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authorJeff Layton <jlayton@kernel.org>2019-08-15 15:21:17 -0400
committerJeff Layton <jlayton@kernel.org>2019-08-16 12:13:48 -0400
commitdf2474a22c42ce419b67067c52d71da06c385501 (patch)
tree5de33b456cf345e487089d640689b5aa468224d7
parent43e4cb942e88e756b41ea4d30249a47973880508 (diff)
downloadlinux-df2474a22c42ce419b67067c52d71da06c385501.tar.bz2
locks: print a warning when mount fails due to lack of "mand" support
Since 9e8925b67a ("locks: Allow disabling mandatory locking at compile time"), attempts to mount filesystems with "-o mand" will fail. Unfortunately, there is no other indiciation of the reason for the failure. Change how the function is defined for better readability. When CONFIG_MANDATORY_FILE_LOCKING is disabled, printk a warning when someone attempts to mount with -o mand. Also, add a blurb to the mandatory-locking.txt file to explain about the "mand" option, and the behavior one should expect when it is disabled. Reported-by: Jan Kara <jack@suse.cz> Reviewed-by: Jan Kara <jack@suse.cz> Signed-off-by: Jeff Layton <jlayton@kernel.org>
-rw-r--r--Documentation/filesystems/mandatory-locking.txt10
-rw-r--r--fs/namespace.c11
2 files changed, 18 insertions, 3 deletions
diff --git a/Documentation/filesystems/mandatory-locking.txt b/Documentation/filesystems/mandatory-locking.txt
index 0979d1d2ca8b..a251ca33164a 100644
--- a/Documentation/filesystems/mandatory-locking.txt
+++ b/Documentation/filesystems/mandatory-locking.txt
@@ -169,3 +169,13 @@ havoc if they lock crucial files. The way around it is to change the file
permissions (remove the setgid bit) before trying to read or write to it.
Of course, that might be a bit tricky if the system is hung :-(
+7. The "mand" mount option
+--------------------------
+Mandatory locking is disabled on all filesystems by default, and must be
+administratively enabled by mounting with "-o mand". That mount option
+is only allowed if the mounting task has the CAP_SYS_ADMIN capability.
+
+Since kernel v4.5, it is possible to disable mandatory locking
+altogether by setting CONFIG_MANDATORY_FILE_LOCKING to "n". A kernel
+with this disabled will reject attempts to mount filesystems with the
+"mand" mount option with the error status EPERM.
diff --git a/fs/namespace.c b/fs/namespace.c
index 6464ea4acba9..602bd78ba572 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -1643,13 +1643,18 @@ static inline bool may_mount(void)
return ns_capable(current->nsproxy->mnt_ns->user_ns, CAP_SYS_ADMIN);
}
+#ifdef CONFIG_MANDATORY_FILE_LOCKING
static inline bool may_mandlock(void)
{
-#ifndef CONFIG_MANDATORY_FILE_LOCKING
- return false;
-#endif
return capable(CAP_SYS_ADMIN);
}
+#else
+static inline bool may_mandlock(void)
+{
+ pr_warn("VFS: \"mand\" mount option not supported");
+ return false;
+}
+#endif
/*
* Now umount can handle mount points as well as block devices.