = {
common = util/grub-editenv.c;
common = util/editenv.c;
common = util/grub-install-common.c;
common = grub-core/osdep/init.c;
common = grub-core/osdep/compress.c;
extra_dist = grub-core/osdep/unix/compress.c;
extra_dist = grub-core/osdep/basic/compress.c;
common = util/mkimage.c;
common = util/grub-mkimage32.c;
common = util/grub-mkimage64.c;
common = grub-core/osdep/config.c;
common = util/config.c;
common = util/resolve.c;
ldadd = '$(LIBLZMA)';
ldadd = libgrubmods.a;
ldadd = libgrubgcry.a;
ldadd = libgrubkern.a;

65
util/editenv.c
View file

@ -28,6 +28,9 @@
#include <errno.h>
#include <string.h>
#if !defined(_WIN32)
#include <libgen.h>
#endif
#define DEFAULT_ENVBLK_SIZE 1024
#define GRUB_ENVBLK_MESSAGE "# WARNING: Do not edit this file by tools other than "PACKAGE"-editenv!!!\n"
@ -37,6 +40,11 @@ grub_util_create_envblk_file (const char *name)
{
FILE *fp;
char *buf, *pbuf, *namenew;
#if !defined(_WIN32)
ssize_t size = 1;
char *rename_target = xstrdup (name);
int rc;
#endif
buf = xmalloc (DEFAULT_ENVBLK_SIZE);
@ -64,7 +72,64 @@ grub_util_create_envblk_file (const char *name)
free (buf);
fclose (fp);
#if defined(_WIN32)
if (grub_util_rename (namenew, name) < 0)
grub_util_error (_("cannot rename the file %s to %s"), namenew, name);
#else
while (1)
{
char *linkbuf;
ssize_t retsize;
linkbuf = xmalloc (size + 1);
retsize = grub_util_readlink (rename_target, linkbuf, size);
if (retsize < 0 && (errno == ENOENT || errno == EINVAL))
{
free (linkbuf);
break;
}
else if (retsize < 0)
{
free (linkbuf);
grub_util_error (_("cannot rename the file %s to %s: %m"), namenew, name);
}
else if (retsize == size)
{
free (linkbuf);
size += 128;
continue;
}
linkbuf[retsize] = '\0';
if (linkbuf[0] == '/')
{
free (rename_target);
rename_target = linkbuf;
}
else
{
char *dbuf = xstrdup (rename_target);
const char *dir = dirname (dbuf);
free (rename_target);
rename_target = xasprintf ("%s/%s", dir, linkbuf);
free (dbuf);
free (linkbuf);
}
}
rc = grub_util_rename (namenew, rename_target);
if (rc < 0 && errno == EXDEV)
{
rc = grub_install_copy_file (namenew, rename_target, 1);
grub_util_unlink (namenew);
}
free (rename_target);
if (rc < 0)
grub_util_error (_("cannot rename the file %s to %s: %m"), namenew, name);
#endif
free (namenew);
}