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From:   Petr Vorel <petr.vorel@gmail.com>
To:     linux-nfs@vger.kernel.org
Cc:     Joey Hess <joeyh@debian.org>, Steve Dickson <steved@redhat.com>,
        Chuck Lever <chuck.lever@oracle.com>,
        Petr Vorel <petr.vorel@gmail.com>
Subject: [nfs-utils PATCH 1/1] mount: Do not overwrite /etc/mtab if it's symlink
Date:   Wed, 20 Nov 2019 19:35:29 +0100
Message-Id: <20191120183529.29366-1-petr.vorel@gmail.com>
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Sender: linux-nfs-owner@vger.kernel.org
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From: Joey Hess <joeyh@debian.org>

Some systems have /etc/mtab symlink to /proc/mounts. In that case
mount.nfs complains:
Can't set permissions on mtab: Operation not permitted

See https://bugs.debian.org/476577

This change makes mount.nfs handle symlinked /etc/mtab the way
umount.nfs and util- linux handle it.

Cc: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Joey Hess <joeyh@debian.org>
[ pvorel: took patch from Debian, rebased for 2.4.3-rc1 and created commit
message. Patch is also used in Gentoo. ]
Signed-off-by: Petr Vorel <petr.vorel@gmail.com>
---
Hi,

if you merge, please keep Joey as the author in git :).

Kind regards,
Petr

 utils/mount/fstab.c | 2 +-
 utils/mount/fstab.h | 1 +
 utils/mount/mount.c | 7 +++++++
 3 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/utils/mount/fstab.c b/utils/mount/fstab.c
index 8b0aaf1a..146d8f40 100644
--- a/utils/mount/fstab.c
+++ b/utils/mount/fstab.c
@@ -61,7 +61,7 @@ mtab_does_not_exist(void) {
 	return var_mtab_does_not_exist;
 }
 
-static int
+int
 mtab_is_a_symlink(void) {
         get_mtab_info();
         return var_mtab_is_a_symlink;
diff --git a/utils/mount/fstab.h b/utils/mount/fstab.h
index 313bf9b3..8676c8c2 100644
--- a/utils/mount/fstab.h
+++ b/utils/mount/fstab.h
@@ -7,6 +7,7 @@
 #define _PATH_FSTAB "/etc/fstab"
 #endif
 
+int mtab_is_a_symlink(void);
 int mtab_is_writable(void);
 int mtab_does_not_exist(void);
 void reset_mtab_info(void);
diff --git a/utils/mount/mount.c b/utils/mount/mount.c
index 91f10877..92a0dfe4 100644
--- a/utils/mount/mount.c
+++ b/utils/mount/mount.c
@@ -204,6 +204,13 @@ create_mtab (void) {
 	int flags;
 	mntFILE *mfp;
 
+	/* Avoid writing if the mtab is a symlink to /proc/mounts, since
+	   that would create a file /proc/mounts in case the proc filesystem
+	   is not mounted, and the fchmod below would also fail. */
+	if (mtab_is_a_symlink()) {
+		return EX_SUCCESS;
+	}
+
 	lock_mtab();
 
 	mfp = nfs_setmntent (MOUNTED, "a+");
-- 
2.24.0