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Commit 4f73c7d3 authored by Jeff Layton's avatar Jeff Layton Committed by Steve French
Browse files

cifs: fix potential races in cifs_revalidate_mapping 



The handling of the CIFS_INO_INVALID_MAPPING flag is racy. It's possible
for two tasks to attempt to revalidate the mapping at the same time. The
first sees that CIFS_INO_INVALID_MAPPING is set. It clears the flag and
then calls invalidate_inode_pages2 to start shooting down the pagecache.

While that's going on, another task checks the flag and sees that it's
clear. It then ends up trusting the pagecache to satisfy a read when it
shouldn't.

Fix this by adding a bitlock to ensure that the clearing of the flag is
atomic with respect to the actual cache invalidation. Also, move the
other existing users of cifs_invalidate_mapping to use a new
cifs_zap_mapping() function that just sets the INVALID_MAPPING bit and
then uses the standard codepath to handle the invalidation.

Signed-off-by: default avatarJeff Layton <jlayton@poochiereds.net>
Signed-off-by: default avatarSteve French <smfrench@gmail.com>
parent e284e53f

fs/cifs/cifsfs.h

+1 −0
Original line number Diff line number Diff line
@@ -76,6 +76,7 @@ extern int cifs_revalidate_file(struct file *filp); 
extern int cifs_revalidate_dentry(struct dentry *);

extern int cifs_invalidate_mapping(struct inode *inode);

extern int cifs_revalidate_mapping(struct inode *inode);

extern int cifs_zap_mapping(struct inode *inode);

extern int cifs_getattr(struct vfsmount *, struct dentry *, struct kstat *);

extern int cifs_setattr(struct dentry *, struct iattr *);

fs/cifs/cifsglob.h

+1 −0
Original line number Diff line number Diff line
@@ -1118,6 +1118,7 @@ struct cifsInodeInfo { 
#define CIFS_INODE_DOWNGRADE_OPLOCK_TO_L2 (2) /* Downgrade oplock to L2 */

#define CIFS_INO_DELETE_PENDING		  (3) /* delete pending on server */

#define CIFS_INO_INVALID_MAPPING	  (4) /* pagecache is invalid */

#define CIFS_INO_LOCK			  (5) /* lock bit for synchronization */

	unsigned long flags;

	spinlock_t writers_lock;

	unsigned int writers;		/* Number of writers on this inode */

fs/cifs/file.c

+6 −6
Original line number Diff line number Diff line
@@ -335,7 +335,7 @@ cifs_new_fileinfo(struct cifs_fid *fid, struct file *file, 
	spin_unlock(&cifs_file_list_lock);



	if (fid->purge_cache)

		cifs_invalidate_mapping(inode);

		cifs_zap_mapping(inode);



	file->private_data = cfile;

	return cfile;
@@ -1529,7 +1529,7 @@ cifs_setlk(struct file *file, struct file_lock *flock, __u32 type, 
		 */

		if (!CIFS_CACHE_WRITE(CIFS_I(inode)) &&

					CIFS_CACHE_READ(CIFS_I(inode))) {

			cifs_invalidate_mapping(inode);

			cifs_zap_mapping(inode);

			cifs_dbg(FYI, "Set no oplock for inode=%p due to mand locks\n",

				 inode);

			CIFS_I(inode)->oplock = 0;
@@ -2218,7 +2218,7 @@ int cifs_strict_fsync(struct file *file, loff_t start, loff_t end, 
		 file->f_path.dentry->d_name.name, datasync);



	if (!CIFS_CACHE_READ(CIFS_I(inode))) {

		rc = cifs_invalidate_mapping(inode);

		rc = cifs_zap_mapping(inode);

		if (rc) {

			cifs_dbg(FYI, "rc: %d during invalidate phase\n", rc);

			rc = 0; /* don't care about it in fsync */
@@ -2649,7 +2649,7 @@ cifs_strict_writev(struct kiocb *iocb, const struct iovec *iov, 
		 * request comes - break it on the client to prevent reading

		 * an old data.

		 */

		cifs_invalidate_mapping(inode);

		cifs_zap_mapping(inode);

		cifs_dbg(FYI, "Set no oplock for inode=%p after a write operation\n",

			 inode);

		cinode->oplock = 0;
@@ -3112,7 +3112,7 @@ int cifs_file_strict_mmap(struct file *file, struct vm_area_struct *vma) 
	xid = get_xid();



	if (!CIFS_CACHE_READ(CIFS_I(inode))) {

		rc = cifs_invalidate_mapping(inode);

		rc = cifs_zap_mapping(inode);

		if (rc)

			return rc;

	}
@@ -3670,7 +3670,7 @@ void cifs_oplock_break(struct work_struct *work) 
		if (!CIFS_CACHE_READ(cinode)) {

			rc = filemap_fdatawait(inode->i_mapping);

			mapping_set_error(inode->i_mapping, rc);

			cifs_invalidate_mapping(inode);

			cifs_zap_mapping(inode);

		}

		cifs_dbg(FYI, "Oplock flush inode %p rc %d\n", inode, rc);

	}

fs/cifs/inode.c

+41 −9
Original line number Diff line number Diff line
@@ -22,6 +22,7 @@ 
#include <linux/stat.h>

#include <linux/slab.h>

#include <linux/pagemap.h>

#include <linux/freezer.h>

#include <asm/div64.h>

#include "cifsfs.h"

#include "cifspdu.h"
@@ -1762,29 +1763,60 @@ int 
cifs_invalidate_mapping(struct inode *inode)

{

	int rc = 0;

	struct cifsInodeInfo *cifs_i = CIFS_I(inode);



	clear_bit(CIFS_INO_INVALID_MAPPING, &cifs_i->flags);



	if (inode->i_mapping && inode->i_mapping->nrpages != 0) {

		rc = invalidate_inode_pages2(inode->i_mapping);

		if (rc) {

		if (rc)

			cifs_dbg(VFS, "%s: could not invalidate inode %p\n",

				 __func__, inode);

			set_bit(CIFS_INO_INVALID_MAPPING, &cifs_i->flags);

		}

	}



	cifs_fscache_reset_inode_cookie(inode);

	return rc;

}



/**

 * cifs_wait_bit_killable - helper for functions that are sleeping on bit locks

 * @word: long word containing the bit lock

 */

static int

cifs_wait_bit_killable(void *word)

{

	if (fatal_signal_pending(current))

		return -ERESTARTSYS;

	freezable_schedule_unsafe();

	return 0;

}



int

cifs_revalidate_mapping(struct inode *inode)

{

	if (test_bit(CIFS_INO_INVALID_MAPPING, &CIFS_I(inode)->flags))

		return cifs_invalidate_mapping(inode);

	return 0;

	int rc;

	unsigned long *flags = &CIFS_I(inode)->flags;



	rc = wait_on_bit_lock(flags, CIFS_INO_LOCK, cifs_wait_bit_killable,

				TASK_KILLABLE);

	if (rc)

		return rc;



	if (test_and_clear_bit(CIFS_INO_INVALID_MAPPING, flags)) {

		rc = cifs_invalidate_mapping(inode);

		if (rc)

			set_bit(CIFS_INO_INVALID_MAPPING, flags);

	}



	clear_bit_unlock(CIFS_INO_LOCK, flags);

	smp_mb__after_clear_bit();

	wake_up_bit(flags, CIFS_INO_LOCK);



	return rc;

}



int

cifs_zap_mapping(struct inode *inode)

{

	set_bit(CIFS_INO_INVALID_MAPPING, &CIFS_I(inode)->flags);

	return cifs_revalidate_mapping(inode);

}



int cifs_revalidate_file_attr(struct file *filp)