elf: Restore ldconfig libc6 implicit soname logic [BZ #30125]

While cleaning up old libc version support, the deprecated libc4 code was
accidentally kept in `implicit_soname`, instead of the libc6 code.

This causes additional symlinks to be created by `ldconfig` for libraries
without a soname, e.g. a library `libsomething.123.456.789` without a soname
will create a `libsomething.123` -> `libsomething.123.456.789` symlink.

As the libc6 version of the `implicit_soname` code is a trivial `xstrdup`,
just inline it and remove `implicit_soname` altogether.

Some further simplification looks possible (e.g. the call to `create_links`
looks like a no-op if `soname == NULL`, other than the verbose printfs), but
logic is kept as-is for now.

Fixes: BZ #30125
Fixes: 8ee878592c4a ("Assume only FLAG_ELF_LIBC6 suport")
Signed-off-by: Joan Bruguera <joanbrugueram@gmail.com>

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>
(cherry picked from commit 1b0ea8c5d886fedabd611a569b5ec58a6f5153e6)

8 files changed, 69 insertions, 23 deletions

diff --git a/NEWS b/NEWS
index 7ba8846fcc..e1562857b1 100644
--- a/NEWS
+++ b/NEWS
@@ -19,6 +19,8 @@ Security related changes:
 The following bugs are resolved with this release:
 
   [30053] time: strftime %s returns -1 after 2038 on 32 bits systems
+  [30125] dynamic-link: [regression, bisected] glibc-2.37 creates new
+    symlink for libraries without soname
 
 Version 2.37
 
diff --git a/elf/Makefile b/elf/Makefile
index 2fc6391183..0d19964d42 100644
--- a/elf/Makefile
+++ b/elf/Makefile
@@ -627,6 +627,7 @@ tests-special += \
   $(objpfx)noload-mem.out \
   $(objpfx)tst-ldconfig-X.out \
   $(objpfx)tst-ldconfig-p.out \
+  $(objpfx)tst-ldconfig-soname.out \
   $(objpfx)tst-leaks1-mem.out \
   $(objpfx)tst-rtld-help.out \
   # tests-special
@@ -859,6 +860,8 @@ modules-names += \
   tst-initorderb2 \
   tst-latepthreadmod \
   tst-ldconfig-ld-mod \
+  tst-ldconfig-soname-lib-with-soname \
+  tst-ldconfig-soname-lib-without-soname \
   tst-main1mod \
   tst-nodelete2mod \
   tst-nodelete-dlclose-dso \
@@ -2402,6 +2405,17 @@ $(objpfx)tst-ldconfig-p.out : tst-ldconfig-p.sh $(objpfx)ldconfig
 		 '$(run-program-env)' > $@; \
 	$(evaluate-test)
 
+LDFLAGS-tst-ldconfig-soname-lib-with-soname.so = \
+  -Wl,-soname,libtst-ldconfig-soname-lib-with-soname.so.1
+
+$(objpfx)tst-ldconfig-soname.out : tst-ldconfig-soname.sh \
+  $(objpfx)ldconfig \
+  $(objpfx)tst-ldconfig-soname-lib-with-soname.so \
+  $(objpfx)tst-ldconfig-soname-lib-without-soname.so
+	$(SHELL) $< '$(common-objpfx)' '$(test-wrapper-env)' \
+		 '$(run-program-env)' > $@; \
+	$(evaluate-test)
+
 # Test static linking of all the libraries we can possibly link
 # together.  Note that in some configurations this may be less than the
 # complete list of libraries we build but we try to maxmimize this list.
diff --git a/elf/ldconfig.c b/elf/ldconfig.c
index 166dccb528..5b1c9139f6 100644
--- a/elf/ldconfig.c
+++ b/elf/ldconfig.c
@@ -616,7 +616,7 @@ manual_link (char *library)
       goto out;
     }
   if (soname == NULL)
-    soname = implicit_soname (libname, flag);
+    soname = xstrdup (libname);
   create_links (real_path, path, libname, soname);
   free (soname);
 out:
@@ -849,7 +849,7 @@ search_dir (const struct dir_entry *entry)
 	}
 
       if (soname == NULL)
-	soname = implicit_soname (direntry->d_name, flag);
+	soname = xstrdup (direntry->d_name);
 
       /* A link may just point to itself.  */
       if (is_link)
diff --git a/elf/readlib.c b/elf/readlib.c
index c5c3591eef..bc13d9acc6 100644
--- a/elf/readlib.c
+++ b/elf/readlib.c
@@ -166,24 +166,5 @@ process_file (const char *real_file_name, const char *file_name,
   return ret;
 }
 
-/* Returns made up soname if lib doesn't have explicit DT_SONAME.  */
-
-char *
-implicit_soname (const char *lib, int flag)
-{
-  char *soname = xstrdup (lib);
-
-  /* Aout files don't have a soname, just return the name
-     including the major number.  */
-  char *major = strstr (soname, ".so.");
-  if (major)
-    {
-      char *dot = strstr (major + 4, ".");
-      if (dot)
-	*dot = '\0';
-    }
-  return soname;
-}
-
 /* Get architecture specific version of process_elf_file.  */
 #include <readelflib.c>
diff --git a/elf/tst-ldconfig-soname-lib-with-soname.c b/elf/tst-ldconfig-soname-lib-with-soname.c
new file mode 100644
index 0000000000..d1ab56ad58
--- /dev/null
+++ b/elf/tst-ldconfig-soname-lib-with-soname.c
@@ -0,0 +1 @@
+/* This file intentionally left blank */
diff --git a/elf/tst-ldconfig-soname-lib-without-soname.c b/elf/tst-ldconfig-soname-lib-without-soname.c
new file mode 100644
index 0000000000..d1ab56ad58
--- /dev/null
+++ b/elf/tst-ldconfig-soname-lib-without-soname.c
@@ -0,0 +1 @@
+/* This file intentionally left blank */
diff --git a/elf/tst-ldconfig-soname.sh b/elf/tst-ldconfig-soname.sh
new file mode 100644
index 0000000000..406f526dbf
--- /dev/null
+++ b/elf/tst-ldconfig-soname.sh
@@ -0,0 +1,49 @@
+#!/bin/sh
+# Test that ldconfig creates symlinks according to the library's soname
+# (and in particular, does not create symlinks for libraries without a soname)
+# Copyright (C) 2000-2023 Free Software Foundation, Inc.
+# Copyright The GNU Toolchain Authors.
+# This file is part of the GNU C Library.
+
+# The GNU C Library is free software; you can redistribute it and/or
+# modify it under the terms of the GNU Lesser General Public
+# License as published by the Free Software Foundation; either
+# version 2.1 of the License, or (at your option) any later version.
+
+# The GNU C Library is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+# Lesser General Public License for more details.
+
+# You should have received a copy of the GNU Lesser General Public
+# License along with the GNU C Library; if not, see
+# <https://www.gnu.org/licenses/>.
+
+set -ex
+
+common_objpfx=$1
+test_wrapper_env=$2
+run_program_env=$3
+
+testroot="${common_objpfx}elf/bug30125-test-directory"
+cleanup () {
+    rm -rf "$testroot"
+}
+trap cleanup 0
+
+rm -rf "$testroot"
+mkdir -p $testroot/lib
+cp "${common_objpfx}elf/tst-ldconfig-soname-lib-with-soname.so" \
+    $testroot/lib/libtst-ldconfig-soname-lib-with-soname.so.1.2.3
+cp "${common_objpfx}elf/tst-ldconfig-soname-lib-without-soname.so" \
+    $testroot/lib/libtst-ldconfig-soname-lib-without-soname.so.1.2.3
+
+${test_wrapper_env} \
+${run_program_env} \
+${common_objpfx}elf/ldconfig -vn $testroot/lib
+
+LINKS=$(cd $testroot/lib && find . -type l)
+if [ "$LINKS" != "./libtst-ldconfig-soname-lib-with-soname.so.1" ]; then
+    echo "error: $0 - extra symlinks found"
+    exit 1
+fi
diff --git a/sysdeps/generic/ldconfig.h b/sysdeps/generic/ldconfig.h
index 0e1a9a9515..e9e9e19d0f 100644
--- a/sysdeps/generic/ldconfig.h
+++ b/sysdeps/generic/ldconfig.h
@@ -90,8 +90,6 @@ extern int process_file (const char *real_file_name, const char *file_name,
 			 const char *lib, int *flag, unsigned int *isa_level,
 			 char **soname, int is_link, struct stat *stat_buf);
 
-extern char *implicit_soname (const char *lib, int flag);
-
 /* Declared in readelflib.c.  */
 extern int process_elf_file (const char *file_name, const char *lib,
 			     int *flag, unsigned int *isa_level, char **soname,