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ostree-prepare-root: Fix running with musl 

musl libc's implementation of `realpath` works by opening the path and then
doing a lookup in `/proc/self/fd` to find the canonical path.  This fails
if `/proc` is not mounted.  This causes problems for us if
`ostree-prepare-root` is `init` as `/proc` won't be mounted.

We have to mount `/proc` anyway for `/proc/cmdline` so this fix just
expands the scope over which `/proc` is mounted to include both our
`realpath` calls.

See also:

* http://www.openwall.com/lists/musl/2016/06/08/2 and
* http://git.musl-libc.org/cgit/musl/tree/src/misc/realpath.c?id=e738b8cbe64b6dd3ed9f47b6d4cd7eb2c422b38d

Closes: #485
Approved by: cgwalters
This commit is contained in:
William Manley 2016-08-31 17:15:48 +01:00 committed by Atomic Bot
parent 5424404813
commit 2aacc6912b
2 changed files with 28 additions and 18 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

35
src/switchroot/ostree-prepare-root.c
View File

@ -80,26 +80,10 @@ parse_ostree_cmdline (void)
char *cmdline = NULL;
const char *iter;
char *ret = NULL;
int tmp_errno;
cmdline = read_proc_cmdline ();
if (!cmdline)
{
// Mount proc
if (mount ("proc", "/proc", "proc", 0, NULL) < 0)
err (EXIT_FAILURE, "failed to mount proc on /proc");
cmdline = read_proc_cmdline ();
tmp_errno = errno;
/* Leave the filesystem in the state that we found it: */
if (umount ("/proc"))
err (EXIT_FAILURE, "failed to umount proc from /proc");
errno = tmp_errno;
if (!cmdline)
err (EXIT_FAILURE, "failed to read /proc/cmdline");
}
iter = cmdline;
while (iter != NULL)
@ -178,17 +162,36 @@ main(int argc, char *argv[])
char *deploy_path = NULL;
char srcpath[PATH_MAX];
struct stat stbuf;
int we_mounted_proc = 0;
if (argc < 2)
root_arg = "/";
else
root_arg = argv[1];
if (stat ("/proc/cmdline", &stbuf) < 0)
{
if (errno != ENOENT)
err (EXIT_FAILURE, "stat(\"/proc/cmdline\") failed");
/* We need /proc mounted for /proc/cmdline and realpath (on musl) to
* work: */
if (mount ("proc", "/proc", "proc", 0, NULL) < 0)
err (EXIT_FAILURE, "failed to mount proc on /proc");
we_mounted_proc = 1;
}
root_mountpoint = realpath (root_arg, NULL);
if (root_mountpoint == NULL)
err (EXIT_FAILURE, "realpath(\"%s\")", root_arg);
deploy_path = resolve_deploy_path (root_mountpoint);
if (we_mounted_proc)
{
/* Leave the filesystem in the state that we found it: */
if (umount ("/proc"))
err (EXIT_FAILURE, "failed to umount proc from /proc");
}
/* Work-around for a kernel bug: for some reason the kernel
* refuses switching root if any file systems are mounted
* MS_SHARED. Hence remount them MS_PRIVATE here as a

9
tests/test-switchroot.sh
View File

@ -4,7 +4,14 @@ this_script="${BASH_SOURCE:-$(readlink -f "$0")}"
setup_bootfs() {
mkdir -p "$1/proc" "$1/bin"
echo "quiet ostree=/ostree/boot.0 ro" >"$1/proc/cmdline"
# We need the real /proc mounted here so musl's realpath will work, but we
# want to be able to override /proc/cmdline, so bind mount.
mount -t proc proc "$1/proc"
echo "quiet ostree=/ostree/boot.0 ro" >"$1/override_cmdline"
mount --bind "$1/override_cmdline" "$1/proc/cmdline"
touch "$1/this_is_bootfs"
cp "$(dirname "$this_script")/../ostree-prepare-root" "$1/bin"
}