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https://github.com/RsyncProject/rsync.git
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syscall: use openat2(RESOLVE_BENEATH) on Linux for secure_relative_open
The CVE fix in commit c35e283 made secure_relative_open() walk every
component of relpath with O_NOFOLLOW. That blocks every symlink in the
path, which is stricter than the threat model required: legitimate
directory symlinks within the destination tree (e.g. when using -K /
--copy-dirlinks) are also rejected, breaking delta transfers with
"failed verification -- update discarded". See issue #715.
On Linux 5.6+, openat2(RESOLVE_BENEATH | RESOLVE_NO_MAGICLINKS) gives
us exactly what we want: the kernel rejects any resolution that would
escape the starting directory (via "..", absolute paths, or symlinks
pointing outside dirfd) while still following symlinks that resolve
within it. /proc magic-links are blocked too.
Use openat2 first; fall back to the existing per-component O_NOFOLLOW
walk on ENOSYS (kernel < 5.6). The lexical "../" checks at the head
of the function are kept as defense in depth. The Linux gate is
plain #ifdef __linux__: the runtime ENOSYS fallback covers the only
case that actually matters (header present + old kernel), and any
Linux build environment without linux/openat2.h will fail with a
clear "no such file" error rather than silently disabling the
protection.
Verified manually that openat2(RESOLVE_BENEATH) blocks all four
escape patterns (absolute symlink, ../ symlink, lexical .., absolute
path) while allowing direct and within-tree symlinks. The new
testsuite/symlink-dirlink-basis.test (taken from PR #864 by Samuel
Henrique) exercises the issue #715 regression and passes; full
make check passes 47/47.
Test: testsuite/symlink-dirlink-basis.test (8 scenarios)
Fixes: https://github.com/RsyncProject/rsync/issues/715
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
This commit is contained in:
Andrew Tridgell
60
syscall.c
60
syscall.c
@@ -33,6 +33,11 @@
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#include <sys/syscall.h>
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#endif
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#ifdef __linux__
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#include <sys/syscall.h>
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#include <linux/openat2.h>
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#endif
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#include "ifuncs.h"
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extern int dry_run;
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@@ -720,12 +725,49 @@ int do_open_nofollow(const char *pathname, int flags)
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/*
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open a file relative to a base directory. The basedir can be NULL,
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in which case the current working directory is used. The relpath
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must be a relative path, and the relpath must not contain any
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elements in the path which follow symlinks (ie. like O_NOFOLLOW, but
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applies to all path components, not just the last component)
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must be a relative path. The kernel must guarantee that resolution
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cannot escape basedir (or the cwd, when basedir is NULL): no ".."
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jumps above the start, no symlinks pointing outside, no absolute
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paths, no /proc magic-link tricks.
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The relpath must also not contain any ../ elements in the path
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Symlinks *within* basedir are followed normally — earlier rsync
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versions rejected every symlink with O_NOFOLLOW on each component,
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which broke legitimate directory symlinks on the receiver side
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(https://github.com/RsyncProject/rsync/issues/715). The escape
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prevention is handled by the kernel via openat2(RESOLVE_BENEATH)
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on Linux 5.6+; older systems fall back to the per-component
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O_NOFOLLOW walk below.
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The relpath must also not contain any ../ elements in the path.
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*/
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#ifdef __linux__
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static int secure_relative_open_linux(const char *basedir, const char *relpath, int flags, mode_t mode)
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{
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struct open_how how;
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int dirfd, retfd;
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memset(&how, 0, sizeof how);
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how.flags = flags;
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how.mode = mode;
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how.resolve = RESOLVE_BENEATH | RESOLVE_NO_MAGICLINKS;
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if (basedir == NULL) {
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dirfd = AT_FDCWD;
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} else {
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dirfd = openat(AT_FDCWD, basedir, O_RDONLY | O_DIRECTORY);
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if (dirfd == -1)
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return -1;
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}
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retfd = syscall(SYS_openat2, dirfd, relpath, &how, sizeof how);
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if (dirfd != AT_FDCWD)
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close(dirfd);
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return retfd;
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}
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#endif
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int secure_relative_open(const char *basedir, const char *relpath, int flags, mode_t mode)
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{
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if (!relpath || relpath[0] == '/') {
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@@ -739,6 +781,16 @@ int secure_relative_open(const char *basedir, const char *relpath, int flags, mo
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return -1;
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}
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#ifdef __linux__
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{
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int fd = secure_relative_open_linux(basedir, relpath, flags, mode);
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/* ENOSYS = kernel < 5.6 doesn't have the syscall even though
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* glibc/kernel-headers do; fall through to the portable path. */
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if (fd != -1 || errno != ENOSYS)
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return fd;
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}
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#endif
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#if !defined(O_NOFOLLOW) || !defined(O_DIRECTORY) || !defined(AT_FDCWD)
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// really old system, all we can do is live with the risks
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if (!basedir) {
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247
testsuite/symlink-dirlink-basis.test
Executable file
247
testsuite/symlink-dirlink-basis.test
Executable file
@@ -0,0 +1,247 @@
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#!/bin/sh
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# Test that updating a file through a directory symlink works when using
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# -K (--copy-dirlinks). This is a regression test for:
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# https://github.com/RsyncProject/rsync/issues/715
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#
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# The CVE fix in commit c35e283 introduced secure_relative_open() which
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# uses O_NOFOLLOW on all path components, breaking legitimate directory
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# symlinks on the receiver side. The fix splits the path into basedir
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# (dirname, symlinks followed) and basename (O_NOFOLLOW) so that
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# directory symlinks are traversed while the final file component is
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# still protected.
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#
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# The regression only manifests when delta matching is triggered (i.e.,
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# the sender finds matching blocks in the old file). Small files with
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# completely different content are transferred in full and don't trigger
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# the bug. We use a large file with a small modification to ensure
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# delta transfer is used.
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#
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# In addition to the original regression, this test covers edge cases
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# in the fix itself:
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# - --backup with directory symlinks (finish_transfer pointer identity)
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# - --partial-dir with protocol < 29 (fnamecmp != partialptr guard)
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# - --inplace with directory symlinks (updating_basis_or_equiv check)
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# - Files without a dirname (top-level files, no split needed)
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. "$suitedir/rsync.fns"
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RSYNC_RSH="$scratchdir/src/support/lsh.sh"
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export RSYNC_RSH
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# $HOME is set to $scratchdir by rsync.fns
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# localhost: destination will cd to $HOME (i.e., $scratchdir)
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# Helper: create a large file suitable for delta transfers.
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# ~32KB is large enough for rsync's block matching to find matches.
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make_testfile() {
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dd if=/dev/urandom of="$1" bs=1024 count=32 2>/dev/null \
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|| test_fail "failed to create test file $1"
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}
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# Set up source tree
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srcbase="$tmpdir/src"
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######################################################################
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# Test 1: Basic directory symlink update (the original issue #715)
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######################################################################
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mkdir -p "$HOME/real-dir"
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ln -s real-dir "$HOME/dir"
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mkdir -p "$srcbase/dir"
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make_testfile "$srcbase/dir/file"
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# First transfer (initial): should create the file through the symlink
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(cd "$srcbase" && $RSYNC -KRlptv --rsync-path="$RSYNC" dir/file localhost:) \
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|| test_fail "test 1: initial transfer failed"
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if [ ! -f "$HOME/real-dir/file" ]; then
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test_fail "test 1: initial transfer did not create file through symlink"
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fi
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diff "$srcbase/dir/file" "$HOME/real-dir/file" >/dev/null \
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|| test_fail "test 1: initial transfer content mismatch"
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# Small modification to trigger delta transfer
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echo "appended update" >> "$srcbase/dir/file"
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sleep 1
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touch "$srcbase/dir/file"
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# Second transfer (update): was failing with "failed verification"
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(cd "$srcbase" && $RSYNC -KRlptv --rsync-path="$RSYNC" dir/file localhost:) \
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|| test_fail "test 1: update through directory symlink failed"
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diff "$srcbase/dir/file" "$HOME/real-dir/file" >/dev/null \
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|| test_fail "test 1: update transfer content mismatch"
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######################################################################
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# Test 2: Compression (-z) as in the original reproducer
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######################################################################
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echo "another line" >> "$srcbase/dir/file"
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sleep 1
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touch "$srcbase/dir/file"
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(cd "$srcbase" && $RSYNC -KRlptzv --rsync-path="$RSYNC" dir/file localhost:) \
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|| test_fail "test 2: compressed update through directory symlink failed"
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diff "$srcbase/dir/file" "$HOME/real-dir/file" >/dev/null \
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|| test_fail "test 2: compressed update content mismatch"
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######################################################################
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# Test 3: Nested directory symlinks (nested/sub/data.txt where
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# "nested" is a symlink to "nested_real")
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######################################################################
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mkdir -p "$HOME/nested_real/sub"
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ln -s nested_real "$HOME/nested"
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mkdir -p "$srcbase/nested/sub"
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make_testfile "$srcbase/nested/sub/data.txt"
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(cd "$srcbase" && $RSYNC -KRlptv --rsync-path="$RSYNC" nested/sub/data.txt localhost:) \
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|| test_fail "test 3: initial nested transfer failed"
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echo "appended nested" >> "$srcbase/nested/sub/data.txt"
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sleep 1
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touch "$srcbase/nested/sub/data.txt"
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(cd "$srcbase" && $RSYNC -KRlptv --rsync-path="$RSYNC" nested/sub/data.txt localhost:) \
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|| test_fail "test 3: update through nested directory symlink failed"
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diff "$srcbase/nested/sub/data.txt" "$HOME/nested_real/sub/data.txt" >/dev/null \
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|| test_fail "test 3: nested update content mismatch"
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######################################################################
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# Test 4: --backup with directory symlinks
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#
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# Exercises the finish_transfer() "fnamecmp == fname" pointer
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# comparison that determines whether to update fnamecmp to the
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# backup name. If broken, --backup would reference a renamed file
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# for xattr handling.
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######################################################################
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# Reset destination
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rm -f "$HOME/real-dir/file" "$HOME/real-dir/file~"
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make_testfile "$srcbase/dir/file"
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(cd "$srcbase" && $RSYNC -KRlptv --rsync-path="$RSYNC" dir/file localhost:) \
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|| test_fail "test 4: initial transfer for backup test failed"
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echo "backup update" >> "$srcbase/dir/file"
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sleep 1
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touch "$srcbase/dir/file"
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(cd "$srcbase" && $RSYNC -KRlptv --backup --rsync-path="$RSYNC" dir/file localhost:) \
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|| test_fail "test 4: update with --backup through directory symlink failed"
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diff "$srcbase/dir/file" "$HOME/real-dir/file" >/dev/null \
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|| test_fail "test 4: backup update content mismatch"
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if [ ! -f "$HOME/real-dir/file~" ]; then
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test_fail "test 4: backup file was not created"
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fi
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######################################################################
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# Test 5: --inplace with directory symlinks
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#
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# Exercises the updating_basis_or_equiv check which uses
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# "fnamecmp == fname". With --inplace, rsync writes directly to
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# the destination file instead of a temp file.
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######################################################################
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rm -f "$HOME/real-dir/file" "$HOME/real-dir/file~"
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make_testfile "$srcbase/dir/file"
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(cd "$srcbase" && $RSYNC -KRlptv --inplace --rsync-path="$RSYNC" dir/file localhost:) \
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|| test_fail "test 5: initial inplace transfer failed"
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echo "inplace update" >> "$srcbase/dir/file"
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sleep 1
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touch "$srcbase/dir/file"
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(cd "$srcbase" && $RSYNC -KRlptv --inplace --rsync-path="$RSYNC" dir/file localhost:) \
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|| test_fail "test 5: inplace update through directory symlink failed"
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diff "$srcbase/dir/file" "$HOME/real-dir/file" >/dev/null \
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|| test_fail "test 5: inplace update content mismatch"
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######################################################################
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# Test 6: Top-level file (no dirname, no split needed)
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#
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# Ensures the dirname/basename split is not attempted for files
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# at the top level (file->dirname is NULL).
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######################################################################
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make_testfile "$srcbase/topfile"
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mkdir -p "$HOME"
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(cd "$srcbase" && $RSYNC -Rlptv --rsync-path="$RSYNC" topfile localhost:) \
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|| test_fail "test 6: initial top-level transfer failed"
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echo "toplevel update" >> "$srcbase/topfile"
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sleep 1
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touch "$srcbase/topfile"
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(cd "$srcbase" && $RSYNC -Rlptv --rsync-path="$RSYNC" topfile localhost:) \
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|| test_fail "test 6: top-level update failed"
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diff "$srcbase/topfile" "$HOME/topfile" >/dev/null \
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|| test_fail "test 6: top-level update content mismatch"
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######################################################################
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# Test 7: --partial-dir with protocol < 29
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#
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# For protocol < 29, fnamecmp_type stays FNAMECMP_FNAME even when
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# fnamecmp is set to partialptr. The dirname/basename split must
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# NOT trigger in this case (guarded by "fnamecmp == fname").
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######################################################################
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rm -f "$HOME/real-dir/file"
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make_testfile "$srcbase/dir/file"
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(cd "$srcbase" && $RSYNC -KRlptv --protocol=28 --partial-dir=.rsync-partial \
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--rsync-path="$RSYNC" dir/file localhost:) \
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|| test_fail "test 7: initial proto28 partial-dir transfer failed"
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echo "partial-dir update" >> "$srcbase/dir/file"
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sleep 1
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touch "$srcbase/dir/file"
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(cd "$srcbase" && $RSYNC -KRlptv --protocol=28 --partial-dir=.rsync-partial \
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--rsync-path="$RSYNC" dir/file localhost:) \
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|| test_fail "test 7: proto28 partial-dir update through dirlink failed"
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diff "$srcbase/dir/file" "$HOME/real-dir/file" >/dev/null \
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|| test_fail "test 7: proto28 partial-dir update content mismatch"
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######################################################################
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# Test 8: Protocol < 29 basic directory symlink update
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#
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# Exercises the protocol < 29 code path and its fallback logic
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# (clearing basedir on retry).
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######################################################################
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rm -f "$HOME/real-dir/file"
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make_testfile "$srcbase/dir/file"
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(cd "$srcbase" && $RSYNC -KRlptv --protocol=28 \
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--rsync-path="$RSYNC" dir/file localhost:) \
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|| test_fail "test 8: initial proto28 transfer failed"
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echo "proto28 update" >> "$srcbase/dir/file"
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sleep 1
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touch "$srcbase/dir/file"
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(cd "$srcbase" && $RSYNC -KRlptv --protocol=28 \
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--rsync-path="$RSYNC" dir/file localhost:) \
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|| test_fail "test 8: proto28 update through directory symlink failed"
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diff "$srcbase/dir/file" "$HOME/real-dir/file" >/dev/null \
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|| test_fail "test 8: proto28 update content mismatch"
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# The script would have aborted on error, so getting here means we've won.
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exit 0
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