CVE-2016-5418 (published 2016-09-21T14:25Z)

The sandboxing code in libarchive 3.2.0 and earlier mishandles hardlink archive entries of non-zero data size, which might allow remote attackers to write to arbitrary files via a crafted archive file.

Severity: MEDIUM
CVSS v2 base score: 5.0 (AV:N/AC:L/Au:N/C:N/I:P/A:N)
CVSS v3 base score: 7.5, HIGH (CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N)

Weakness information:
cwe_id: CWE-20
cwe_name: Improper Input Validation
description: The product receives input or data, but it does
        not validate or incorrectly validates that the input has the
        properties that are required to process the data safely and
        correctly.
extended_description: 
	   Input validation is a frequently-used technique
	   for checking potentially dangerous inputs in order to
	   ensure that the inputs are safe for processing within the
	   code, or when communicating with other components.  When
	   software does not validate input properly, an attacker is
	   able to craft the input in a form that is not expected by
	   the rest of the application. This will lead to parts of the
	   system receiving unintended input, which may result in
	   altered control flow, arbitrary control of a resource, or
	   arbitrary code execution.
	   Input validation is not the only technique for
	   processing input, however.  Other techniques attempt to
	   transform potentially-dangerous input into something safe, such
	   as filtering (CWE-790) - which attempts to remove dangerous
	   inputs - or encoding/escaping (CWE-116), which attempts to
	   ensure that the input is not misinterpreted when it is included
	   in output to another component. Other techniques exist as well
	   (see CWE-138 for more examples.)
	   Input validation can be applied to:
	   
	     raw data - strings, numbers, parameters, file contents, etc.
	     metadata - information about the raw data, such as headers or size
	   
	   Data can be simple or structured.  Structured data
	   can be composed of many nested layers, composed of
	   combinations of metadata and raw data, with other simple or
	   structured data.
	   Many properties of raw data or metadata may need
	   to be validated upon entry into the code, such
	   as:
	   
	     specified quantities such as size, length, frequency, price, rate, number of operations, time, etc.
	     implied or derived quantities, such as the actual size of a file instead of a specified size
	     indexes, offsets, or positions into more complex data structures
	     symbolic keys or other elements into hash tables, associative arrays, etc.
	     well-formedness, i.e. syntactic correctness - compliance with expected syntax 
	     lexical token correctness - compliance with rules for what is treated as a token
	     specified or derived type - the actual type of the input (or what the input appears to be)
	     consistency - between individual data elements, between raw data and metadata, between references, etc.
	     conformance to domain-specific rules, e.g. business logic 
	     equivalence - ensuring that equivalent inputs are treated the same
	     authenticity, ownership, or other attestations about the input, e.g. a cryptographic signature to prove the source of the data
	   
	   Implied or derived properties of data must often
	   be calculated or inferred by the code itself.  Errors in
	   deriving properties may be considered a contributing factor
	   to improper input validation.
	   
	   Note that "input validation" has very different
	   meanings to different people, or within different
	   classification schemes.  Caution must be used when
	   referencing this CWE entry or mapping to it.  For example,
	   some weaknesses might involve inadvertently giving control
	   to an attacker over an input when they should not be able
	   to provide an input at all, but sometimes this is referred
	   to as input validation.
	   Finally, it is important to emphasize that the
	   distinctions between input validation and output escaping
	   are often blurred, and developers must be careful to
	   understand the difference, including how input validation
	   is not always sufficient to prevent vulnerabilities,
	   especially when less stringent data types must be
	   supported, such as free-form text. Consider a SQL injection
	   scenario in which a person's last name is inserted into a
	   query. The name "O'Reilly" would likely pass the validation
	   step since it is a common last name in the English
	   language. However, this valid name cannot be directly
	   inserted into the database because it contains the "'"
	   apostrophe character, which would need to be escaped or
	   otherwise transformed. In this case, removing the
	   apostrophe might reduce the risk of SQL injection, but it
	   would produce incorrect behavior because the wrong name
	   would be recorded.
       
         
cwe_id: CWE-19
cwe_name: Data Processing Errors
description: Weaknesses in this category are typically found in functionality that processes data. Data processing is the manipulation of input to retrieve or save information.

Fix information:
repo_url: https://github.com/libarchive/libarchive
commit_details: repo_url: https://github.com/libarchive/libarchive
author: Tim Kientzle
author_date: 2016-09-11 13:21:57-07:00
msg: Fixes for Issue #745 and Issue #746 from Doran Moppert.
repository: repo_url: https://github.com/libarchive/libarchive
repo_name: libarchive/libarchive
description: Multi-format archive and compression library
repo_language: C
owner: libarchive
file_changes: filename: archive_write_disk_posix.c
change_type: ModificationType.MODIFY
diff: @@ -326,12 +326,14 @@ struct archive_write_disk {
 
 #define HFS_BLOCKS(s)	((s) >> 12)
 
+static int	check_symlinks_fsobj(char *path, int *error_number, struct archive_string *error_string, int flags);
 static int	check_symlinks(struct archive_write_disk *);
 static int	create_filesystem_object(struct archive_write_disk *);
 static struct fixup_entry *current_fixup(struct archive_write_disk *, const char *pathname);
 #if defined(HAVE_FCHDIR) && defined(PATH_MAX)
 static void	edit_deep_directories(struct archive_write_disk *ad);
 #endif
+static int	cleanup_pathname_fsobj(char *path, int *error_number, struct archive_string *error_string, int flags);
 static int	cleanup_pathname(struct archive_write_disk *);
 static int	create_dir(struct archive_write_disk *, char *);
 static int	create_parent_dir(struct archive_write_disk *, char *);
@@ -2014,6 +2016,10 @@ create_filesystem_object(struct archive_write_disk *a)
 	const char *linkname;
 	mode_t final_mode, mode;
 	int r;
+	/* these for check_symlinks_fsobj */
+	char *linkname_copy;	/* non-const copy of linkname */
+	struct archive_string error_string;
+	int error_number;
 
 	/* We identify hard/symlinks according to the link names. */
 	/* Since link(2) and symlink(2) don't handle modes, we're done here. */
@@ -2022,6 +2028,27 @@ create_filesystem_object(struct archive_write_disk *a)
 #if !HAVE_LINK
 		return (EPERM);
 #else
+		archive_string_init(&error_string);
+		linkname_copy = strdup(linkname);
+		if (linkname_copy == NULL) {
+		    return (EPERM);
+		}
+		/* TODO: consider using the cleaned-up path as the link target? */
+		r = cleanup_pathname_fsobj(linkname_copy, &error_number, &error_string, a->flags);
+		if (r != ARCHIVE_OK) {
+			archive_set_error(&a->archive, error_number, "%s", error_string.s);
+			free(linkname_copy);
+			/* EPERM is more appropriate than error_number for our callers */
+			return (EPERM);
+		}
+		r = check_symlinks_fsobj(linkname_copy, &error_number, &error_string, a->flags);
+		if (r != ARCHIVE_OK) {
+			archive_set_error(&a->archive, error_number, "%s", error_string.s);
+			free(linkname_copy);
+			/* EPERM is more appropriate than error_number for our callers */
+			return (EPERM);
+		}
+		free(linkname_copy);
 		r = link(linkname, a->name) ? errno : 0;
 		/*
 		 * New cpio and pax formats allow hardlink entries
@@ -2362,115 +2389,228 @@ current_fixup(struct archive_write_disk *a, const char *pathname)
  * recent paths.
  */
 /* TODO: Extend this to support symlinks on Windows Vista and later. */
+
+/*
+ * Checks the given path to see if any elements along it are symlinks.  Returns
+ * ARCHIVE_OK if there are none, otherwise puts an error in errmsg.
+ */
 static int
-check_symlinks(struct archive_write_disk *a)
+check_symlinks_fsobj(char *path, int *error_number, struct archive_string *error_string, int flags)
 {
 #if !defined(HAVE_LSTAT)
 	/* Platform doesn't have lstat, so we can't look for symlinks. */
 	(void)a; /* UNUSED */
+	(void)path; /* UNUSED */
+	(void)error_number; /* UNUSED */
+	(void)error_string; /* UNUSED */
+	(void)flags; /* UNUSED */
 	return (ARCHIVE_OK);
 #else
-	char *pn;
+	int res = ARCHIVE_OK;
+	char *tail;
+	char *head;
+	int last;
 	char c;
 	int r;
 	struct stat st;
+	int restore_pwd;
+
+	/* Nothing to do here if name is empty */
+	if(path[0] == '\0')
+	    return (ARCHIVE_OK);
 
 	/*
 	 * Guard against symlink tricks.  Reject any archive entry whose
 	 * destination would be altered by a symlink.
+	 *
+	 * Walk the filename in chunks separated by '/'.  For each segment:
+	 *  - if it doesn't exist, continue
+	 *  - if it's symlink, abort or remove it
+	 *  - if it's a directory and it's not the last chunk, cd into it
+	 * As we go:
+	 *  head points to the current (relative) path
+	 *  tail points to the temporary \0 terminating the segment we're currently examining
+	 *  c holds what used to be in *tail
+	 *  last is 1 if this is the last tail
 	 */
-	/* Whatever we checked last time doesn't need to be re-checked. */
-	pn = a->name;
-	if (archive_strlen(&(a->path_safe)) > 0) {
-		char *p = a->path_safe.s;
-		while ((*pn != '\0') && (*p == *pn))
-			++p, ++pn;
-	}
+	restore_pwd = open(".", O_RDONLY | O_BINARY | O_CLOEXEC);
+	__archive_ensure_cloexec_flag(restore_pwd);
+	if (restore_pwd < 0)
+		return (ARCHIVE_FATAL);
+	head = path;
+	tail = path;
+	last = 0;
+	/* TODO: reintroduce a safe cache here? */
 	/* Skip the root directory if the path is absolute. */
-	if(pn == a->name && pn[0] == '/')
-		++pn;
-	c = pn[0];
-	/* Keep going until we've checked the entire name. */
-	while (pn[0] != '\0' && (pn[0] != '/' || pn[1] != '\0')) {
+	if(tail == path && tail[0] == '/')
+		++tail;
+	/* Keep going until we've checked the entire name.
+	 * head, tail, path all alias the same string, which is
+	 * temporarily zeroed at tail, so be careful restoring the
+	 * stashed (c=tail[0]) for error messages.
+	 * Exiting the loop with break is okay; continue is not.
+	 */
+	while (!last) {
+		/* Skip the separator we just consumed, plus any adjacent ones */
+		while (*tail == '/')
+		    ++tail;
 		/* Skip the next path element. */
-		while (*pn != '\0' && *pn != '/')
-			++pn;
-		c = pn[0];
-		pn[0] = '\0';
+		while (*tail != '\0' && *tail != '/')
+			++tail;
+		/* is this the last path component? */
+		last = (tail[0] == '\0') || (tail[0] == '/' && tail[1] == '\0');
+		/* temporarily truncate the string here */
+		c = tail[0];
+		tail[0] = '\0';
 		/* Check that we haven't hit a symlink. */
-		r = lstat(a->name, &st);
+		r = lstat(head, &st);
 		if (r != 0) {
+			tail[0] = c;
 			/* We've hit a dir that doesn't exist; stop now. */
 			if (errno == ENOENT) {
 				break;
 			} else {
-				/* Note: This effectively disables deep directory
+				/* Treat any other error as fatal - best to be paranoid here
+				 * Note: This effectively disables deep directory
 				 * support when security checks are enabled.
 				 * Otherwise, very long pathnames that trigger
 				 * an error here could evade the sandbox.
 				 * TODO: We could do better, but it would probably
 				 * require merging the symlink checks with the
 				 * deep-directory editing. */
-				return (ARCHIVE_FAILED);
+				if (error_number) *error_number = errno;
+				if (error_string)
+					archive_string_sprintf(error_string,
+							"Could not stat %s",
+							path);
+				res = ARCHIVE_FAILED;
+				break;
+			}
+		} else if (S_ISDIR(st.st_mode)) {
+			if (!last) {
+				if (chdir(head) != 0) {
+					tail[0] = c;
+					if (error_number) *error_number = errno;
+					if (error_string)
+						archive_string_sprintf(error_string,
+								"Could not chdir %s",
+								path);
+					res = (ARCHIVE_FATAL);
+					break;
+				}
+				/* Our view is now from inside this dir: */
+				head = tail + 1;
 			}
 		} else if (S_ISLNK(st.st_mode)) {
-			if (c == '\0') {
+			if (last) {
 				/*
 				 * Last element is symlink; remove it
 				 * so we can overwrite it with the
 				 * item being extracted.
 				 */
-				if (unlink(a->name)) {
-					archive_set_error(&a->archive, errno,
-					    "Could not remove symlink %s",
-					    a->name);
-					pn[0] = c;
-					return (ARCHIVE_FAILED);
+				if (unlink(head)) {
+					tail[0] = c;
+					if (error_number) *error_number = errno;
+					if (error_string)
+						archive_string_sprintf(error_string,
+								"Could not remove symlink %s",
+								path);
+					res = ARCHIVE_FAILED;
+					break;
 				}
-				a->pst = NULL;
 				/*
 				 * Even if we did remove it, a warning
 				 * is in order.  The warning is silly,
 				 * though, if we're just replacing one
 				 * symlink with another symlink.
 				 */
-				if (!S_ISLNK(a->mode)) {
-					archive_set_error(&a->archive, 0,
-					    "Removing symlink %s",
-					    a->name);
+				tail[0] = c;
+				/* FIXME:  not sure how important this is to restore
+				if (!S_ISLNK(path)) {
+					if (error_number) *error_number = 0;
+					if (error_string)
+						archive_string_sprintf(error_string,
+								"Removing symlink %s",
+								path);
 				}
+				*/
 				/* Symlink gone.  No more problem! */
-				pn[0] = c;
-				return (0);
-			} else if (a->flags & ARCHIVE_EXTRACT_UNLINK) {
+				res = ARCHIVE_OK;
+				break;
+			} else if (flags & ARCHIVE_EXTRACT_UNLINK) {
 				/* User asked us to remove problems. */
-				if (unlink(a->name) != 0) {
-					archive_set_error(&a->archive, 0,
-					    "Cannot remove intervening symlink %s",
-					    a->name);
-					pn[0] = c;
-					return (ARCHIVE_FAILED);
+				if (unlink(head) != 0) {
+					tail[0] = c;
+					if (error_number) *error_number = 0;
+					if (error_string)
+						archive_string_sprintf(error_string,
+								"Cannot remove intervening symlink %s",
+								path);
+					res = ARCHIVE_FAILED;
+					break;
 				}
-				a->pst = NULL;
+				tail[0] = c;
 			} else {
-				archive_set_error(&a->archive, 0,
-				    "Cannot extract through symlink %s",
-				    a->name);
-				pn[0] = c;
-				return (ARCHIVE_FAILED);
+				tail[0] = c;
+				if (error_number) *error_number = 0;
+				if (error_string)
+					archive_string_sprintf(error_string,
+							"Cannot extract through symlink %s",
+							path);
+				res = ARCHIVE_FAILED;
+				break;
 			}
 		}
-		pn[0] = c;
-		if (pn[0] != '\0')
-			pn++; /* Advance to the next segment. */
+		/* be sure to always maintain this */
+		tail[0] = c;
+		if (tail[0] != '\0')
+			tail++; /* Advance to the next segment. */
 	}
-	pn[0] = c;
-	/* We've checked and/or cleaned the whole path, so remember it. */
-	archive_strcpy(&a->path_safe, a->name);
-	return (ARCHIVE_OK);
+	/* Catches loop exits via break */
+	tail[0] = c;
+#ifdef HAVE_FCHDIR
+	/* If we changed directory above, restore it here. */
+	if (restore_pwd >= 0) {
+		r = fchdir(restore_pwd);
+		if (r != 0) {
+			if(error_number) *error_number = errno;
+			if(error_string)
+				archive_string_sprintf(error_string,
+						"chdir() failure");
+		}
+		close(restore_pwd);
+		restore_pwd = -1;
+		if (r != 0) {
+			res = (ARCHIVE_FATAL);
+		}
+	}
+#endif
+	/* TODO: reintroduce a safe cache here? */
+	return res;
 #endif
 }
 
+/*
+ * Check a->name for symlinks, returning ARCHIVE_OK if its clean, otherwise
+ * calls archive_set_error and returns ARCHIVE_{FATAL,FAILED}
+ */
+static int
+check_symlinks(struct archive_write_disk *a)
+{
+	struct archive_string error_string;
+	int error_number;
+	int rc;
+	archive_string_init(&error_string);
+	rc = check_symlinks_fsobj(a->name, &error_number, &error_string, a->flags);
+	if (rc != ARCHIVE_OK) {
+		archive_set_error(&a->archive, error_number, "%s", error_string.s);
+	}
+	archive_string_free(&error_string);
+	a->pst = NULL;	/* to be safe */
+	return rc;
+}
+
+
 #if defined(__CYGWIN__)
 /*
  * 1. Convert a path separator from '\' to '/' .
@@ -2544,15 +2684,17 @@ cleanup_pathname_win(struct archive_write_disk *a)
  * is set) if the path is absolute.
  */
 static int
-cleanup_pathname(struct archive_write_disk *a)
+cleanup_pathname_fsobj(char *path, int *error_number, struct archive_string *error_string, int flags)
 {
 	char *dest, *src;
 	char separator = '\0';
 
-	dest = src = a->name;
+	dest = src = path;
 	if (*src == '\0') {
-		archive_set_error(&a->archive, ARCHIVE_ERRNO_MISC,
-		    "Invalid empty pathname");
+		if (error_number) *error_number = ARCHIVE_ERRNO_MISC;
+		if (error_string)
+		    archive_string_sprintf(error_string,
+			    "Invalid empty pathname");
 		return (ARCHIVE_FAILED);
 	}
 
@@ -2561,9 +2703,11 @@ cleanup_pathname(struct archive_write_disk *a)
 #endif
 	/* Skip leading '/'. */
 	if (*src == '/') {
-		if (a->flags & ARCHIVE_EXTRACT_SECURE_NOABSOLUTEPATHS) {
-			archive_set_error(&a->archive, ARCHIVE_ERRNO_MISC,
-			                  "Path is absolute");
+		if (flags & ARCHIVE_EXTRACT_SECURE_NOABSOLUTEPATHS) {
+			if (error_number) *error_number = ARCHIVE_ERRNO_MISC;
+			if (error_string)
+			    archive_string_sprintf(error_string,
+				    "Path is absolute");
 			return (ARCHIVE_FAILED);
 		}
 
@@ -2590,10 +2734,11 @@ cleanup_pathname(struct archive_write_disk *a)
 			} else if (src[1] == '.') {
 				if (src[2] == '/' || src[2] == '\0') {
 					/* Conditionally warn about '..' */
-					if (a->flags & ARCHIVE_EXTRACT_SECURE_NODOTDOT) {
-						archive_set_error(&a->archive,
-						    ARCHIVE_ERRNO_MISC,
-						    "Path contains '..'");
+					if (flags & ARCHIVE_EXTRACT_SECURE_NODOTDOT) {
+						if (error_number) *error_number = ARCHIVE_ERRNO_MISC;
+						if (error_string)
+						    archive_string_sprintf(error_string,
+							    "Path contains '..'");
 						return (ARCHIVE_FAILED);
 					}
 				}
@@ -2624,7 +2769,7 @@ cleanup_pathname(struct archive_write_disk *a)
 	 * We've just copied zero or more path elements, not including the
 	 * final '/'.
 	 */
-	if (dest == a->name) {
+	if (dest == path) {
 		/*
 		 * Nothing got copied.  The path must have been something
 		 * like '.' or '/' or './' or '/././././/./'.
@@ -2639,6 +2784,21 @@ cleanup_pathname(struct archive_write_disk *a)
 	return (ARCHIVE_OK);
 }
 
+static int
+cleanup_pathname(struct archive_write_disk *a)
+{
+	struct archive_string error_string;
+	int error_number;
+	int rc;
+	archive_string_init(&error_string);
+	rc = cleanup_pathname_fsobj(a->name, &error_number, &error_string, a->flags);
+	if (rc != ARCHIVE_OK) {
+		archive_set_error(&a->archive, error_number, "%s", error_string.s);
+	}
+	archive_string_free(&error_string);
+	return rc;
+}
+
 /*
  * Create the parent directory of the specified path, assuming path
  * is already in mutable storage.

programming_language: C