rpm/0004-Report-unsafe-symlinks-during-installation-as-a-spec.patch

From 1e6cdb256c06b084501f5016d10bb5c8465c8287 Mon Sep 17 00:00:00 2001
From: Panu Matilainen <pmatilai@redhat.com>
Date: Mon, 19 Aug 2024 11:03:10 +0300
Subject: [PATCH 4/5] Report unsafe symlinks during installation as a specific
 case

RPM refuses to follow non root owned symlinks pointing to files owned by
another user for security reasons. This case was lumped in with
O_DIRECTORY behavior, leading to confusing error message as the symlink
often indeed points at a directory. Emit a more meaningful error message
when encountering unsafe symlinks.

We already detect the error condition in the main if block here, might
as well set the error code right there and then so we don't need to
redetect later. We previously only tested for the unsafe link condition
when our O_DIRECTORY equivalent was set, but that seems wrong. Probably
doesn't matter with the existing callers, but we really must not
follow those unsafe symlinks no matter what.

Co-authored-by: Florian Festi <ffesti@redhat.com>

Backported from commits:
14516542c113560dc0070df2f9102568a7a71b58
535eacc96ae6fe5289a2917bb0af43e491b0f4f4

Tests are excluded from this backport since they would need significant
rework, the use case will be covered by Beaker.

Fixes: RHEL-39897
---
 lib/fsm.c   | 70 +++++++++++++++++++++++++++--------------------------
 lib/rpmfi.c |  1 +
 2 files changed, 37 insertions(+), 34 deletions(-)

diff --git a/lib/fsm.c b/lib/fsm.c
index 9dd50b784..720d4a2ec 100644
--- a/lib/fsm.c
+++ b/lib/fsm.c
@@ -65,7 +65,7 @@ struct filedata_s {
  * things around needlessly 
  */ 
 static const char * fileActionString(rpmFileAction a);
-static int fsmOpenat(int dirfd, const char *path, int flags, int dir);
+static int fsmOpenat(int *fdp, int dirfd, const char *path, int flags, int dir);
 static int fsmClose(int *wfdp);
 
 /** \ingroup payload
@@ -98,9 +98,9 @@ static int fsmLink(int odirfd, const char *opath, int dirfd, const char *path)
 #ifdef WITH_CAP
 static int cap_set_fileat(int dirfd, const char *path, cap_t fcaps)
 {
-    int rc = -1;
-    int fd = fsmOpenat(dirfd, path, O_RDONLY|O_NOFOLLOW, 0);
-    if (fd >= 0) {
+    int fd = -1;
+    int rc = fsmOpenat(&fd, dirfd, path, O_RDONLY|O_NOFOLLOW, 0);
+    if (!rc) {
 	rc = cap_set_fd(fd, fcaps);
 	fsmClose(&fd);
     }
@@ -299,12 +299,12 @@ static int fsmMkdir(int dirfd, const char *path, mode_t mode)
     return rc;
 }
 
-static int fsmOpenat(int dirfd, const char *path, int flags, int dir)
+static int fsmOpenat(int *wfdp, int dirfd, const char *path, int flags, int dir)
 {
     struct stat lsb, sb;
     int sflags = flags | O_NOFOLLOW;
     int fd = openat(dirfd, path, sflags);
-    int ffd = fd;
+    int rc = 0;
 
     /*
      * Only ever follow symlinks by root or target owner. Since we can't
@@ -313,7 +313,7 @@ static int fsmOpenat(int dirfd, const char *path, int flags, int dir)
      * it could've only been the link owner or root.
      */
     if (fd < 0 && errno == ELOOP && flags != sflags) {
-	ffd = openat(dirfd, path, flags);
+	int ffd = openat(dirfd, path, flags);
 	if (ffd >= 0) {
 	    if (fstatat(dirfd, path, &lsb, AT_SYMLINK_NOFOLLOW) == 0) {
 		if (fstat(ffd, &sb) == 0) {
@@ -322,17 +322,26 @@ static int fsmOpenat(int dirfd, const char *path, int flags, int dir)
 		    }
 		}
 	    }
-	    if (ffd != fd)
+	    /* Symlink with non-matching owners */
+	    if (ffd != fd) {
 		close(ffd);
+		rc = RPMERR_INVALID_SYMLINK;
+	    }
 	}
     }
 
     /* O_DIRECTORY equivalent */
-    if (dir && ((fd != ffd) || (fd >= 0 && fstat(fd, &sb) == 0 && !S_ISDIR(sb.st_mode)))) {
-	errno = ENOTDIR;
+    if (!rc && dir && fd >= 0 && fstat(fd, &sb) == 0 && !S_ISDIR(sb.st_mode))
+	rc = RPMERR_ENOTDIR;
+
+    if (!rc && fd < 0)
+	rc = RPMERR_OPEN_FAILED;
+
+    if (rc)
 	fsmClose(&fd);
-    }
-    return fd;
+
+    *wfdp = fd;
+    return rc;
 }
 
 static int fsmDoMkDir(rpmPlugins plugins, int dirfd, const char *dn,
@@ -351,9 +360,7 @@ static int fsmDoMkDir(rpmPlugins plugins, int dirfd, const char *dn,
 	rc = fsmMkdir(dirfd, dn, mode);
 
     if (!rc) {
-	*fdp = fsmOpenat(dirfd, dn, O_RDONLY|O_NOFOLLOW, 1);
-	if (*fdp == -1)
-	    rc = RPMERR_ENOTDIR;
+	rc = fsmOpenat(fdp, dirfd, dn, O_RDONLY|O_NOFOLLOW, 1);
     }
 
     if (!rc) {
@@ -378,47 +385,44 @@ static int ensureDir(rpmPlugins plugins, const char *p, int owned, int create,
     char *sp = NULL, *bn;
     char *apath = NULL;
     int oflags = O_RDONLY;
-    int rc = 0;
 
     if (*dirfdp >= 0)
-	return rc;
+	return 0;
 
-    int dirfd = fsmOpenat(-1, "/", oflags, 1);
+    int dirfd = -1;
+    int rc = fsmOpenat(&dirfd, -1, "/", oflags, 1);
     int fd = dirfd; /* special case of "/" */
 
     char *path = xstrdup(p);
     char *dp = path;
 
     while ((bn = strtok_r(dp, "/", &sp)) != NULL) {
-	fd = fsmOpenat(dirfd, bn, oflags, 1);
+	rc = fsmOpenat(&fd, dirfd, bn, oflags, 1);
 	/* assemble absolute path for plugins benefit, sigh */
 	apath = rstrscat(&apath, "/", bn, NULL);
 
-	if (fd < 0 && errno == ENOENT && create) {
+	if (rc && errno == ENOENT && create) {
 	    mode_t mode = S_IFDIR | (_dirPerms & 07777);
 	    rc = fsmDoMkDir(plugins, dirfd, bn, apath, owned, mode, &fd);
 	}
 
 	fsmClose(&dirfd);
-	if (fd >= 0) {
-	    dirfd = fd;
-	} else {
-	    if (!quiet) {
-		rpmlog(RPMLOG_ERR, _("failed to open dir %s of %s: %s\n"),
-			bn, p, strerror(errno));
-	    }
-	    rc = RPMERR_OPEN_FAILED;
+	if (rc)
 	    break;
-	}
 
+	dirfd = fd;
 	dp = NULL;
     }
 
     if (rc) {
+	if (!quiet) {
+	    char *msg = rpmfileStrerror(rc);
+	    rpmlog(RPMLOG_ERR, _("failed to open dir %s of %s: %s\n"),
+		    bn, p, msg);
+	    free(msg);
+	}
 	fsmClose(&fd);
 	fsmClose(&dirfd);
-    } else {
-	rc = 0;
     }
     *dirfdp = dirfd;
 
@@ -1025,10 +1029,8 @@ setmeta:
 		/* Only follow safe symlinks, and never on temporary files */
 		if (fp->suffix)
 		    flags |= AT_SYMLINK_NOFOLLOW;
-		fd = fsmOpenat(di.dirfd, fp->fpath, flags,
+		rc = fsmOpenat(&fd, di.dirfd, fp->fpath, flags,
 				S_ISDIR(fp->sb.st_mode));
-		if (fd < 0)
-		    rc = RPMERR_OPEN_FAILED;
 	    }
 
 	    if (!rc && fp->setmeta) {
diff --git a/lib/rpmfi.c b/lib/rpmfi.c
index 0aacd9f85..821bae875 100644
--- a/lib/rpmfi.c
+++ b/lib/rpmfi.c
@@ -2432,6 +2432,7 @@ char * rpmfileStrerror(int rc)
     case RPMERR_DIGEST_MISMATCH: s = _("Digest mismatch");	break;
     case RPMERR_INTERNAL:	s = _("Internal error");	break;
     case RPMERR_UNMAPPED_FILE:	s = _("Archive file not in header"); break;
+    case RPMERR_INVALID_SYMLINK: s = _("Unsafe symlink");	break;
     case RPMERR_ENOENT:	s = strerror(ENOENT); break;
     case RPMERR_ENOTEMPTY:	s = strerror(ENOTEMPTY); break;
     case RPMERR_EXIST_AS_DIR:
-- 
2.47.0