From: Jeff Layton jlayton@kernel.org
[ Upstream commit df2474a22c42ce419b67067c52d71da06c385501 ]
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 Signed-off-by: Sasha Levin sashal@kernel.org --- Documentation/filesystems/mandatory-locking.txt | 10 ++++++++++ fs/namespace.c | 11 ++++++++--- 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 473446ae9e9b..11def59b0d50 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -1695,13 +1695,18 @@ 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.