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_basebackup/bbstreamer_file.c b/src/bin/pg_basebackup/bbstreamer_file.c
index 2da7d33b4891262e280a36997b15b2962cf9ac35..0ffe5f5389a1fa70a96c9b57bc3e3c7c4f4b0d37 100644 (file)
--- a/src/bin/pg_basebackup/bbstreamer_file.c
+++ b/src/bin/pg_basebackup/bbstreamer_file.c
@@ -215,6 +215,10 @@ bbstreamer_extractor_content(bbstreamer *streamer, bbstreamer_member *member,
                case BBSTREAMER_MEMBER_HEADER:
                        Assert(mystreamer->file == NULL);
 
+                       if (!path_is_safe_for_extraction(member->pathname))
+                               pg_fatal("tar member has unsafe path name: \"%s\"",
+                                                member->pathname);
+
                        /* Prepend basepath. */
                        snprintf(mystreamer->filename, sizeof(mystreamer->filename),
                                         "%s/%s", mystreamer->basepath, member->pathname);
@@ -233,6 +237,14 @@ bbstreamer_extractor_content(bbstreamer *streamer, bbstreamer_member *member,
 
                                if (mystreamer->link_map)
                                        linktarget = mystreamer->link_map(linktarget);
+
+                               if (!is_absolute_path(linktarget) &&
+                                       !path_is_safe_for_extraction(member->linktarget))
+                               {
+                                       pg_fatal("link target has unsafe path name: \"%s\"",
+                                                        member->linktarget);
+                               }
+
                                extract_link(mystreamer->filename, linktarget);
                        }
                        else

diff --git a/src/bin/pg_basebackup/bbstreamer_tar.c b/src/bin/pg_basebackup/bbstreamer_tar.c
index d751ae91ea7436cd776d6f8a875339bfaae17213..18d934f4a4cb317068e8f0f7ba03fafc3f60bc0f 100644 (file)
--- a/src/bin/pg_basebackup/bbstreamer_tar.c
+++ b/src/bin/pg_basebackup/bbstreamer_tar.c
@@ -295,6 +295,9 @@ bbstreamer_tar_header(bbstreamer_tar_parser *mystreamer)
        strlcpy(member->pathname, &buffer[0], MAXPGPATH);
        if (member->pathname[0] == '\0')
                pg_fatal("tar member has empty name");
+       if (!path_is_safe_for_extraction(member->pathname))
+               pg_fatal("tar member has unsafe path name: \"%s\"",
+                                member->pathname);
        member->size = read_tar_number(&buffer[124], 12);
        member->mode = read_tar_number(&buffer[100], 8);
        member->uid = read_tar_number(&buffer[108], 8);

diff --git a/src/bin/pg_rewind/file_ops.c b/src/bin/pg_rewind/file_ops.c
index 745435060cce02731ed8d49ca382c09a8db750f4..25f2fc15b32231b5dda835836f55e80e537eda38 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 3e277d7e308ec371f91efdab954dc0685cb78d21..d869bff2bcef3b742c768b3e2afaf8dd0c5a8a28 100644 (file)
--- a/src/include/port.h
+++ b/src/include/port.h
@@ -58,6 +58,7 @@ extern void make_native_path(char *filename);
 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 817f6b08348b3edfb37bcfa6a8aaa87ec292373b..58732b134180c79fe6feded5a7d815afee10fdac 100644 (file)
--- a/src/port/path.c
+++ b/src/port/path.c
@@ -626,6 +626,23 @@ 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).
  *