combined security fixes for 3.4.3 release

.github/workflows/cygwin-build.yml

@@ -39,7 +39,7 @@ jobs:
     - name: info
       run: bash -c '/usr/local/bin/rsync --version'
     - name: check
-      run: bash -c 'RSYNC_EXPECT_SKIPPED=acls-default,acls,chown,devices,dir-sgid,open-noatime,protected-regular,simd-checksum,symlink-dirlink-basis make check'
+      run: bash -c 'RSYNC_EXPECT_SKIPPED=acls-default,acls,bare-do-open-symlink-race,chdir-symlink-race,chmod-symlink-race,chown,daemon-chroot-acl,devices,dir-sgid,open-noatime,protected-regular,sender-flist-symlink-leak,simd-checksum,symlink-dirlink-basis make check'
     - name: ssl file list
       run: bash -c 'PATH="/usr/local/bin:$PATH" rsync-ssl --no-motd download.samba.org::rsyncftp/ || true'
     - name: save artifact

.github/workflows/macos-build.yml

@@ -41,7 +41,7 @@ jobs:
     - name: info
       run: rsync --version
     - name: check
-      run: sudo RSYNC_EXPECT_SKIPPED=acls-default,chmod-temp-dir,chown-fake,devices-fake,dir-sgid,open-noatime,protected-regular,simd-checksum,xattrs-hlink,xattrs make check
+      run: sudo RSYNC_EXPECT_SKIPPED=acls-default,chmod-temp-dir,chown-fake,daemon-chroot-acl,devices-fake,dir-sgid,open-noatime,protected-regular,simd-checksum,xattrs-hlink,xattrs make check
     - name: ssl file list
       run: rsync-ssl --no-motd download.samba.org::rsyncftp/ || true
     - name: save artifact

Makefile.in

@@ -57,13 +57,13 @@ TLS_OBJ = tls.o syscall.o util2.o t_stub.o lib/compat.o lib/snprintf.o lib/perms
 
 # Programs we must have to run the test cases
 CHECK_PROGS = rsync$(EXEEXT) tls$(EXEEXT) getgroups$(EXEEXT) getfsdev$(EXEEXT) \
-	testrun$(EXEEXT) trimslash$(EXEEXT) t_unsafe$(EXEEXT) wildtest$(EXEEXT) \
-	simdtest$(EXEEXT)
+	testrun$(EXEEXT) trimslash$(EXEEXT) t_unsafe$(EXEEXT) t_chmod_secure$(EXEEXT) \
+	t_secure_relpath$(EXEEXT) wildtest$(EXEEXT) simdtest$(EXEEXT)
 
 CHECK_SYMLINKS = testsuite/chown-fake.test testsuite/devices-fake.test testsuite/xattrs-hlink.test
 
 # Objects for CHECK_PROGS to clean
-CHECK_OBJS=tls.o testrun.o getgroups.o getfsdev.o t_stub.o t_unsafe.o trimslash.o wildtest.o
+CHECK_OBJS=tls.o testrun.o getgroups.o getfsdev.o t_stub.o t_unsafe.o t_chmod_secure.o t_secure_relpath.o trimslash.o wildtest.o
 
 # note that the -I. is needed to handle config.h when using VPATH
 .c.o:
@@ -179,6 +179,14 @@ T_UNSAFE_OBJ = t_unsafe.o syscall.o util1.o util2.o t_stub.o lib/compat.o lib/sn
 t_unsafe$(EXEEXT): $(T_UNSAFE_OBJ)
 	$(CC) $(CFLAGS) $(LDFLAGS) -o $@ $(T_UNSAFE_OBJ) $(LIBS)
 
+T_CHMOD_SECURE_OBJ = t_chmod_secure.o syscall.o util1.o util2.o t_stub.o lib/compat.o lib/snprintf.o lib/wildmatch.o lib/permstring.o
+t_chmod_secure$(EXEEXT): $(T_CHMOD_SECURE_OBJ)
+	$(CC) $(CFLAGS) $(LDFLAGS) -o $@ $(T_CHMOD_SECURE_OBJ) $(LIBS)
+
+T_SECURE_RELPATH_OBJ = t_secure_relpath.o syscall.o util1.o util2.o t_stub.o lib/compat.o lib/snprintf.o lib/wildmatch.o lib/permstring.o
+t_secure_relpath$(EXEEXT): $(T_SECURE_RELPATH_OBJ)
+	$(CC) $(CFLAGS) $(LDFLAGS) -o $@ $(T_SECURE_RELPATH_OBJ) $(LIBS)
+
 .PHONY: conf
 conf: configure.sh config.h.in
 

NEWS.md

@@ -1,7 +1,122 @@
-# NEWS for rsync 3.4.3 (UNRELEASED)
+# NEWS for rsync 3.4.3 (20 May 2026)
 
 ## Changes in this version:
 
+### SECURITY FIXES:
+
+Six CVEs are fixed in this release.  All six are assigned by
+VulnCheck as CNA.  Affected versions are 3.4.2 and earlier in every
+case.  Three of the six (CVE-2026-29518, CVE-2026-43617,
+CVE-2026-43619) require non-default daemon configuration to reach:
+the first and third need `use chroot = no` for a module, the second
+needs `daemon chroot = ...` set in rsyncd.conf.  Two (CVE-2026-43618,
+CVE-2026-43620) are reachable from a normal pull or a normal
+authenticated daemon connection.  The sixth (CVE-2026-45232) is
+reachable only when `RSYNC_PROXY` is set and the proxy (or a MITM)
+returns a pathological response.  Many thanks to the external
+researchers who reported these issues.
+
+- CVE-2026-29518 (CVSS v4.0 7.3, HIGH): TOCTOU symlink race condition
+  allowing local privilege escalation in daemon mode without chroot.
+  An rsync daemon configured with "use chroot = no" was exposed to a
+  time-of-check / time-of-use race on parent path components: a local
+  attacker with write access to a module could replace a parent
+  directory component with a symlink between the receiver's check and
+  its open(), redirecting reads (basis-file disclosure) and writes
+  (file overwrite) outside the module.  Default "use chroot = yes" is
+  not exposed.  `secure_relative_open()` (added in 3.4.0 for
+  CVE-2024-12086) was previously unused in the daemon-no-chroot
+  case; the fix enables it there and reroutes the sender's
+  read-path opens through it.  Reported by Nullx3D (Batuhan Sancak),
+  Damien Neil and Michael Stapelberg.
+
+- CVE-2026-43617 (CVSS v3.1 4.8, MEDIUM): Hostname/ACL bypass on an
+  rsync daemon configured with `daemon chroot = /X` in rsyncd.conf
+  when the chroot tree lacks DNS resolution support.  The
+  reverse-DNS lookup of the connecting client was performed *after*
+  the daemon chroot had been entered; if /X did not contain the
+  libc resolver fixtures (`/etc/resolv.conf`, `/etc/nsswitch.conf`,
+  `/etc/hosts`, NSS service modules) the lookup failed and the
+  connecting hostname was set to "UNKNOWN", causing hostname-based
+  deny rules to silently fail open.  IP-based ACLs are unaffected.
+  The per-module `use chroot` setting is unrelated to this issue.
+  The fix performs the lookup before entering the daemon chroot.
+  Reported by MegaManSec.
+
+- CVE-2026-43618 (CVSS v3.1 8.1, HIGH): Integer overflow in the
+  compressed-token decoder enabling remote memory disclosure to an
+  authenticated daemon peer.  The receiver accumulated a 32-bit
+  signed counter without overflow checking; a malicious sender could
+  trigger an overflow that, with careful manipulation, leaked process
+  memory contents to the attacker -- environment variables,
+  passwords, heap and library pointers -- significantly weakening
+  ASLR.  The fix bounds the counter and adds wire-input validation in
+  several adjacent places (defence-in-depth).  Workaround for older
+  releases: `refuse options = compress` in rsyncd.conf.  Reported by
+  Omar Elsayed.
+
+- CVE-2026-43619 (CVSS v3.1 6.3, MEDIUM): Symlink races on path-based
+  system calls in "use chroot = no" daemon mode (generalisation of
+  CVE-2026-29518).  Earlier fixes for symlink races on the receiver's
+  open() call missed the same race class on every other path-based
+  system call: chmod, lchown, utimes, rename, unlink, mkdir, symlink,
+  mknod, link, rmdir and lstat.  The fix routes each affected
+  path-based syscall through a parent dirfd opened under
+  RESOLVE_BENEATH-equivalent kernel-enforced confinement (openat2 on
+  Linux 5.6+, O_RESOLVE_BENEATH on FreeBSD 13+ and macOS 15+,
+  per-component O_NOFOLLOW walk elsewhere).  Default "use chroot =
+  yes" is not exposed.  Reported by Andrew Tridgell as a follow-on
+  audit of CVE-2026-29518.
+
+- CVE-2026-43620 (CVSS v3.1 6.5, MEDIUM): Out-of-bounds read in the
+  receiver's recv_files() enabling remote denial-of-service of any
+  client pulling from a malicious server (incomplete fix of commit
+  797e17f).  The earlier parent_ndx<0 guard added to send_files() was
+  not applied to the visually-identical block in recv_files().  A
+  malicious rsync server can drive any connecting client into a
+  deterministic SIGSEGV by setting CF_INC_RECURSE in the
+  compatibility flags and sending a crafted file list and transfer
+  record.  inc_recurse is the protocol-30+ default, so no special
+  options are required on the victim.  Workaround for older
+  releases: `--no-inc-recursive` on the client.  Reported by Pratham
+  Gupta.
+
+- CVE-2026-45232 (CVSS v3.1 3.1, LOW): Off-by-one out-of-bounds stack
+  write in the rsync client's HTTP CONNECT proxy handler
+  (`establish_proxy_connection()` in `socket.c`).  After issuing the
+  CONNECT request, rsync read the proxy's first response line one
+  byte at a time into a 1024-byte stack buffer with the bound
+  `cp < &buffer[sizeof buffer - 1]`.  If the proxy (or a MITM in
+  front of it) returned 1023+ bytes on that first line without a
+  newline terminator, `cp` exited the loop pointing at a buffer slot
+  the loop never wrote, leaving `*cp` holding stale stack data from
+  the earlier `snprintf()` of the outgoing CONNECT request.  The
+  post-loop logic then wrote a single `\0` one byte past the end of
+  the buffer on the stack.  Reach is client-side only, and only when
+  `RSYNC_PROXY` is set so rsync tunnels an `rsync://` connection
+  through an HTTP CONNECT proxy.  The written byte is always `\0`
+  and the offset is fixed by the buffer size, not attacker-chosen,
+  so this is not an arbitrary-write primitive: practical impact is
+  corruption of one adjacent stack byte and possible later
+  misbehaviour or crash.  The fix detects the "buffer filled without
+  finding `\n`" case explicitly by position and refuses the response
+  with "proxy response line too long".  Reported by Aisle Research
+  via Michal Ruprich (rsync-3.4.1-2.el10 QE).
+
+In addition to the six CVE fixes, this release adds defence-in-depth
+hardening on several adjacent paths: bounded wire-supplied counts and
+lengths in flist/io/acls/xattrs, a guard against length underflow in
+cumulative `snprintf()` callers, a parent block-index bounds check on
+the receiver, a NULL check in `read_delay_line()`, a lower ceiling on
+`MAX_WIRE_DEL_STAT` to avoid signed-int overflow in the
+`read_del_stats()` accumulator, rejection of hyphen-prefixed
+remote-shell hostnames (defence-in-depth against argv-injection in
+tooling that forwards untrusted input into the hostspec position;
+reported by Aisle Research via Michal Ruprich), and a NULL-check on
+`localtime_r()` in `timestring()` to keep a malicious server from
+crashing the client by advertising a file with an out-of-range
+modtime.
+
 ### BUG FIXES:
 
 - Fixed a regression introduced by the 3.4.0 secure_relative_open()
@@ -37,14 +152,33 @@
   with protocol < 29, top-level files). The test skips on
   platforms without a RESOLVE_BENEATH equivalent.
 
-- runtests.py now errors early with a clear message when the test
-  helper programs (`tls`, `trimslash`, `t_unsafe`, `wildtest`,
-  `getgroups`, `getfsdev`) are missing, instead of letting many
-  tests fail with confusing "not found" errors.
+- Added regression tests for the new security fixes:
+  `chmod-symlink-race.test`, `chdir-symlink-race.test`,
+  `bare-do-open-symlink-race.test`, `alt-dest-symlink-race.test`,
+  `copy-dest-source-symlink.test`, `sender-flist-symlink-leak.test`,
+  `secure-relpath-validation.test`, `daemon-chroot-acl.test` and
+  `daemon-refuse-compress.test`. The symlink-race tests skip on
+  Cygwin, Solaris, OpenBSD and NetBSD (no RESOLVE_BENEATH
+  equivalent on those platforms).
+
+- runtests.py now errors early with a clear message when any of
+  the test helper programs (`tls`, `trimslash`, `t_unsafe`,
+  `t_chmod_secure`, `t_secure_relpath`, `wildtest`, `getgroups`,
+  `getfsdev`) are missing, instead of letting many tests fail with
+  confusing "not found" errors.
 
 - Added OpenBSD and NetBSD CI jobs that run `make check` on those
   platforms.
 
+- Added Ubuntu 22.04 and AlmaLinux 8 CI workflows so future
+  backports to the two mainstream LTS families build and test on
+  the same CI surface as trunk.
+
+- testsuite/protected-regular.test now runs unprivileged via
+  `unshare` with user-namespace UID mapping, falling back to skip
+  if `unshare`/`uidmap` is not available; previously it required
+  real root.
+
 - Added `symlink-dirlink-basis` to the Cygwin CI's expected-skipped
   list.
 
@@ -5035,7 +5169,7 @@ to develop and test fixes.
 
 | RELEASE DATE | VER.   | DATE OF COMMIT\* | PROTOCOL    |
 |--------------|--------|------------------|-------------|
-| ?? ??? 2026  | 3.4.3  |                  | 32          |
+| 20 May 2026  | 3.4.3  |                  | 32          |
 | 28 Apr 2026  | 3.4.2  |                  | 32          |
 | 16 Jan 2025  | 3.4.1  |                  | 32          |
 | 15 Jan 2025  | 3.4.0  | 15 Jan 2025      | 32          |

acls.c

@@ -697,7 +697,7 @@ static uint32 recv_acl_access(int f, uchar *name_follows_ptr)
 static uchar recv_ida_entries(int f, ida_entries *ent)
 {
 	uchar computed_mask_bits = 0;
-	int i, count = read_varint(f);
+	int i, count = read_varint_bounded(f, 0, MAX_WIRE_ACL_COUNT, "ACL count");
 
 	ent->idas = count ? new_array(id_access, count) : NULL;
 	ent->count = count;

backup.c

@@ -39,7 +39,7 @@ static int validate_backup_dir(void)
 {
 	STRUCT_STAT st;
 
-	if (do_lstat(backup_dir_buf, &st) < 0) {
+	if (do_lstat_at(backup_dir_buf, &st) < 0) {
 		if (errno == ENOENT)
 			return 0;
 		rsyserr(FERROR, errno, "backup lstat %s failed", backup_dir_buf);
@@ -98,7 +98,7 @@ static BOOL copy_valid_path(const char *fname)
 	for ( ; b; name = b + 1, b = strchr(name, '/')) {
 		*b = '\0';
 
-		while (do_mkdir(backup_dir_buf, ACCESSPERMS) < 0) {
+		while (do_mkdir_at(backup_dir_buf, ACCESSPERMS) < 0) {
 			if (errno == EEXIST) {
 				val = validate_backup_dir();
 				if (val > 0)
@@ -197,7 +197,7 @@ static inline int link_or_rename(const char *from, const char *to,
 		if (IS_SPECIAL(stp->st_mode) || IS_DEVICE(stp->st_mode))
 			return 0; /* Use copy code. */
 #endif
-		if (do_link(from, to) == 0) {
+		if (do_link_at(from, to) == 0) {
 			if (DEBUG_GTE(BACKUP, 1))
 				rprintf(FINFO, "make_backup: HLINK %s successful.\n", from);
 			return 2;
@@ -207,7 +207,7 @@ static inline int link_or_rename(const char *from, const char *to,
 			return 0;
 	}
 #endif
-	if (do_rename(from, to) == 0) {
+	if (do_rename_at(from, to) == 0) {
 		if (stp->st_nlink > 1 && !S_ISDIR(stp->st_mode)) {
 			/* If someone has hard-linked the file into the backup
 			 * dir, rename() might return success but do nothing! */
@@ -246,7 +246,7 @@ int make_backup(const char *fname, BOOL prefer_rename)
 		goto success;
 	if (errno == EEXIST || errno == EISDIR) {
 		STRUCT_STAT bakst;
-		if (do_lstat(buf, &bakst) == 0) {
+		if (do_lstat_at(buf, &bakst) == 0) {
 			int flags = get_del_for_flag(bakst.st_mode) | DEL_FOR_BACKUP | DEL_RECURSE;
 			if (delete_item(buf, bakst.st_mode, flags) != 0)
 				return 0;
@@ -277,7 +277,7 @@ int make_backup(const char *fname, BOOL prefer_rename)
 	/* Check to see if this is a device file, or link */
 	if ((am_root && preserve_devices && IS_DEVICE(file->mode))
 	 || (preserve_specials && IS_SPECIAL(file->mode))) {
-		if (do_mknod(buf, file->mode, sx.st.st_rdev) < 0)
+		if (do_mknod_at(buf, file->mode, sx.st.st_rdev) < 0)
 			rsyserr(FERROR, errno, "mknod %s failed", full_fname(buf));
 		else if (DEBUG_GTE(BACKUP, 1))
 			rprintf(FINFO, "make_backup: DEVICE %s successful.\n", fname);
@@ -294,7 +294,7 @@ int make_backup(const char *fname, BOOL prefer_rename)
 			}
 			ret = 2;
 		} else {
-			if (do_symlink(sl, buf) < 0)
+			if (do_symlink_at(sl, buf) < 0)
 				rsyserr(FERROR, errno, "link %s -> \"%s\"", full_fname(buf), sl);
 			else if (DEBUG_GTE(BACKUP, 1))
 				rprintf(FINFO, "make_backup: SYMLINK %s successful.\n", fname);

cleanup.c

@@ -198,7 +198,7 @@ NORETURN void _exit_cleanup(int code, const char *file, int line)
 		switch_step++;
 
 		if (cleanup_fname)
-			do_unlink(cleanup_fname);
+			do_unlink_at(cleanup_fname);
 		if (exit_code)
 			kill_all(SIGUSR1);
 		if (cleanup_pid && cleanup_pid == getpid()) {

clientserver.c

@@ -30,6 +30,7 @@ extern int list_only;
 extern int am_sender;
 extern int am_server;
 extern int am_daemon;
+extern int am_chrooted;
 extern int am_root;
 extern int msgs2stderr;
 extern int rsync_port;
@@ -38,6 +39,7 @@ extern int ignore_errors;
 extern int preserve_xattrs;
 extern int kluge_around_eof;
 extern int munge_symlinks;
+extern int use_secure_symlinks;
 extern int open_noatime;
 extern int sanitize_paths;
 extern int numeric_ids;
@@ -983,6 +985,7 @@ static int rsync_module(int f_in, int f_out, int i, const char *addr, const char
 			io_printf(f_out, "@ERROR: chroot failed\n");
 			return -1;
 		}
+		am_chrooted = 1;
 		module_chdir = module_dir;
 	}
 
@@ -1005,6 +1008,15 @@ static int rsync_module(int f_in, int f_out, int i, const char *addr, const char
 		}
 	}
 
+	/* Enable secure symlink handling for any non-chrooted daemon module.
+	 * This prevents TOCTOU race attacks where an attacker could switch a
+	 * directory to a symlink between path validation and file open.
+	 * Match the gate used by the do_*_at() wrappers in syscall.c
+	 * (am_daemon && !am_chrooted) -- the protection has nothing to do
+	 * with symlink munging, so a module configured with
+	 * "munge symlinks = false" must still get the secure-open path. */
+	use_secure_symlinks = am_daemon && !am_chrooted;
+
 	if (gid_list.count) {
 		gid_t *gid_array = gid_list.items;
 		if (setgid(gid_array[0])) {
@@ -1300,6 +1312,28 @@ int start_daemon(int f_in, int f_out)
 	if (lp_proxy_protocol() && !read_proxy_protocol_header(f_in))
 		return -1;
 
+	/* Do reverse DNS lookup before chroot/setuid. The result is cached,
+	 * so the later client_name() call will use this cached value. This
+	 * ensures hostname-based ACLs work even when DNS is unavailable
+	 * after chroot.
+	 *
+	 * "reverse lookup" can be set globally OR per-module, so we also
+	 * scan each module: a deployment with "reverse lookup = no" in the
+	 * global section but "reverse lookup = yes" in a specific module
+	 * still triggers a post-chroot lookup at access-check time
+	 * (rsync_module() in this file), which would also fail in the
+	 * chroot and turn hostname-based deny rules into silent bypasses. */
+	{
+		int need_reverse = lp_reverse_lookup(-1);
+		int j, num_modules = lp_num_modules();
+		for (j = 0; !need_reverse && j < num_modules; j++) {
+			if (lp_reverse_lookup(j))
+				need_reverse = 1;
+		}
+		if (need_reverse)
+			(void)client_name(client_addr(f_in));
+	}
+
 	p = lp_daemon_chroot();
 	if (*p) {
 		log_init(0); /* Make use we've initialized syslog before chrooting. */
@@ -1308,6 +1342,19 @@ int start_daemon(int f_in, int f_out)
 			rsyserr(FLOG, errno, "daemon chroot(\"%s\") failed", p);
 			return -1;
 		}
+		/* Deliberately do NOT set am_chrooted here.  am_chrooted
+		 * gates the per-module symlink-race defenses
+		 * (secure_relative_open() and the do_*_at() wrappers in
+		 * syscall.c) and means "the kernel is enforcing path
+		 * confinement at the module boundary".  The daemon chroot
+		 * confines path resolution to the daemon-chroot directory,
+		 * not to any individual module path -- modules sharing the
+		 * daemon chroot are still distinguishable filesystem
+		 * subtrees and a sender-controlled symlink in module A
+		 * could redirect a syscall to module B (or to other files
+		 * inside the daemon chroot) without the per-module
+		 * defenses.  Leave am_chrooted=0 here so secure_relative_open()
+		 * still fires for "use chroot = no" modules. */
 		if (chdir("/") < 0) {
 			rsyserr(FLOG, errno, "daemon chdir(\"/\") failed");
 			return -1;