[glibc] linux: use __fd_to_filename helper function instead of snprintf.

[Adhemerval Zanella <azanella@sourceware.org>]

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=77c1573dbceebf75203e4201615def9765599d87

commit 77c1573dbceebf75203e4201615def9765599d87
Author: Érico Nogueira <ericonr@disroot.org>
Date:   Tue Apr 27 10:09:45 2021 -0300

    linux: use __fd_to_filename helper function instead of snprintf.
    
    Change made to fchmodat and fexecve. There are tests using xasprintf
    instead of this helper as well, but this commit doesn't touch them.

Diff:
---
 sysdeps/unix/sysv/linux/fchmodat.c | 13 +++----------
 sysdeps/unix/sysv/linux/fexecve.c  | 10 ++++------
 2 files changed, 7 insertions(+), 16 deletions(-)

diff --git a/sysdeps/unix/sysv/linux/fchmodat.c b/sysdeps/unix/sysv/linux/fchmodat.c
index f264f0c09d..5bd1eb96a5 100644
--- a/sysdeps/unix/sysv/linux/fchmodat.c
+++ b/sysdeps/unix/sysv/linux/fchmodat.c
@@ -18,6 +18,7 @@
 
 #include <errno.h>
 #include <fcntl.h>
+#include <fd_to_filename.h>
 #include <not-cancel.h>
 #include <stdio.h>
 #include <sys/stat.h>
@@ -69,16 +70,8 @@ fchmodat (int fd, const char *file, mode_t mode, int flag)
 
       /* For most file systems, fchmod does not operate on O_PATH
 	 descriptors, so go through /proc.  */
-      char buf[32];
-      if (__snprintf (buf, sizeof (buf), "/proc/self/fd/%d", pathfd) < 0)
-	{
-	  /* This also may report strange error codes to the caller
-	     (although snprintf really should not fail).  */
-	  __close_nocancel (pathfd);
-	  return -1;
-	}
-
-      int ret = __chmod (buf, mode);
+      struct fd_to_filename filename;
+      int ret = __chmod (__fd_to_filename (pathfd, &filename), mode);
       if (ret != 0)
 	{
 	  if (errno == ENOENT)
diff --git a/sysdeps/unix/sysv/linux/fexecve.c b/sysdeps/unix/sysv/linux/fexecve.c
index f37c245396..df25c2acb8 100644
--- a/sysdeps/unix/sysv/linux/fexecve.c
+++ b/sysdeps/unix/sysv/linux/fexecve.c
@@ -22,6 +22,7 @@
 #include <fcntl.h>
 #include <sys/stat.h>
 
+#include <fd_to_filename.h>
 #include <sysdep.h>
 #include <sys/syscall.h>
 #include <kernel-features.h>
@@ -49,12 +50,9 @@ fexecve (int fd, char *const argv[], char *const envp[])
 
 #ifndef __ASSUME_EXECVEAT
   /* We use the /proc filesystem to get the information.  If it is not
-     mounted we fail.  */
-  char buf[sizeof "/proc/self/fd/" + sizeof (int) * 3];
-  __snprintf (buf, sizeof (buf), "/proc/self/fd/%d", fd);
-
-  /* We do not need the return value.  */
-  __execve (buf, argv, envp);
+     mounted we fail.  We do not need the return value.  */
+  struct fd_to_filename filename;
+  __execve (__fd_to_filename (fd, &filename), argv, envp);
 
   int save = errno;