[PATCH] autofs 4.1.4 no-unlink patch

[Chris Feist <cfeist@redhat.com>]

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Ian,

We've been hearing some reports of autofs removing entire home directories 
when mounts expire.  It appears that this could be some sort of race condition 
in the walk_tree code, where when the function starts the directory is 
unmounted and then autofs unlinks files in the the directory that is supposed 
to be umounted.  I've attached a patch to the rm_unwanted_fn which adds some 
additional checks before we unlink anything, and it prevents autofs from 
unlinking files (since I'm pretty sure that autofs never creates a regular 
file).  Let me know what you think.

Thanks,
Chris

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--- autofs-4.1.4/daemon/automount.c.no-unlink	2005-07-11 13:28:57.000000000 -0500
+++ autofs-4.1.4/daemon/automount.c	2005-07-11 13:50:46.000000000 -0500
@@ -216,16 +216,38 @@ static int walk_tree(const char *base, i
 static int rm_unwanted_fn(const char *file, const struct stat *st, int when, void *arg)
 {
 	int rmsymlink = *(int *) arg;
+	struct stat newst;
 
 	if (when == 0) {
 		if (st->st_dev != ap.dev)
 			return 0;
-	} else {
-		info("rm_unwanted: %s\n", file);
-		if (S_ISDIR(st->st_mode))
-			rmdir(file);
-		else if (!S_ISLNK(st->st_mode) || rmsymlink)
-			unlink(file);
+		return 1;
+	}
+
+	if (lstat(file, &newst)) {
+		crit ("rm_unwanted: unable to stat file, possible race "
+		      "condition.");
+		return 0;
+	}
+
+	if (newst.st_dev != ap.dev) {
+		crit ("rm_unwanted: file %s has the wrong device, possible "
+		      "race condition.",file);
+		return 0;
+	}
+
+	if (S_ISDIR(newst.st_mode)) {
+		if (rmdir(file)) {
+			info ("rm_unwanted: unable to remove directory"
+			      " %s", file);
+			return 0;
+		}
+	} else if (S_ISREG(newst.st_mode)) {
+		crit ("rm_unwanted: attempting to remove files from a mounted "
+		      "directory.");
+		return 0;
+	} else if (S_ISLNK(newst.st_mode) && rmsymlink) {
+		unlink(file);
 	}
 
 	return 1;

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