From efe0be279901006f939cd357ccee47b651c786da Mon Sep 17 00:00:00 2001
From: Seebs <seebs@seebs.net>
Date: Fri, 24 Feb 2017 12:47:38 -0600
Subject: Don't try to record 0-length posix_acl_default xattrs

Based on a submission from Anton Gerasimov <anton@advancedtelematic.com>

On some systems, with some kernel configs, "cp -a" apparently tries to
set an empty ACL list, with a valid header but no contents, which causes
strange and mysterious behavior later if we actually create such an entry.
So filter that out, also sanity-check a couple of other things.

Signed-off-by: Seebs <seebs@seebs.net>

Upstream-Status: Backport

diff --git a/ChangeLog.txt b/ChangeLog.txt
index ae2a6e9..a2d30e9 100644
--- a/ChangeLog.txt
+++ b/ChangeLog.txt
@@ -1,3 +1,6 @@
+2017-02-24:
+	* (seebs) import posix_acl_default fix from Anton Gerasimov
+	  <anton@advancedtelematic.com>
 2017-02-01:
    * (seebs) handle xattr deletion slightly more carefully.
    * (seebs) tag this as 1.8.2
diff --git a/ports/linux/xattr/pseudo_wrappers.c b/ports/linux/xattr/pseudo_wrappers.c
index 46bc053..d69d53e 100644
--- a/ports/linux/xattr/pseudo_wrappers.c
+++ b/ports/linux/xattr/pseudo_wrappers.c
@@ -62,9 +62,9 @@ static int
 posix_permissions(const acl_header *header, int entries, int *extra, int *mode) {
 	int acl_seen = 0;
 	if (le32(header->version) != 2) {
-		pseudo_diag("Fatal: ACL support no available for header version %d.\n",
+		pseudo_diag("Fatal: ACL support not available for header version %d.\n",
 			le32(header->version));
-		return 1;
+		return -1;
 	}
 	*mode = 0;
 	*extra = 0;
@@ -140,12 +140,38 @@ static int shared_setxattr(const char *path, int fd, const char *name, const voi
 	pseudo_debug(PDBGF_XATTR, "setxattr(%s [fd %d], %s => '%.*s')\n",
 		path ? path : "<no path>", fd, name, (int) size, (char *) value);
 
+	/* Filter out erroneous sizes for POSIX ACL
+	 *  see posix_acl_xattr_count in include/linux/posix_acl_xattr.h of Linux source code */
+	/* I don't think there's any posix_acl_* values that aren't in this format */
+	if (!strncmp(name, "system.posix_acl_", 17)) {
+		// ACL is corrupt, issue an error
+		if(size < sizeof(acl_header) || (size - sizeof(acl_header)) % sizeof(acl_entry) != 0) {
+			pseudo_debug(PDBGF_XATTR, "invalid data size for %s: %d\n",
+				name, (int) size);
+			errno = EINVAL;
+			return -1;
+		}
+
+		// ACL is empty, do nothing
+		if((size - sizeof(acl_header)) / sizeof(acl_entry) == 0) {
+			/* on some systems, "cp -a" will attempt to clone the
+			 * posix_acl_default entry for a directory (which would specify
+			 * default ACLs for new files in that directory), but if the
+			 * original was empty, we get a header but no entries. With
+			 * real xattr, that ends up being silently discarded, apparently,
+			 * so we discard it too.
+			 */
+			pseudo_debug(PDBGF_XATTR, "0-length ACL entry %s.\n", name);
+			return 0;
+		}
+	}
 	/* this may be a plain chmod */
 	if (!strcmp(name, "system.posix_acl_access")) {
 		int extra;
 		int mode;
 		int entries = (size - sizeof(acl_header)) / sizeof(acl_entry);
-		if (!posix_permissions(value, entries, &extra, &mode)) {
+		int res = posix_permissions(value, entries, &extra, &mode);
+		if (res == 0) {
 			pseudo_debug(PDBGF_XATTR, "posix_acl_access translated to mode %04o. Remaining attribute(s): %d.\n",
 				mode, extra);
 			buf.st_mode = mode;
@@ -164,8 +190,12 @@ static int shared_setxattr(const char *path, int fd, const char *name, const voi
 			if (!extra) {
 				return 0;
 			}
+		} else if (res == -1) {
+			errno = EOPNOTSUPP;
+			return -1;
 		}
 	}
+
 	if (!strcmp(name, "user.pseudo_data")) {
 		pseudo_debug(PDBGF_XATTR | PDBGF_XATTRDB, "user.pseudo_data xattribute does not get to go in database.\n");
 		return -1;
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