[Devel] [PATCH 04/16][cr][v3]: Restore file_owner info

[Sukadev Bhattiprolu]

Restore the file-owner information for each 'struct file'.  This is
essentially is like a new fcntl(F_SETOWN) and fcntl(F_SETSIG) calls,
except that the pid, uid, euid and signum values are read from the
checkpoint image.

Changelog[v3]:
	- [Oren Laadan]: Ensure find_vpid() found a valid pid before
	  making it the file owner.
Changelog[v2]:
	- [Matt Helsley, Serge Hallyn]: Don't trust uids in checkpoint image.
	  (added CAP_KILL check)
	- Check that signal number read from the checkpoint image is valid.
	  (not sure it is required, since its an incomplete check for tampering)

Signed-off-by: Sukadev Bhattiprolu <sukadev at linux.vnet.ibm.com>
---
 fs/checkpoint.c |   66 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 files changed, 66 insertions(+), 0 deletions(-)

diff --git a/fs/checkpoint.c b/fs/checkpoint.c
index ce1b4af..b5486c1 100644
--- a/fs/checkpoint.c
+++ b/fs/checkpoint.c
@@ -618,6 +618,68 @@ static int attach_file(struct file *file)
 	return fd;
 }
 
+static int restore_file_owner(struct ckpt_ctx *ctx, struct ckpt_hdr_file *h,
+		struct file *file)
+{
+	int ret;
+	struct pid *pid;
+	uid_t uid, euid;
+
+	uid = h->f_owner_uid;
+	euid = h->f_owner_euid;
+
+	ckpt_debug("restore_file_owner(): uid %u, euid %u, pid %d, type %d\n",
+			uid, euid, h->f_owner_pid, h->f_owner_pid_type);
+	/*
+	 * We can't trust the uids in the checkpoint image and normally need
+	 * CAP_KILL. But if the uids match our ids, should be fine since we
+	 * have access to the file.
+	 *
+	 * TODO: Move this check to __f_setown() ?
+	 */
+	ret = -EACCES;
+	if (!capable(CAP_KILL) &&
+			(uid != current_uid() || euid != current_euid())) {
+		ckpt_err(ctx, ret, "image uids [%d, %d] don't match current "
+				"process uids [%d, %d] and no CAP_KILL\n",
+				uid, euid, current_uid(), current_euid());
+		return ret;
+	}
+
+	ret = -EINVAL;
+	if (!valid_signal(h->f_owner_signum)) {
+		ckpt_err(ctx, ret, "Invalid signum %d\n", h->f_owner_signum);
+		return ret;
+	}
+	file->f_owner.signum = h->f_owner_signum;
+
+	rcu_read_lock();
+
+	/*
+	 * If file had a non-NULL owner and we can't find the owner after
+	 * restart, return error.
+	 */
+	pid = find_vpid(h->f_owner_pid);
+	if (h->f_owner_pid && !pid)
+		ret = -ESRCH;
+	else {
+		/*
+		 * TODO: Do we need 'force' to be 1 here or can it be 0 ?
+		 * 	 'force' is used to modify the owner, if one is
+		 * 	 already set. Can it be set when we restart an
+		 * 	 application ?
+		 */
+		ret = __f_setown(file, pid, h->f_owner_pid_type, uid, euid, 1);
+	}
+
+	rcu_read_unlock();
+
+	if (ret < 0)
+		ckpt_err(ctx, ret, "__fsetown_uid() failed\n");
+
+	return ret;
+}
+
 #define CKPT_SETFL_MASK  \
 	(O_APPEND | O_NONBLOCK | O_NDELAY | FASYNC | O_DIRECT | O_NOATIME)
 
@@ -651,6 +713,10 @@ int restore_file_common(struct ckpt_ctx *ctx, struct file *file,
 	if (ret < 0)
 		return ret;
 
+	ret = restore_file_owner(ctx, h, file);
+	if (ret < 0)
+		return ret;
+
 	/*
 	 * Normally f_mode is set by open, and modified only via
 	 * fcntl(), so its value now should match that at checkpoint.
-- 
1.6.0.4

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