The commit 90f7d7a0d0d6 ("locks: remove LOCK_MAND flock lock support")
removed LOCK_MAND support from the kernel because nothing checked the
flag, nor was there no use case. This patch revives LOCK_MAND to
introduce a mandatory lock for read/write on /proc/sys. Currently, it's
the only use case, so we added two changes while reverting the commit.
First, we used to allow any f_mode for LOCK_MAND, but now we don't get
it back. Instead, we enforce being FMODE_READ|FMODE_WRITE as LOCK_SH
and LOCK_EX.
Second, when f_ops->flock() was called with LOCK_MAND, each function
returned -EOPNOTSUPP. The following patch does not use f_ops->flock(),
so we put the validation before calling f_ops->flock().
Signed-off-by: Kuniyuki Iwashima <kuniyu@xxxxxxxxxx>
---
fs/locks.c | 57 ++++++++++++++++++++------------
include/uapi/asm-generic/fcntl.h | 5 ---
2 files changed, 35 insertions(+), 27 deletions(-)
diff --git a/fs/locks.c b/fs/locks.c
index c266cfdc3291..03ff10a3165e 100644
--- a/fs/locks.c
+++ b/fs/locks.c
@@ -421,6 +421,10 @@ static inline int flock_translate_cmd(int cmd) {
case LOCK_UN:
return F_UNLCK;
}
+
+ if (cmd & LOCK_MAND)
+ return cmd & (LOCK_MAND | LOCK_RW);
+
return -EINVAL;
}
@@ -879,6 +883,10 @@ static bool flock_locks_conflict(struct file_lock *caller_fl,
if (caller_fl->fl_file == sys_fl->fl_file)
return false;
+ if (caller_fl->fl_type & LOCK_MAND ||
+ sys_fl->fl_type & LOCK_MAND)
+ return true;
+
return locks_conflict(caller_fl, sys_fl);
}
@@ -2077,9 +2085,7 @@ EXPORT_SYMBOL(locks_lock_inode_wait);
* - %LOCK_SH -- a shared lock.
* - %LOCK_EX -- an exclusive lock.
* - %LOCK_UN -- remove an existing lock.
- * - %LOCK_MAND -- a 'mandatory' flock. (DEPRECATED)
- *
- * %LOCK_MAND support has been removed from the kernel.
+ * - %LOCK_MAND -- a 'mandatory' flock. (only supported on /proc/sys/)
*/
SYSCALL_DEFINE2(flock, unsigned int, fd, unsigned int, cmd)
{
@@ -2087,19 +2093,6 @@ SYSCALL_DEFINE2(flock, unsigned int, fd, unsigned int, cmd)
struct file_lock fl;
struct fd f;
- /*
- * LOCK_MAND locks were broken for a long time in that they never
- * conflicted with one another and didn't prevent any sort of open,
- * read or write activity.
- *
- * Just ignore these requests now, to preserve legacy behavior, but
- * throw a warning to let people know that they don't actually work.
- */
- if (cmd & LOCK_MAND) {
- pr_warn_once("Attempt to set a LOCK_MAND lock via flock(2). This support has been removed and the request ignored.\n");
- return 0;
- }
-
type = flock_translate_cmd(cmd & ~LOCK_NB);
if (type < 0)
return type;
@@ -2109,6 +2102,7 @@ SYSCALL_DEFINE2(flock, unsigned int, fd, unsigned int, cmd)
if (!f.file)
return error;
+ /* LOCK_MAND supports only read/write on proc_sysctl for now */
if (type != F_UNLCK && !(f.file->f_mode & (FMODE_READ | FMODE_WRITE)))
goto out_putf;
@@ -2122,12 +2116,18 @@ SYSCALL_DEFINE2(flock, unsigned int, fd, unsigned int, cmd)
if (can_sleep)
fl.fl_flags |= FL_SLEEP;
- if (f.file->f_op->flock)
+ if (f.file->f_op->flock) {
+ if (cmd & LOCK_MAND) {
+ error = -EOPNOTSUPP;
+ goto out_putf;
+ }
+
error = f.file->f_op->flock(f.file,
(can_sleep) ? F_SETLKW : F_SETLK,
&fl);
- else
+ } else {
error = locks_lock_file_wait(f.file, &fl);
+ }
out_putf:
fdput(f);
@@ -2711,7 +2711,11 @@ static void lock_get_status(struct seq_file *f, struct file_lock *fl,
seq_printf(f, " %s ",
(inode == NULL) ? "*NOINODE*" : "ADVISORY ");
} else if (IS_FLOCK(fl)) {
- seq_puts(f, "FLOCK ADVISORY ");
+ if (fl->fl_type & LOCK_MAND) {
+ seq_puts(f, "FLOCK MANDATORY ");
+ } else {
+ seq_puts(f, "FLOCK ADVISORY ");
+ }
} else if (IS_LEASE(fl)) {
if (fl->fl_flags & FL_DELEG)
seq_puts(f, "DELEG ");
@@ -2727,10 +2731,19 @@ static void lock_get_status(struct seq_file *f, struct file_lock *fl,
} else {
seq_puts(f, "UNKNOWN UNKNOWN ");
}
- type = IS_LEASE(fl) ? target_leasetype(fl) : fl->fl_type;
- seq_printf(f, "%s ", (type == F_WRLCK) ? "WRITE" :
- (type == F_RDLCK) ? "READ" : "UNLCK");
+ if (fl->fl_type & LOCK_MAND) {
+ seq_printf(f, "%s ",
+ (fl->fl_type & LOCK_READ)
+ ? (fl->fl_type & LOCK_WRITE) ? "RW " : "READ "
+ : (fl->fl_type & LOCK_WRITE) ? "WRITE" : "NONE ");
+ } else {
+ type = IS_LEASE(fl) ? target_leasetype(fl) : fl->fl_type;
+
+ seq_printf(f, "%s ", (type == F_WRLCK) ? "WRITE" :
+ (type == F_RDLCK) ? "READ" : "UNLCK");
+ }
+
if (inode) {
/* userspace relies on this representation of dev_t */
seq_printf(f, "%d %02x:%02x:%lu ", fl_pid,
diff --git a/include/uapi/asm-generic/fcntl.h b/include/uapi/asm-generic/fcntl.h
index 1ecdb911add8..94fb8c6fd543 100644
--- a/include/uapi/asm-generic/fcntl.h
+++ b/include/uapi/asm-generic/fcntl.h
@@ -180,11 +180,6 @@ struct f_owner_ex {
#define LOCK_NB 4 /* or'd with one of the above to prevent
blocking */
#define LOCK_UN 8 /* remove lock */
-
-/*
- * LOCK_MAND support has been removed from the kernel. We leave the symbols
- * here to not break legacy builds, but these should not be used in new code.
- */
#define LOCK_MAND 32 /* This is a mandatory flock ... */
#define LOCK_READ 64 /* which allows concurrent read operations */
#define LOCK_WRITE 128 /* which allows concurrent write operations */
--
2.30.2
