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 5cfb676f41f872d1ed6cd97229f382c0e42ce2da..acd8fa758fda2bf1ec815b0a37dd036118575e8f 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/fe_utils/astreamer_file.c b/src/fe_utils/astreamer_file.c
index 0fca70a4f867dcd8d21a4c70b1627ca1dd2a2d3c..fb36cecc22a38f005b9f0d5036b65180cfbeaae4 100644 (file)
--- a/src/fe_utils/astreamer_file.c
+++ b/src/fe_utils/astreamer_file.c
@@ -218,6 +218,10 @@ astreamer_extractor_content(astreamer *streamer, astreamer_member *member,
                case ASTREAMER_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);
@@ -240,6 +244,14 @@ astreamer_extractor_content(astreamer *streamer, astreamer_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);
                        }
 

diff --git a/src/fe_utils/astreamer_tar.c b/src/fe_utils/astreamer_tar.c
index f584665057dabfdbd22dc4588be61c3ea8929eef..8ab59e92238197f5e8eaa14ac2f8ff5e28500cb1 100644 (file)
--- a/src/fe_utils/astreamer_tar.c
+++ b/src/fe_utils/astreamer_tar.c
@@ -305,6 +305,10 @@ astreamer_tar_header(astreamer_tar_parser *mystreamer)
        strlcpy(member->pathname, &buffer[TAR_OFFSET_NAME], 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[TAR_OFFSET_SIZE], 12);
        member->mode = read_tar_number(&buffer[TAR_OFFSET_MODE], 8);
        member->uid = read_tar_number(&buffer[TAR_OFFSET_UID], 8);

diff --git a/src/include/port.h b/src/include/port.h
index c029878c6beeb264f9377c9ae8115036ddca9cfc..d3924ece96cffcb2dd9410a2753afacec94938cd 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 2395b96fd3b98f6f5f88c2d88c3df1e7aa022501..fef0ae77f87a8b4bcdec5fdc360ffff2ed0bd3d5 100644 (file)
--- a/src/port/path.c
+++ b/src/port/path.c
@@ -627,6 +627,23 @@ 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).
  *