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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: Jeff Layton <jlayton@poochiereds.net>
Signed-off-by: Steve French <smfrench@gmail.com>
This commit is contained in:
Jeff Layton 2014-04-30 09:31:47 -04:00 committed by Steve French
parent e284e53fde
commit 4f73c7d342
4 changed files with 49 additions and 15 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
fs/cifs/cifsfs.h
View File

@ -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 *);

1
fs/cifs/cifsglob.h
View File

@ -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 */

12
fs/cifs/file.c
View File

@ -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);
}

50
fs/cifs/inode.c
View File

@ -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)