[glibc] hurd: Fix readlink() hanging on fifo

[Samuel Thibault <sthibaul@sourceware.org>]

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=9e5c991106cb04b489272de0ef6a7a6bcef50477

commit 9e5c991106cb04b489272de0ef6a7a6bcef50477
Author: Samuel Thibault <samuel.thibault@ens-lyon.org>
Date:   Wed Sep 14 18:52:52 2022 +0200

    hurd: Fix readlink() hanging on fifo
    
    readlink() opens the target with O_READ to be able to read the symlink
    content. When the target is actually a fifo, that would hang waiting for a
    writer (caught in the coreutils testsuite). We thus have to first lookup the
    target without O_READ to perform io_stat and lookout for fifos, and only
    after checking the symlink type, we can re-lookup with O_READ.

Diff:
---
 sysdeps/mach/hurd/readlink.c   | 5 ++++-
 sysdeps/mach/hurd/readlinkat.c | 5 ++++-
 2 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/sysdeps/mach/hurd/readlink.c b/sysdeps/mach/hurd/readlink.c
index 770462714f..2d75ef7725 100644
--- a/sysdeps/mach/hurd/readlink.c
+++ b/sysdeps/mach/hurd/readlink.c
@@ -31,7 +31,7 @@ __readlink (const char *file_name, char *buf, size_t len)
   file_t file;
   struct stat64 st;
 
-  file = __file_name_lookup (file_name, O_READ | O_NOLINK, 0);
+  file = __file_name_lookup (file_name, O_NOLINK, 0);
   if (file == MACH_PORT_NULL)
     return -1;
 
@@ -41,6 +41,9 @@ __readlink (const char *file_name, char *buf, size_t len)
       {
 	char *rbuf = buf;
 
+	__mach_port_deallocate (__mach_task_self (), file);
+	file = __file_name_lookup (file_name, O_READ | O_NOLINK, 0);
+
 	err = __io_read (file, &rbuf, &len, 0, len);
 	if (!err && rbuf != buf)
 	  {
diff --git a/sysdeps/mach/hurd/readlinkat.c b/sysdeps/mach/hurd/readlinkat.c
index 059aad9f58..113b92b732 100644
--- a/sysdeps/mach/hurd/readlinkat.c
+++ b/sysdeps/mach/hurd/readlinkat.c
@@ -32,7 +32,7 @@ readlinkat (int fd, const char *file_name, char *buf, size_t len)
   file_t file;
   struct stat64 st;
 
-  file = __file_name_lookup_at (fd, 0, file_name, O_READ | O_NOLINK, 0);
+  file = __file_name_lookup_at (fd, 0, file_name, O_NOLINK, 0);
   if (file == MACH_PORT_NULL)
     return -1;
 
@@ -42,6 +42,9 @@ readlinkat (int fd, const char *file_name, char *buf, size_t len)
       {
 	char *rbuf = buf;
 
+	__mach_port_deallocate (__mach_task_self (), file);
+	file = __file_name_lookup_at (fd, 0, file_name, O_READ | O_NOLINK, 0);
+
 	err = __io_read (file, &rbuf, &len, 0, len);
 	if (!err && rbuf != buf)
 	  {