Commit 43adf844 authored by peterz@infradead.org's avatar peterz@infradead.org Committed by Peter Zijlstra
Browse files

futex: FLAGS_STRICT 



The current semantics for futex_wake() are a bit loose, specifically
asking for 0 futexes to be woken actually gets you 1.

Adding a !nr check to sys_futex_wake() makes that it would return 0
for unaligned futex words, because that check comes in the shared
futex_wake() function. Adding the !nr check there, would affect the
legacy sys_futex() semantics.

Hence frob a flag :-(

Suggested-by: default avatarAndré Almeida <andrealmeid@igalia.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: default avatarThomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20230921105248.048643656@noisy.programming.kicks-ass.net
parent 9f6c532f

kernel/futex/futex.h

+11 −10
Original line number Diff line number Diff line
@@ -17,25 +17,26 @@ 
 * Futex flags used to encode options to functions and preserve them across

 * restarts.

 */

#define FLAGS_SIZE_8		0x00

#define FLAGS_SIZE_16		0x01

#define FLAGS_SIZE_32		0x02

#define FLAGS_SIZE_64		0x03

#define FLAGS_SIZE_8		0x0000

#define FLAGS_SIZE_16		0x0001

#define FLAGS_SIZE_32		0x0002

#define FLAGS_SIZE_64		0x0003



#define FLAGS_SIZE_MASK		0x03

#define FLAGS_SIZE_MASK		0x0003



#ifdef CONFIG_MMU

# define FLAGS_SHARED		0x10

# define FLAGS_SHARED		0x0010

#else

/*

 * NOMMU does not have per process address space. Let the compiler optimize

 * code away.

 */

# define FLAGS_SHARED		0x00

# define FLAGS_SHARED		0x0000

#endif

#define FLAGS_CLOCKRT		0x20

#define FLAGS_HAS_TIMEOUT	0x40

#define FLAGS_NUMA		0x80

#define FLAGS_CLOCKRT		0x0020

#define FLAGS_HAS_TIMEOUT	0x0040

#define FLAGS_NUMA		0x0080

#define FLAGS_STRICT		0x0100



/* FUTEX_ to FLAGS_ */

static inline unsigned int futex_to_flags(unsigned int op)

kernel/futex/syscalls.c

+1 −1
Original line number Diff line number Diff line
@@ -333,7 +333,7 @@ SYSCALL_DEFINE4(futex_wake, 
	if (!futex_validate_input(flags, mask))

		return -EINVAL;



	return futex_wake(uaddr, flags, nr, mask);

	return futex_wake(uaddr, FLAGS_STRICT | flags, nr, mask);

}



#ifdef CONFIG_COMPAT

kernel/futex/waitwake.c

+3 −0
Original line number Diff line number Diff line
@@ -155,6 +155,9 @@ int futex_wake(u32 __user *uaddr, unsigned int flags, int nr_wake, u32 bitset) 
	if (unlikely(ret != 0))

		return ret;



	if ((flags & FLAGS_STRICT) && !nr_wake)

		return 0;



	hb = futex_hash(&key);



	/* Make sure we really have tasks to wakeup */