Prevent path traversal in pg_basebackup and pg_rewind

pg_rewind and pg_basebackup could be fed paths from rogue endpoints that
could overwrite the contents of the client when received, achieving path
traversal.

There were two areas in the tree that were sensitive to this problem:
- pg_basebackup, through the astreamer code, where no validation was
performed before building an output path when streaming tar data.  This
is an issue in v15 and newer versions.
- pg_rewind file operations for paths received through libpq, for all
the stable branches supported.

In order to address this problem, this commit adds a helper function in
path.c, that reuses path_is_relative_and_below_cwd() after applying
canonicalize_path().  This can be used to validate the paths received
from a connection point.  A path is considered invalid if any of the two
following conditions is satisfied:
- The path is absolute.
- The path includes a direct parent-directory reference.

Reported-by: XlabAI Team of Tencent Xuanwu Lab
Reported-by: Valery Gubanov <valerygubanov95@gmail.com>
Author: Michael Paquier <michael@paquier.xyz>
Reviewed-by: Amit Kapila <amit.kapila16@gmail.com>
Backpatch-through: 14
Security: CVE-2026-6475

diff --git a/src/bin/pg_rewind/file_ops.c b/src/bin/pg_rewind/file_ops.c
index a8070864bbe95519cb51adea9b9d934f41bd8f5c..faaa5cebdf3275fe6248ae3e7396809c9addb1a2 100644 (file)
--- a/src/bin/pg_rewind/file_ops.c
+++ b/src/bin/pg_rewind/file_ops.c
@@ -48,6 +48,9 @@ open_target_file(const char *path, bool trunc)
 {
        int                     mode;
 
+       if (!path_is_safe_for_extraction(path))
+               pg_fatal("target file path is unsafe for open: \"%s\"", path);
+
        if (dry_run)
                return;
 
@@ -188,6 +191,9 @@ remove_target_file(const char *path, bool missing_ok)
 {
        char            dstpath[MAXPGPATH];
 
+       if (!path_is_safe_for_extraction(path))
+               pg_fatal("target file path is unsafe for removal: \"%s\"", path);
+
        if (dry_run)
                return;
 
@@ -208,6 +214,9 @@ truncate_target_file(const char *path, off_t newsize)
        char            dstpath[MAXPGPATH];
        int                     fd;
 
+       if (!path_is_safe_for_extraction(path))
+               pg_fatal("target file path is unsafe for truncation: \"%s\"", path);
+
        if (dry_run)
                return;
 
@@ -230,6 +239,10 @@ create_target_dir(const char *path)
 {
        char            dstpath[MAXPGPATH];
 
+       if (!path_is_safe_for_extraction(path))
+               pg_fatal("target directory path is unsafe for directory creation: \"%s\"",
+                                path);
+
        if (dry_run)
                return;
 
@@ -244,6 +257,10 @@ remove_target_dir(const char *path)
 {
        char            dstpath[MAXPGPATH];
 
+       if (!path_is_safe_for_extraction(path))
+               pg_fatal("target directory path is unsafe for directory removal: \"%s\"",
+                                path);
+
        if (dry_run)
                return;
 
@@ -258,6 +275,9 @@ create_target_symlink(const char *path, const char *link)
 {
        char            dstpath[MAXPGPATH];
 
+       if (!path_is_safe_for_extraction(path))
+               pg_fatal("target symlink path is unsafe for creation: \"%s\"", path);
+
        if (dry_run)
                return;
 
@@ -272,6 +292,9 @@ remove_target_symlink(const char *path)
 {
        char            dstpath[MAXPGPATH];
 
+       if (!path_is_safe_for_extraction(path))
+               pg_fatal("target symlink path is unsafe for removal: \"%s\"", path);
+
        if (dry_run)
                return;
 

diff --git a/src/include/port.h b/src/include/port.h
index db53decbbef73a3da15bfd7f2259afc233ee326c..a257d8d3a01a29fcff71162c916cb8cafcf1bfff 100644 (file)
--- a/src/include/port.h
+++ b/src/include/port.h
@@ -55,6 +55,7 @@ extern void make_native_path(char *path);
 extern void cleanup_path(char *path);
 extern bool path_contains_parent_reference(const char *path);
 extern bool path_is_relative_and_below_cwd(const char *path);
+extern bool path_is_safe_for_extraction(const char *path);
 extern bool path_is_prefix_of_path(const char *path1, const char *path2);
 extern char *make_absolute_path(const char *path);
 extern const char *get_progname(const char *argv0);

diff --git a/src/port/path.c b/src/port/path.c
index d37a484c8654fb00452bd17604a687ae75fab268..117f9199c11600e2e23800f17a5d3d14c2f81b3f 100644 (file)
--- a/src/port/path.c
+++ b/src/port/path.c
@@ -505,6 +505,23 @@ path_is_relative_and_below_cwd(const char *path)
                return true;
 }
 
+/*
+ * Detect whether a path is safe for use during archive extraction.
+ *
+ * This applies canonicalize_path(), then it checks that the path does
+ * not contain any parent directory references.
+ */
+bool
+path_is_safe_for_extraction(const char *path)
+{
+       char            buf[MAXPGPATH];
+
+       strlcpy(buf, path, sizeof(buf));
+       canonicalize_path(buf);
+
+       return path_is_relative_and_below_cwd(buf);
+}
+
 /*
  * Detect whether path1 is a prefix of path2 (including equality).
  *