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Commit 1ac0b6de authored by Kirill A. Shutemov's avatar Kirill A. Shutemov Committed by Linus Torvalds
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ipc/shm: handle removed segments gracefully in shm_mmap() 

remap_file_pages(2) emulation can reach file which represents removed
IPC ID as long as a memory segment is mapped.  It breaks expectations of
IPC subsystem.

Test case (rewritten to be more human readable, originally autogenerated
by syzkaller[1]):

	#define _GNU_SOURCE
	#include <stdlib.h>
	#include <sys/ipc.h>
	#include <sys/mman.h>
	#include <sys/shm.h>

	#define PAGE_SIZE 4096

	int main()
	{
		int id;
		void *p;

		id = shmget(IPC_PRIVATE, 3 * PAGE_SIZE, 0);
		p = shmat(id, NULL, 0);
		shmctl(id, IPC_RMID, NULL);
		remap_file_pages(p, 3 * PAGE_SIZE, 0, 7, 0);

	        return 0;
	}

The patch changes shm_mmap() and code around shm_lock() to propagate
locking error back to caller of shm_mmap().

[1] http://github.com/google/syzkaller



Signed-off-by: default avatarKirill A. Shutemov <kirill.shutemov@linux.intel.com>
Reported-by: default avatarDmitry Vyukov <dvyukov@google.com>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Manfred Spraul <manfred@colorfullife.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 64f00850

ipc/shm.c

+43 −10
Original line number Diff line number Diff line
@@ -156,11 +156,12 @@ static inline struct shmid_kernel *shm_lock(struct ipc_namespace *ns, int id) 
	struct kern_ipc_perm *ipcp = ipc_lock(&shm_ids(ns), id);



	/*

	 * We raced in the idr lookup or with shm_destroy().  Either way, the

	 * ID is busted.

	 * Callers of shm_lock() must validate the status of the returned ipc

	 * object pointer (as returned by ipc_lock()), and error out as

	 * appropriate.

	 */

	WARN_ON(IS_ERR(ipcp));



	if (IS_ERR(ipcp))

		return (void *)ipcp;

	return container_of(ipcp, struct shmid_kernel, shm_perm);

}
@@ -186,18 +187,33 @@ static inline void shm_rmid(struct ipc_namespace *ns, struct shmid_kernel *s) 
}





/* This is called by fork, once for every shm attach. */

static void shm_open(struct vm_area_struct *vma)

static int __shm_open(struct vm_area_struct *vma)

{

	struct file *file = vma->vm_file;

	struct shm_file_data *sfd = shm_file_data(file);

	struct shmid_kernel *shp;



	shp = shm_lock(sfd->ns, sfd->id);



	if (IS_ERR(shp))

		return PTR_ERR(shp);



	shp->shm_atim = get_seconds();

	shp->shm_lprid = task_tgid_vnr(current);

	shp->shm_nattch++;

	shm_unlock(shp);

	return 0;

}



/* This is called by fork, once for every shm attach. */

static void shm_open(struct vm_area_struct *vma)

{

	int err = __shm_open(vma);

	/*

	 * We raced in the idr lookup or with shm_destroy().

	 * Either way, the ID is busted.

	 */

	WARN_ON_ONCE(err);

}



/*
@@ -260,6 +276,14 @@ static void shm_close(struct vm_area_struct *vma) 
	down_write(&shm_ids(ns).rwsem);

	/* remove from the list of attaches of the shm segment */

	shp = shm_lock(ns, sfd->id);



	/*

	 * We raced in the idr lookup or with shm_destroy().

	 * Either way, the ID is busted.

	 */

	if (WARN_ON_ONCE(IS_ERR(shp)))

		goto done; /* no-op */



	shp->shm_lprid = task_tgid_vnr(current);

	shp->shm_dtim = get_seconds();

	shp->shm_nattch--;
@@ -267,6 +291,7 @@ static void shm_close(struct vm_area_struct *vma) 
		shm_destroy(ns, shp);

	else

		shm_unlock(shp);

done:

	up_write(&shm_ids(ns).rwsem);

}
@@ -388,17 +413,25 @@ static int shm_mmap(struct file *file, struct vm_area_struct *vma) 
	struct shm_file_data *sfd = shm_file_data(file);

	int ret;



	/*

	 * In case of remap_file_pages() emulation, the file can represent

	 * removed IPC ID: propogate shm_lock() error to caller.

	 */

	ret =__shm_open(vma);

	if (ret)

		return ret;



	ret = sfd->file->f_op->mmap(sfd->file, vma);

	if (ret != 0)

	if (ret) {

		shm_close(vma);

		return ret;

	}

	sfd->vm_ops = vma->vm_ops;

#ifdef CONFIG_MMU

	WARN_ON(!sfd->vm_ops->fault);

#endif

	vma->vm_ops = &shm_vm_ops;

	shm_open(vma);



	return ret;

	return 0;

}



static int shm_release(struct inode *ino, struct file *file)